cummings+2007

REVIEW

Carbohydrate terminology and classification

JH Cummings1 and AM Stephen2

1Gut group, Division of Pathology and Neuroscience, Ninewells Hospital and Medical School, Dundee, UK and 2Population NutritionResearch, MRC Human Nutrition Research, Elsie Widdowson Laboratory, Cambridge, UK

Dietary carbohydrates are a group of chemically defined substances with a range of physical and physiological properties andhealth benefits. As with other macronutrients, the primary classification of dietary carbohydrate is based on chemistry, that ischaracter of individual monomers, degree of polymerization (DP) and type of linkage (a or b), as agreed at the Food andAgriculture Organization/World Health Organization Expert Consultation in 1997. This divides carbohydrates into three maingroups, sugars (DP 12), oligosaccharides (short-chain carbohydrates) (DP 39) and polysaccharides (DPX10). Within thisclassification, a number of terms are used such as mono- and disaccharides, polyols, oligosaccharides, starch, modified starch,non-starch polysaccharides, total carbohydrate, sugars, etc. While effects of carbohydrates are ultimately related to their primarychemistry, they are modified by their physical properties. These include water solubility, hydration, gel formation, crystallinestate, association with other molecules such as protein, lipid and divalent cations and aggregation into complex structures in cellwalls and other specialized plant tissues. A classification based on chemistry is essential for a system of measurement, predicationof properties and estimation of intakes, but does not allow a simple translation into nutritional effects since each class ofcarbohydrate has overlapping physiological properties and effects on health. This dichotomy has led to the use of a number ofterms to describe carbohydrate in foods, for example intrinsic and extrinsic sugars, prebiotic, resistant starch, dietary fibre,available and unavailable carbohydrate, complex carbohydrate, glycaemic and whole grain. This paper reviews these terms andsuggests that some are more useful than others. A clearer understanding of what is meant by any particular word used todescribe carbohydrate is essential to progress in translating the growing knowledge of the physiological properties ofcarbohydrate into public health messages.

European Journal of Clinical Nutrition (2007) 61 (Suppl 1), S5S18. doi:10.1038/sj.ejcn.1602936

Keywords: carbohydrate; sugars; oligosaccharides; starch; dietary fibre; classification

Introduction

The dietary carbohydrates are a diverse group of substances

with a range of chemical, physical and physiological proper-

ties. While carbohydrates are principally substrates for

energy metabolism, they can affect satiety, blood glucose

and insulin, lipid metabolism and, through fermentation,

exert a major control on colonic function, including bowel

habit, transit, the metabolism and balance of the commensal

flora and large bowel epithelial cell health. They may also be

immunomodulatory and influence calcium absorption.

These properties have implications for our overall health;

contributing particularly to the control of body weight,

diabetes and ageing, cardiovascular disease, bone mineral

density, large bowel cancer, constipation and resistance to

gut infection.

Classification

As for other macronutrients, the primary classification of

dietary carbohydrates, as proposed at the Joint Food and

Agriculture Organization (FAO)/World Health Organization

(WHO) Expert Consultation on Carbohydrates in human

nutrition convened in Rome in 1997 (FAO, 1998), is by

molecular size, as determined by degree of polymerization

(DP), the type of linkage (a or non-a) and character ofindividual monomers (Table 1). This classification is analo-

gous to that used for dietary fat, which is based on carbon

chain length, number and position of double bonds and

their configuration as cis or trans. A chemical approach is

necessary for a coherent and enforceable approach to

measurement and labelling forms the basis for terminology

Correspondence: Professor JH Cummings, Division of Pathology and

Neuroscience, Ninewells Hospital and Medical School, Dundee DD1 9SY, UK.

E-mail: [email protected]

European Journal of Clinical Nutrition (2007) 61 (Suppl 1), S5S18& 2007 Nature Publishing Group All rights reserved 0954-3007/07 $30.00

www.nature.com/ejcn

title

and an understanding of the physiological and health effects

of these macronutrients.

A chemical approach divides carbohydrates into three

main groups, sugars (DP12), oligosaccharides (short-chain

carbohydrates) (DP39) and polysaccharides (DPX10).Sugars comprise (i) monosaccharides, (ii) disaccharides and

(iii) polyols (sugar alcohols). Oligosaccharides are either (a)

malto-oligosaccharides (a-glucans), principally occurringfrom the hydrolysis of starch and (b) non-a-glucan such asraffinose and stachyose (a galactosides), fructo- and galacto-oligosaccharides and other oligosaccharides. Polysaccharides

may be divided into starch (a-1:4 and 1:6 glucans) and non-starch polysaccharides (NSPs), of which the major compo-

nents are the polysaccharides of the plant cell wall such as

cellulose, hemicellulose and pectin but also includes plant

gums, mucilages and hydrocolloids. Some carbohydrates,

like inulin, do not fit neatly into this scheme because they

exist in nature in multiple molecular forms. Inulin, GFN,

from plants may have from 2 to 200 fructose units and so

crosses the boundary between oligosaccharides and poly-

saccharides (Roberfroid, 2005).

A variety of methodologies are available for the measure-

ment of the carbohydrate content of food and the compo-

nents are listed in Table 1 (Englyst et al., 2007).

Terminology

Total carbohydrate

Although the individual components of dietary carbohy-

drate are readily identifiable, there is some confusion as to

what comprises total carbohydrate as reported in food tables.

Two principal approaches to total carbohydrate are used,

first, that derived by difference and second, the direct

measurement of the individual components that are then

combined to give a total. Calculating carbohydrate by

difference has been used since the early 20th century and

is still widely used around the world (Atwater and Woods,

1986; United States Department of Agriculture, 2007). The

moisture, protein, fat, ash and alcohol content of a food are

determined, subtracted from the total weight of the food and

the remainder, or difference, is considered to be carbohy-

drate. There are, however, a number of problems with this

approach in that the by difference figure includes non-

carbohydrate components such as lignin, organic acids,

tannins, waxes and some Maillard products. In addition to

this error, it combines all the analytical errors from the other

analyses. Also, a single global figure for carbohydrates in

food is uninformative because it fails to identify the many

types of carbohydrates and thus to allow some under-

standing of the potential health benefits of those foods.

Direct analysis of carbohydrate components and summa-

tion to obtain a total carbohydrate value has been the basis

of carbohydrate analysis in the UK since 1929, when the first

values were published by McCance and Lawrence (1929).

Those countries that use McCance and Widdowsons, The

Composition of Foods (Food Standards Agency/Institute

of Food Research, 2002) also express carbohydrate using

this approach. The total figure obtained is for what McCance

and Lawrence called available carbohydrate and therefore

differs from carbohydrate by difference in that it does not

contain the plant cell wall polysaccharides (fibre). In

addition, it is not complicated by analytical difficulties with

other food components. Dietary intake of total carbohydrate

and its components using direct analysis enables examina-

tion of geographic variations and changes in intake over

time of individual carbohydrate types and their relationship

with health outcomes. Total carbohydrate by direct measure-

ment is preferable and simplified methods to do this should

be developed.

Figures obtained for carbohydrate by difference and

carbohydrate analysed directly are not always the same,

particularly for complex mixtures, and foods containing fibre

or certain types of starch, like pasta (Stephen, 2006). This

results in apparently different carbohydrate intakes for the

same list of foods consumed, as shown in Table 2. Fifty-two

dietary records from a study conducted in Canada, where

carbohydrate by difference is used (Health Canada, 2005)

were subsequently analysed in the UK using values based on

McCance and Widdowsons The Composition of Foods (Hol-

land et al., 1991b, 1992). In this study, energy intake was 12%

higher and carbohydrate intake 14% higher when measured

by difference (Stephen, 2006). Comparison of carbohydrate

intake among different countries should therefore be viewed

with caution if the method of carbohydrate determination is

not the same. Worldwide variations in carbohydrate intake

assumed to be due to differences in types of foods consumed,

are also, in part, due to methodology.

Table 1 The major dietary carbohydrates

Class (DPa) Subgroup Principal components

Sugars (12) Monosaccharides Glucose, fructose, galactoseDisaccharides Sucrose, lactose, maltose,

trehalosePolyols (sugaralcohols)

Sorbitol, mannitol, lactitol,xylitol, erythritol, isomalt,maltitol

Oligosaccharides(39) (short-chaincarbohydrates)

Malto-oligosaccharides(a-glucans)

Maltodextrins

Non-a-glucanoligosaccharides

Raffinose, stachyose, fructo andgalacto oligosaccharides,polydextrose, inulin

Polysaccharides(X10)

Starch(a-glucans)

Amylose, amylopectin, modifiedstarches

Non-starchpolysaccharides(NSPs)

Cellulose, hemicellulose, pectin,arabinoxylans, b-glucan,glucomannans, plant gums andmucilages, hydrocolloids

aDegree of polymerization or number of monomeric (single sugar) units.

Based on Food and Agriculture Organization/World Health Organization

Carbohydrates in Human Nutrition report (1998), and Cummings et al.

(1997).

Carbohydrate terminology and classificationJH Cummings and AM Stephen

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European Journal of Clinical Nutrition

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Sugars

The term sugars is conventionally used to describe the

mono- and disaccharides in food.

The three principal monosaccharides are glucose, fructose

and galactose, which are the building blocks of naturally

occurring di-, oligo- and polysaccharides. Free glucose and

fructose occur in honey and cooked or dried fruit (invert

sugar), in small amounts, and in larger amounts in fruit and

berries where they are the main energy source (Holland et al.,

1992). Corn syrup, a glucose syrup produced by the

hydrolysis of cornstarch, and high fructose corn syrup,

containing glucose and fructose, are increasingly used by the

food industry in many countries. Fructose is the sweetest of

all the food carbohydrates. Sugars are used as a sweetener to

improve the palatability of many foods and beverages, and

are also used for food preservation and in jams and jellies.

Sugars confer functional characteristics to foods, like visco-

sity, texture, body and browning capacity. They increase

dough yield in baked goods, influence starch and protein

breakdown, and control moisture thus preventing drying out

(Institute of Medicine, 2001).

The polyols, such as sorbitol are alcohols of glucose and

other sugars. They are found naturally in some fruits and are

made commercially by using aldose reductase to convert the

aldehyde group of the glucose molecule to the alcohol.

Sorbitol is used as a replacement for sucrose in the diet of

people with diabetes.

The principal disaccharides are sucrose (a-Glc(1-2)b-Fru)and lactose (b-Gal(1-4)Glc). Sucrose is found very widely infruits, berries and vegetables, and can be extracted from

sugar cane or beet. Lactose is the main sugar in milk. Of the

less abundant disaccharides, maltose, derived from starch,

occurs in sprouted wheat and barley. Trehalose (a-Glc(1-4)a-Glc) is found in yeast, fungi (mushrooms) and in smallamounts in bread and honey. It is used by the food industry

as a replacement for sucrose where less sweet taste is desired

but with similar technological properties.

Because of the perceived negative impact of sugars on

health, a number of terms have been used to categorize them

more specifically, mainly to highlight their origin and

identify them for labelling purposes, for example total

sugars, added sugar, free sugars (WHO, 2003), refined sugars

(Nordic Council, 2004), discretionary sugar (New Zealand

Nutrition Foundation, 2004) and intrinsic sugars, milk

sugars and non-milk extrinsic sugars (Department of Health,

1989).

Total sugars

For labelling purposes, the category of total sugars has been

proposed. This includes all sugars from whatever source in a

food, and is defined as all monosaccharides and disaccha-

rides other than polyols (European Communities, 1990).

This term is now accepted by the European Union, Australia

and New Zealand and may well be adopted by other

countries. It is probably the most useful way to describe,

measure and label sugars.

Free sugars

Traditionally free sugars referred to any sugars in a food that

were free and not bound (Holland et al., 1992), and included

all mono- and disaccharides present in a food, including

lactose (Southgate, 1978). This term was also used analyti-

cally to describe when the carbohydrate in a food was

hydrolysed and components detected by chromatography or

colorimetric methods (Southgate, 1978). In recent years, the

use of the term free sugars has changed, to refer to all

monosaccharides and disaccharides added to foods by the

manufacturer, cook and consumer, plus sugars naturally

present in honey, syrups and fruit juices and was the

preferred term for the WHO/FAO Expert Consultation on

Diet, Nutrition and the Prevention of Chronic Diseases

(WHO, 2003). This new meaning of the term reflects the

same sources as those captured in the term non-milk

extrinsic sugars outlined below. However, it is entirely

different from the traditional use of the term by the analyst,

which is a potential source of confusion.

Added sugars

In the United States, added sugars is a commonly used term

and comprises sugars and syrups that are added to foods

during processing or preparation (Institute of Medicine,

2001). In the new United States Department of Agriculture

food composition tables, added sugars are defined as those

sugars added to foods and beverages during processing or

home preparation (Pehrsson et al., 2005). This would include

sugars listed in the ingredient list on a food product,

including honey, molasses, fruit juice concentrate, brown

sugar, corn sweetener, sucrose, lactose, glucose, high-fructose

corn syrup and malt syrup.

Extrinsic and intrinsic sugars

These terms had their origin in a United Kingdom (UK)

Department of Health Committee report in 1989 (Department

Table 2 Energy and macronutrient intakes for 52 weighed recordsanalysed using Canadian and UK food tables

Energy(kcal)

Protein(g) (%)

Fat(g) (%)

CHO(g) (%)

Analysis using Canadian nutrient file

Mean of 52 records 2265 95.9 (16.9) 81.4 (31.5) 294.2 (52.9)

Analysis using The composition of foodsMean of 52 records 1992* 89.8 (17.9) 74.5 (32.7) 252.4* (48.5)*

*Po0.001.From Stephen, 2006.


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of Health, 1989), which examined the role of sugars in the

diet. The terms were developed to distinguish sugar as

naturally integrated into the cellular structure of a food

(intrinsic) from those that are free in the food or added to it

(extrinsic). These were defined in the report as:

Intrinsic sugars. Sugars forming an integral part of certain

unprocessed foodstuffs, that is enclosed in the cell, the most

important being whole fruits and vegetables (containing

mainly fructose, glucose and sucrose). Intrinsic sugars are

therefore naturally occurring and are always accompanied by

other nutrients.

Extrinsic sugars. Sugars not located within the cellular

structure of a food. Extrinsic sugars are mainly found in fruit

juice and are those added to processed foods. Lactose in milk

is extrinsic in that it is not found within the cellular

structure of food and has important nutritional benefits, so

the term non-milk extrinsic sugars was introduced to

indicate the group of sugars, other than intrinsic and milk

sugars, that should be restricted in the diet.

Non-milk extrinsic sugars. All extrinsic sugars, which are

not from milk, that is excluding lactose. This includes fruit

juices and honey and those sugars added to foods as a

sweetener in cooking or at the table, as in hot drinks and

breakfast cereal, or during processing. This terminology has

remained popular among nutritionists in the UK, and is used

in dietary surveys and other reports where intakes are

described (Gibson, 2000; Kelly et al., 2005). However, it is

not well understood by the public and is not used in public

communications about sugars.

Dividing sugars into intrinsic and extrinsic creates pro-

blems for the analyst and, therefore, for food labelling.

While ingredient lists can be used to identify the source of

sugars in foods, analytically it is not readily possible to

distinguish their origin in a processed food.

Other terms in use include sugars, sugar, discretionary

sugar, refined sugars, refined sugar, natural sugar and

total available sugars (Stephen and Thane, 2007). Some of

these appear to equate to sucrose only, and within the EU

sucrose may be designated as sugars on food labels

(European Communities, 2000). Many of the terms are used

in publications about intakes, often with little reference to

what components they include. This has the result of

making intake comparisons very difficult and points to the

need for a uniform terminology. There is little justification

for most of these terms apart from total sugars and their

subdivision into mono- and disaccharides. The relation of

sugars to health is determined more by the food matrix

in which they are contained and more thought should be

given to characterizing this because it also affects the other

nutrients in the food, and these many alternative terms do

not really describe a property of sugars per se.

Oligosaccharides, short-chain carbohydrates

Oligosaccharides are compounds in which monosaccharide

units are joined by glycosidic linkages. Their DP has been

variously defined as including anything from 2 to 19

monosaccharide units (http://www.britannica.com/eb/

article-9057022/oligosaccharide; British Nutrition Foundation,

1990; Food and Drug Administration, 1993). However, the

disaccharides (DP2) are thought of as sugars by nutritionists

(Roberfroid et al., 1993; Asp, 1995; Cummings and Englyst,

1995; Southgate, 1995), although a disaccharide composed

of two fructose residues, for example inulobiose, is consid-

ered a fructan (Roberfroid, 2005).

The dividing line between oligo- and polysaccharides is

also arbitrary since there is a continuum of molecular size

from simple sugars to complex polymers of DP 100 000 or

more in food. Most authorities recommend a DP of 10 as

the dividing point between oligo- and polysaccharides (IUB

IUPAC and Joint Commission on Biochemical Nomencla-

ture, 1982), although in the most recent International Union

of Pure and Applied ChemistryInternational Union of

Biochemistry Nomenclature Recommendation the issue is

not really addressed and a polysaccharide is just considered

to be a macromolecule consisting of a large number of

monosaccharide (glycose) residues joined to each other by

glycosidic linkages (IUPACIUB Joint Commission on

Biochemical Nomenclature, 1996).

In practice, precipitation from aqueous solutions with

80%v/v ethanol is the step used in many carbohydrate

analysis procedures to separate these two groups (Southgate,

1991; Prosky et al., 1992; Englyst et al., 1994). However, some

branched-chain carbohydrates of DP between 10 and 100

remain in solution in 80% v/v ethanol so there is no clear

and absolute division. Furthermore, carbohydrates such as

inulin and polydextrose contain mixtures of polymers of

different chain lengths that cross the oligosaccharide/poly-

saccharide boundary. In categorizing oligosaccharides found

normally in the diet, alcohol precipitation would seem to be

the most practical way of delineating them from polysac-

charides. For novel oligosaccharides, such as that are now

being developed by the food industry as ingredients, the

average DP for that particular substance, as determined by

the manufacturer, should provide the basis on which to put

it into the appropriate carbohydrate class. In the light of the

lack of clarity surrounding the definition of oligosaccharides,

the Paris carbohydrate group suggested calling this group

short-chain carbohydrates (Cummings et al., 1997).

Food oligosaccharides fall into two groups: (i) maltodex-

trins, which are mostly derived from starch and include

maltotriose and a-limit dextrins that have both a14 anda16 bonds and an average DP8. Maltodextrins are widelyused in the food industry as sweeteners, fat substitutes and to

modify the texture of food products. They are digested and

absorbed like other a-glucans and (ii) oligosaccharides thatare not a-glucans. These oligosaccharides include raffinose(a-Gal(1-6)a-Glc(1-2)b-Fru), stachyose ((Gal)2 1:6 Glu 1:2Fru) and verbascose ((Gal)3 1:6 Glu 1:2 Fru). They are in

effect, sucrose joined to varying numbers of galactose

molecules and are found in a variety of plant seeds, for

example peas, beans and lentils. Also important in this group


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are inulin and fructo oligosaccharides (a-Glc(1-2)b-Fru(2-1)b-Fru(N) or b-Fru(2-1)b-Fru(N)). They are fructans and are thestorage carbohydrates in artichokes and chicory with small

amounts of low molecular weight found in wheat, rye,

asparagus and members of the onion, leek and garlic family.

They can be produced industrially. The chemical bonds

linking these oligosaccharides are not a-1,4 or 1,6 glucansand, therefore, they are not susceptible to pancreatic or

brush border enzyme breakdown (Oku et al., 1984; Hidaka

et al., 1986; Cummings et al., 2001). They have become

known as non-digestible oligosaccharides (Roberfroid et al.,

1993). Some of them, mainly the fructans and galactans,

have unique properties in the gut and are known as

prebiotics (see later).

Milk oligosaccharides

Milk, especially human milk, contains oligosaccharides that

are predominantly galactose containing, although great

diversity of structure is found (Kunz et al., 2000). Almost

all carry lactose at their reducing end and are elongated by

addition of N-acetylglucosamine-linked b13 or b16 to agalactose residue, followed by further galactose with b13 orb14 bonds. Other monomers include L-fucose and sialicacid. The principal oligosaccharide in milk is lacto-N-

tetraose. Total oligosaccharides in human milk are in the

range 5.08.0 g/l, but only trace amounts are present in cows

milk (Ward et al., 2006).

The oligosaccharides of breast milk have long been

credited with being the principal growth factor for bifido-

bacteria in the infant gut and thus primarily responsible for

these bacteria dominating the microbiota found in breast-fed

babies. In this context, milk oligosaccharides are acting as

prebiotics. Bifidobacteria can grow on milk oligosaccharides

as their sole carbon source while lactobacilli may not be able

to do so (Ward et al., 2006). The similarities between milk

oligosaccharide structure and epithelial cell surface carbohy-

drates in the gut suggest that milk oligosaccharides may act

as soluble receptors for gut pathogens and thus form an

essential part of colonization resistance. They may also be

immunomodulatory.

Starch and modified starch

Starch, the principal carbohydrate in most diets, is the

storage carbohydrate of plants such as cereals, root vegeta-

bles and legumes and consists of only glucose molecules. It

occurs in a partially crystalline form in granules and

comprises two polymers: amylose (DPB103) and amylopec-tin (DPB104105). Most common cereal starches contain1530% amylose, which is a non-branching helical chain of

glucose residues linked by a-1,4 glucosidic bonds. Amylo-pectin is a high-molecular-weight, highly branched polymer

containing both a-1,4 and a-1,6 linkages. Some starches frommaize, rice, sorghum and barley contain largely amylopectin

and are known as waxy. The crystalline form of the amylose

and amylopectin in the starch granules confers on them

distinct X-ray diffraction patterns, A, B and C. The A type is

characteristic of cereals (rice, wheat and maize), the B type of

potato, banana and high amylose starches while the C type is

intermediate between A and B and found in legumes. In their

native (raw) form, the B starches are resistant to digestion by

pancreatic amylase. The crystalline structure is lost when

starch is heated in water (gelatinization), thus permitting

digestion to take place. Recrystallization (retrogradation)

takes place to a variable extent after cooking and is in the B

form (Galliard, 1987; Hoover and Sosulski, 1991).

Modified starch

The proportions of amylose and amylopectin in a starchy

food are variable and can be altered by plant breeding.

Different cultivars of common species such as rice, have a

wide range of amylose to amylopectin ratios (Kennedy and

Burlingame, 2003). Techniques are rapidly emerging,

enabling starches to be produced for specific purposes by

genetically modifying the crop used for their production

(Regina et al., 2006). High amylose cornstarch and high

amylopectin (waxy) cornstarch have been available for some

time, and display quite different functional as well as

nutritional properties. High amylose starches require higher

temperatures for gelatinization and are more prone to

retrograde and to form amyloselipid complexes. Such

properties can be utilized in the formation of foods with

high-resistant starch (RS) content.

Starches can also be modified chemically to impart func-

tional properties needed to produce certain qualities in

foodstuffs such as a decrease in viscosity and to improve gel

stability, mouth feel, appearance and texture, and resistance to

heat treatment. Various processes are used to modify starch,

the two most important being substitution and crosslinking.

Substitution involves etherification or esterification of a

relatively small number of hydroxyl groups on the glucose

units of amylose and amylopectin. This reduces retrograda-

tion, which is part of the process of staling of bread, for

example. Substitution also lowers gelatinization temperature,

provides freezethaw stability and increases viscosity. Cross-

linking involves the introduction of a limited number of

linkages between the chains of amylose and amylopectin. The

process reinforces hydrogen bonding, which occurs within the

granule. Crosslinking increases gelatinization temperature,

improves acid and heat stability, inhibits gel formation and

controls viscosity during processing. Altering the chemical

nature of starch can lead to it becoming resistant to digestion.

NSPs

NSPs are the non-a-glucan polysaccharides of the diet(Table 1). They are essentially macromolecules consisting

of a large number of monosaccharides (glycose) residues

joined to each other by glycosidic linkages (IUB-IUPAC and

Joint Commission on Biochemical Nomenclature, 1982) and


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are principally found in the plant cell wall. The term NSP was

first proposed at a meeting sponsored by the European

Economic Community Committee on Medical Research in

Cambridge in December 1978. The meeting was convened to

discuss the results of the analysis of nine foods for dietary

fibre by a number of different methods in use in laboratories

around the world. The proposal was made because An

accurate chemical identification of polysaccharides in the

diet is the first priorityy (James and Theander, 1981). Atthe meeting, the first NSP values, measured as the sum of

constituent sugars, were presented for a selection of the

test samples (James and Theander, 1981). NSPs are the most

diverse of all the carbohydrate groups and comprise a

mixture of many molecular forms, of which cellulose, a

straight chain b14-linked glucan (DP 103106) is the mostwidely distributed. Because of its linear, unbranched nature,

cellulose molecules are able to pack closely together in a

three-dimensional latticework forming microfibrils. These

form the basis of cellulose fibres, which are woven into the

plant cell wall and give it structure. Cellulose comprises

between 10 and 30% of the NSP in foods (Holland et al.,

1988, 1991a, 1992).

In contrast, the hemicelluloses are a large group of

polysaccharide hetero polymers, which contain a mixture

of hexose (6C) and pentose (5C) sugars, often in highly

branched chains. Mostly, they comprise a backbone of xylose

sugars with branches of arabinose, mannose, galactose and

glucose and have a DP of 150200. Typical of the hemi-

celluloses are the arabinoxylans found in cereals. About half

of hemicelluloses contain uronic acids, which are carboxy-

lated derivatives of glucose and galactose. They are impor-

tant in determining the properties of hemicelluloses,

behaving as carboxylic acids and are able to form salts with

metal ions such as calcium and zinc.

Common to all cell walls is, pectin, which is primarily a

14b-D galacturonic acid polymer, although 1025% othersugars such as rhamnose, galactose and arabinose, may also

be present as side chains. Between 3 and 11% of the uronic

acids have methyl substitutions, which improve the gel-

forming properties of pectin, as used in jam making. Some

residues are acetylated. Calcium and magnesium complexes

with uronic acids are characteristic of pectins.

Chemically related to the cell wall NSP, but not strictly cell

wall components, are the plant gums and mucilages. Plant

gums are sticky exudates that form at the sites of injuries to

plants. Many are highly branched complex uronic acid

containing polymers, such as Gum Arabic, named after the

Arabian port from which it was originally exported to Europe.

It comes from the Acacia tree and is one of the better known

plant gums, being sold commercially as an adhesive and used

in the food industry as a thickener and to retard sugar

crystallization. Other plant gums include karaya (sterculia),

guar, locust bean gum, xanthan and tragacanth, all of which

are licensed food additives (Saltmarsh, 2000).

Plant mucilages are botanically distinct in that they are

usually mixed with the endosperm of storage carbohydrates

of seeds. Their role is to retain water and prevent desiccation.

They are neutral polysaccharides like the hemicelluloses, of

which guar gum, from the cluster bean (Cyamopsis tetra-

gonolobus), and carob gums are similar 14b-D galactoman-nans with 16a-galactose single-unit side chains. Again, theyare widely used in the food and pharmaceutical industries as

thickeners and stabilizers in mayonnaise, soups and tooth-

pastes.

The algal polysaccharides, which include carageenan, agar

and alginate, are all NSP extracted from seaweeds or algae.

They replace cellulose in the cell wall and have gel-forming

properties. Carageenan and agar, are highly sulphated and

the ability of carageenan to react with milk protein has led to

its use in dairy products and chocolate.

Up-to-date values for the NSP content of foods are

published (Food Standards Agency/Institute of Food

Research, 2002).

Terminology based on physiology

In classifying dietary carbohydrate by its chemistry, the

principal challenge is to reconcile the various chemical

divisions with those that reflect physiology and health. A

classification based purely on chemistry does not allow a

simple translation into nutritional benefits since each of

the major chemical classes of carbohydrate has a variety of

overlapping physiological effects (Table 3). Terminology

based on physiological properties helps to focus on the

potential health benefits of carbohydrate, and identify foods

that are likely to be part of a healthy diet. But, as can be seen

from Table 4, each physiological or health benefit of

carbohydrate is attributable to several subgroups from the

main classification (Table 1). Moreover, this approach is

always open to the possibility of extensive revision, as new

physiological properties of dietary carbohydrates become

known. For example, the concept of prebiosis has added a

new dimension to understanding of how carbohydrates

behave in both the small and large intestines.

The physiology of carbohydrate can vary among indivi-

duals and populations. The classic example is lactose, which

is poorly hydrolysed by the small bowel mucosa of all adults

except Caucasians, most of whom retain the ability to digest

lactose into adult life. Additionally, within any simple

chemical group of carbohydrate, for example polyols, wide

variation in absorption may occur, ranging from almost

complete absorption of erythritol, to complete lack of

absorption of lactitol (Livesey, 2003). Similarly, starch may

have a variety of fates in the gut depending on granule

structure, whether raw or cooked and subsequent processing,

for example freezing (Stephen et al., 1983; Englyst et al.,

1992; Silvester et al., 1995). Furthermore, terminology based

on physiological properties alone provides the analyst with

an impossible target.

This dichotomy has led to the introduction of a number of

terms to describe various fractions and subfractions of


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carbohydrate and these are listed in Table 5. However, the

problems are by no means insurmountable in reconciling

these different objectives for classification. With a sound

chemical identification for all the carbohydrates, it is then

possible to group them according to their health and

physiological effects.

Prebiotics

A prebiotic is a non-digestible food ingredient that benefi-

cially affects the host by selectively stimulating the growth

and/or activity of one of a limited number of bacteria in the

colon, and thus improves host health (Gibson and Roberfroid,

1995; Gibson et al., 2004).

As a group, prebiotics are thus defined by a single

physiological parameter, although this is by no means itself

clearly established (Macfarlane et al., 2006). Analytically

they cross the boundaries between disaccharides and

polysaccharides (DPX10) (van Loo et al., 1995). It is likelyin the future that a wider spectrum from the point of DP and

molecular form of carbohydrates will be shown to be

prebiotic. Prebiotic carbohydrates have unexpected proper-

ties in the gut in that they alter the balance of the gut

microflora towards what is considered to be a more healthy

one (Macfarlane et al., 2006). They have been shown to

increase calcium absorption and bone mineral density in

adolescents. (Elia and Cummings, 2007; prebiotics are dealt

with in more detail in the accompanying paper on

Physiology).

Resistant starch

RS is the sum of starch and products of starch digestion (such

as maltose, maltotriose and a-limit dextrins) that are notabsorbed in the small bowel (Englyst et al., 1992; Champ

et al., 2003). All unmodified starch, if solubilized, can be

hydrolysed by pancreatic a-amylase. However, the rate andextent to which starch is broken down is altered by a number

of physical and chemical properties. This has led to a

classification of RS that is now widely used (Englyst and

Cummings, 1987).

RS can be fractionated into four types:

RS I: physically inaccessible starch mostly present inwhole grains

Table 3 Principal physiological properties of dietary carbohydrates

Provideenergy

Increasesatiety

Glycaemica Cholesterollowering

Increase calciumabsorption

Source ofSCFAb

Alter balanceof microflora(prebiotic)

Increase stooloutput

Immunomodulatory

Monosaccharides | |Disaccharides | | |Polyols | |c |Maltodextrins | |Oligosaccharides(non-a-glucan)

| | | | |

Starch | | |d |d

NSP | | |e | |

aProvides carbohydrate for metabolism (FAO, 1998).bShort chain fatty acids.cExcept erythritol.dResistant starch.eSome forms of non-starch polysaccharide (NSP) only.

Table 4 Physiological/health groupings of dietary carbohydrate

Glycaemica Glucose, fructose, galactose, sucrose, lactose,maltose, trehalose, maltodextrins, starch

Non-glycaemic Polyols, oligosaccharides (non-a-glucan), resistantand modified starches, NSP

Increase stooloutput

Polyols (except erythritol), some starches, NSP,lactose (in some populations), fructose (if taken inlarge amounts)

No effect on stoolweight

Glucose, galactose, sucrose, maltose, trehalose,maltodextrins, oligosaccharides, most starches

NSP, non-starch polysaccharide.aDefined as in Table 2.

Table 5 Preferred terminology of dietary carbohydrates

Chemical Physiological/botanical

Useful MonosaccharidesDisaccharidesPolyolsTotal sugarsShort-chaincarbohydratesOligosaccharidesPolysaccharidesStarchNon-starchpolysaccharidesTotal carbohydrate

PrebioticResistant starchDietary fibrea

Glycaemic

Lessuseful

SugarsSugarFree sugarsRefined sugarsAdded sugarsExtrinsic and intrinsicsugars

Non-digestible oligosaccharidesSoluble and insoluble fibreAvailable and unavailablecarbohydrateComplex carbohydrate

aIntrinsic plant cell wall polysaccharides.


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RS II: RS granules (Type B) RS III: retrograded starch (after food processing) RS IV: modified starches.

The observation that the rate and extent of starch

digestion can vary has been one of the most important

developments in our understanding of carbohydrates in the

past 30 years. There are implications of this for the glycaemic

response to foods, for fermentation in the large bowel and

for conditions such as diabetes and obesity. Methods have

been devised to measure these starch fractions in the

laboratory (Champ et al., 2003).

Dietary fibre

The term fibre, or dietary fibre, has many different meanings

in the nutrition world. It is not a precise reference to a

chemical component, or components, of the diet, but is

essentially a physiological concept as embodied in the

original definition by Trowell, the proportion of food which

is derived from the cellular walls of plants which is digested

very poorly in human beings (Trowell, 1972).

The dietary fibre hypothesis was one of the most compel-

ling in nutrition and public health in the latter half of the

twentieth century. It provided the stimulus to a great deal of

research, for example epidemiological, physiological, analy-

tical and technical. It has been the catalyst for progress in

our understanding of the cause of a number of common

diseases, especially those of the large bowel and has given

governments and the food industry valuable targets for

healthy eating. However, in the 30 years since Trowell,

Walker, Burkitt and others first proposed the fibre hypo-

thesis, nutritional science has progressed, especially our

understanding of dietary carbohydrates and with this the

apparently unique role of fibre, essentially the plant cell wall,

in many physiological processes and in disease prevention

(Cummings et al., 2004).

Were it not for the perceived public perception that fibre is

good for you, and therefore the need to provide a value for

fibre on food labels, the term would be best consigned to the

history books. However, various national and international

bodies continue to struggle with the definition and the latest

versions of their deliberations on fibre are given in Table 6.

Common to these definitions is the concept of non-

digestibility in the small intestine.

Non-digestibility needs to be defined. If it is carbohydrate

that passes across the ileo-caecal valve, then to define it

requires complex physiological studies in humans. More-

over, it will vary widely from person to person (Stephen et al.,

1983; Englyst et al., 1992; Silvester et al., 1995; Molis et al.,

1996; Ellegard et al., 1997; Langkilde et al., 2002) and be

affected by the cooking of food, storage, chewing, ripeness

and the presence of other foods (Englyst and Cummings,

1986; Champ et al., 2003). It will include many dietary

components, for example lactose in some populations, some

polyols, some starches (RS) and NSP. There is no enforceable

method that can be used to measure this physiological

fraction of the diet.

As can be seen in the accompanying paper on the

physiology of carbohydrates (Elia and Cummings, 2007),

digestibility has an entirely different context when it is used

in the description of energy metabolism. Here it is defined as

the proportion of combustible energy that is absorbed over

the entire length of the gastrointestinal tract. It would be

useful to have these different concepts of digestion aligned.

If there is a desire to use the word fibre, then it should

always be qualified by a statement itemizing those carbohy-

drates and other substances intended for inclusion, by

which is meant carbohydrates identified in the chemical

classification table (Table 1).

At a meeting of the authors of the scientific update papers,

and other experts, convened by WHO/FAO and held in

Geneva on 1718 July 2006, the definition of dietary fibre

was discussed, including the one suggested by the US

Table 6 Some currently proposed definitions/descriptions of dietary fibre

Dietary fibre consists of nondigestible carbohydrates and lignin that are intrinsic and intact in plantsFunctional fibre consists of isolated, nondigestible carbohydrates that have beneficial physiological effects in humansTotal fibre is the sum of Dietary fibre and Added fibre (Institute of Medicine, 2001).Dietary fibre means carbohydrate polymers with a degree of polymerization (DP) not lower than 3 which are neither digested nor absorbed in the smallintestine. A degree of polymerization not lower than 3 is intended to exclude mono- and disaccharides. It is not intended to reflect the average DP of amixture. Dietary fibre consists of one or more of:K Edible carbohydrate polymers naturally occurring in the food as consumed;K carbohydrate polymers, which have been obtained from food raw material by physical, enzymatic or chemical means,K synthetic carbohydrate polymers. http://www.ccfnsdu.de/fileadmin/user_upload/PDF/ReportCCFNSDU2005.pdf

Dietary fibre should be defined to include all non-digestible carbohydrates (NDC). Lignin and other non-digestible but quantitatively minor componentsthat are associated with the dietary fibre polysaccharides and may influence their physiological properties should be included as well European FoodStandards Agency Draft Paper on Carbohydrates and Dietary Fibre (Becker and Asp, 2006).Dietary fibres are the endogenous components of plant material in the diet which are resistant to digestion by enzymes produced by humans. They arepredominantly non-starch polysaccharides and lignin and may include, in addition, associated substances (Health and Welfare Canada, 1985).Dietary fibre is the edible parts of plants or analogous carbohydrates that are resistant to digestion and absorption in the human small intestine withcomplete or partial fermentation in the large intestine. Dietary fibre includes polysaccharides, oligosaccharides, lignin, and associated plant substances.Dietary fibres promote beneficial physiological effects including laxation, and/or blood cholesterol attenuation, and/or blood glucose attenuation(American Association of Cereal Chemists, 2001).


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titleResists digestion by p amylase.

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National Academy of Sciences in 2001 and that currently

proposed by Codex (http://www.ccnfsdu.de/fileadmin/user_

upload/PDF/ReportCCNFSDU2005.pdf) (Table 6).

The experts agreed that the definition of dietary fibre

should be more clearly linked to health and, after discussion,

the following definition was proposed.

Dietary fibre consists of intrinsic plant cell wall poly-

saccharides.

The established epidemiological support for the health

benefits of dietary fibre is based on diets that contain fruits,

vegetables and whole-grain foods, for which the intrinsic

plant cell wall polysaccharides are a good marker. Although

isolated or extracted fibre preparations have been shown to

have physiological effects experimentally, these cannot be

translated into health benefits directly because the epide-

miological evidence points to fruits, vegetables and whole-

grain foods as beneficial, and in a normal diet, these

polysaccharides are part of the plant cell wall complex and

do not exist individually.

Soluble and insoluble dietary fibre

These terms arose out of the early chemistry of NSPs, which

showed that the fractional extraction of NSP could be

controlled by changing the pH of solutions. They proved

very useful in the initial understanding of the properties of

dietary fibre, allowing a simple division into those which

principally had effects on glucose and lipid absorption from

the small intestine (soluble) and those which were slowly

and incompletely fermented and had more pronounced

effects on bowel habit (insoluble). However, the separation of

soluble and insoluble fractions is very pH dependent, making

the link with specific physiological properties less certain.

Much insoluble fibre is completely fermented and not all

soluble fibre has effects on glucose and lipid absorption. Many

of the early studies were done with isolated gums or extracts

of cell walls, whereas these various forms of fibre exist

together mostly in intact cell walls of plants.

Nevertheless, certain fibre-rich foods effect glycaemic

control and lipid levels and have been widely used in the

management of diabetes particularly the legumes and pulses

rather than high bran products (Kiehm et al., 1976; Simpson

et al., 1979, 1981; Rivellese et al., 1980; Mann, 1984;

Chandalia et al., 2000; Giacco et al., 2000; Mann et al.,

2004). Work on the variability in glycaemic response of

different types of foods has led to the concept of the

glycaemic index (Crapo et al., 1977; Jenkins et al., 1981) and

a new area of nutritional science has been developed,

concerned with glycaemic responses to carbohydrate-

containing foods (Foster-Powell et al., 2002).

Available and unavailable carbohydrate

A major step forward conceptually in our understanding of

carbohydrates was made by McCance and Lawrence (1929)

with the division of dietary carbohydrate into available and

unavailable. In an attempt to prepare food tables for diabetic

diets, they realized that not all carbohydrates could be

utilized and metabolized, that is provide the body with

carbohydrates for metabolism. Available carbohydrate was

defined as starch and soluble sugars and unavailable as

mainly hemicellulose and fibre (cellulose). This concept

proved useful, not the least because it drew attention to the

fact that some carbohydrate is not digested and absorbed in

the small intestine but rather reaches the large bowel where

it is fermented or even excreted in faeces.

An FAO technical workshop in Rome in 2002 on Food

energymethods of analysis and conversion factors (FAO,

2003) defined available carbohydrate as that fraction of

carbohydrate that can be digested by human enzymes, is

absorbed and enters into intermediary metabolism. (It does

not include dietary fibre, which can be a source of energy

only after fermentation).

It is somewhat misleading to talk of carbohydrate as

unavailable because carbohydrate that reaches the colon is

able to provide the body with energy through fermentation

and absorption of short-chain fatty acids. There are many

properties of carbohydrate of which site of digestion is only

one. An alternative to the terms available and unavailable

today would be to describe carbohydrates either as glycaemic

(that is providing carbohydrate for metabolism) or non-

glycaemic, which is closer to the original concept of

McCance and Lawrence. However, the FAO Technical work-

shop on Food Energy in its recommendations said, Available

carbohydrate is a useful concept in energy evaluation and

should be retained. This recommendation is at odds with the

view of the expert consultation in 1997 on carbohydrates,

which endorsed the use of the term glycaemic carbohydrate

to mean providing carbohydrate for metabolism. The group

expressed concerns that glycaemic carbohydrate might be

confused or even equated with the concept of glycaemic

index, which is an index that describes the relative blood

glucose response to different available carbohydrates. The

term available seems to convey adequately the concept of

providing carbohydrate for metabolism, while avoiding this

confusion. Furthermore, in the discussion of the energy

value of carbohydrate, the terms available and unavailable

are extensively used (Elia and Cummings, 2007). On balance,

however, we would recommend glycaemic as a more precise

and measurable fraction.

Glycaemic carbohydrate

A more recently developed distinction with regard to human

health, although arising out of the original McCance and

Lawrence concept, is whether or not the carbohydrate source

does or does not directly provide carbohydrate as an

energy source following the process of digestion and

absorption in the small intestine. Carbohydrate, which

provides glucose for metabolism is referred to as glycaemic


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carbohydrate, whereas carbohydrates that pass to the

large intestine prior to being metabolized, is referred to

as non-glycaemic carbohydrate. Most mono- and di-

saccharides, some oligosaccharides (maltodextrins) and

rapidly digested starches may be classified as glycaemic

carbohydrate. Slowly digested starches are also considered

to be glycaemic carbohydrate though glucose is less

rapidly generated. The remaining oligosaccharides, NSPs

and RS are considered to be non-glycaemic carbohydrates.

Most carbohydrate-containing unprocessed foods contain

both glycaemic and non-glycaemic carbohydrate. The extent

to which carbohydrate in foods raises blood glucose

concentration compared with an equivalent amount of

reference carbohydrate has also been used as a means of

classifying dietary carbohydrate and is known as the

glycaemic index (Venn and Green, 2007). Many factors

affect the glycaemic response to carbohydrate, including the

intrinsic properties of the food and also extrinsic factors such

as the composition of the meal, the overall diet and

biological variations of the host.

Complex carbohydrates

This term was first used in the McGovern report, Dietary

Goals for the United States in 1977 (Select Committee on

Nutrition and Human Needs, 1977). It was coined largely to

distinguish sugars from other carbohydrates and in the

report denotes fruit, vegetables and whole-grains. The term

has never been formally defined and has since come to be

used to describe either starch alone, or the combination of all

polysaccharides (British Nutrition Foundation, 1990). It was

used to encourage consumption of what are considered to be

healthy foods such as whole-grain cereals, etc., but becomes

meaningless when used to describe fruits and vegetables,

which are low in starch. As a substitute term for starch it

would seem to have little merit and, in principle, it is better

to discuss carbohydrate components by using their common

chemical names.

Physical effects of carbohydrates

Aside from their chemistry, the physiological properties of

carbohydrates are also affected by the physical state of the

food. In this context, there may be a unique role for NSP in

the control of carbohydrate metabolism. The early studies of

viscosity on glucose responses pointed to the physical

properties of NSP as being important (Jenkins et al., 1978).

In a different context, the classic study of Haber et al. (1977)

with apples shows clearly that where carbohydrate, in this

case mainly glucose and fructose, is entrapped intracellularly

in plant foods, its release in the gut is slowed and blood

glucose moderated and insulin responses lowered. A unique

property of NSP, therefore, is that it forms the plant cell wall

and thus a physical structure to foods. Numerous studies

have now shown that the physical structure of starchy foods

influences the glycaemic response.

The physical structure of a food has, therefore, a role to

play in the regulation of carbohydrate metabolism. The use

of viscous-soluble NSP isolates in this context will probably

be seen as a stepping stone to understanding fibre but not

the ultimate goal. From a nutritional and analytical view

points, the intrinsic polysaccharides of the plant cell wall,

known as dietary fibre or NSP, should be viewed as a single

entity that uniquely provides physical structure to foods.

There is however a major problem in characterizing and

measuring the key physical attributes of a food that

contributes to modifying its effects.

Whole grain

The essence of the dietary recommendations in many

countries is to eat a diet high in whole grains, fruits and

vegetables and this is embodied in the WHO/FAO report on

Diet, Nutrition and the Prevention of Chronic Diseases

(WHO, 2003) in the description of population nutrient

intake goals. However, the term whole grain has several

meanings from whole of the grain through to physically

intact structures. A precise definition is clearly needed for

labelling purposes.

Whole grain comprises whole wheat, whole-wheat flour,

wheat flakes, bulgar wheat, whole and rolled oats, oatmeal,

oat flakes, brown rice, whole rye and rye flour, whole barley

and popcorn. Cornmeal is not included as it is generally

dehulled, de-branned and de-germed. Sweet corn has been

included in some analyses (Harnack et al., 2003), but is not

included in analyses from the UK, where it is considered a

vegetable (Henderson et al., 2002; Thane et al., 2005, 2007).

Foods containing added bran, but not including endosperm

or germ, are included in some analyses (Jacobs et al., 2001)

but not in others, but are not whole grains and should be

excluded. Similarly, foods which are largely whole grain, but

not entirely, such as puffed wheat, where the puffing and

toasting causes some of the outer layers to drop off are not

truly whole grain. Such foods are difficult to consider, since

they may be consumed by a considerable proportion of the

population and are indicated as whole wheat on the label of

some products but not others.

There are also problems with the definition of a whole

grain food. For labelling purposes, the Food and Drug

Administration (1999) in the United States has defined a

whole grain food as a product containing 451% wholegrain by weight per reference amount customarily consumed

per day (Seal, 2006), and this standard has been used in

some surveys to assess intake (Lang et al., 2003; Jensen et al.,

2004). However, many foods contain less whole grain than

this, but can still make a substantial contribution to total

whole-grain intake (Thane et al., 2005, 2007).

In studies by Jacobs et al. (1998) in the United States,

breakfast cereals were considered to be whole grain if the


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product contained X25% whole grain or bran y. In amore complete analysis of the United Kingdom, foods with

whole-grain contents of 10% or more were used, rather than

the cutoffs of 25 or 51%. In the UK National Diet and

Nutrition Surveys, it was found that for young people aged

418 years, intake of whole grains was underestimated by

28% if only those products with 451% whole grains wereincluded and underestimated by 15% if only those with

whole-grain content greater than 25% were included. More

recently for adults, the 51% cutoff would have under-

estimated intake by 18% for the 198687 Dietary Survey of

British Adults (Gregory et al., 1990), and 27% in the NDNS

survey of adults in 200001 (Henderson et al., 2002),

indicating not only the underestimation but that the

manner of consuming whole grains may also be changing,

with more foods with lower amounts now being consumed.

It is a considerable amount of work to determine whole-grain

content down to the 10% level, but this would include foods

like porridge, which when cooked is 90% water but is

consumed in substantial quantities in parts of the world

(Thane et al., 2007), and which may have important health

benefits.

In his editorial comment on the 1998 Jacobs paper,

Willett (1998) remarks The physical form of whole grains

can vary from intact kernels (for which we should probably

reserve the term whole grain) to finely milled flour (whole

grain flour). This distinction between intact whole grains or

physically disrupted, although present in the food in its

entirety, is important. Grain structure affects the glycaemic

response to food (Foster-Powell et al., 2002) and high intakes

of whole-grain foods protect against the development of type

II diabetes (Venn and Mann, 2004) and cardiovascular

disease (Seal, 2006), yet we know little about the physical

form of grains in these studies.

It is also worth noting that the type of grain contributing

to whole grains may vary from country to country. For the

UK, about 90% of the whole-grain intake is wheat (Thane

et al., 2005), while in the United States, a larger proportion is

likely to be from oats, given the popularity of whole-grain

oat cereals. With the different physical and physiological

properties of these two grains, such differences need to be

taken into account when interpreting health impacts of

whole-grain consumption.

Conclusions

(1) Dietary carbohydrates should be classified according to

their chemical form, as recommended at the 1997 FAO/

WHO Expert Consultation.

(2) The physiological and health effects of carbohydrates are

dependent not only on their primary chemical form but

also on their physical properties, which include water

solubility, gel formation, crystallization state, association

with other molecules and aggregation into the complex

structures of the plant cell wall.

(3) Total carbohydrate in food should be determined by

direct measurement rather than by difference.

(4) Many terms exist to describe sugars in the diet. The most

useful are total sugars and their division into mono- and

disaccharides. The use of other terms creates difficulties

for the analyst, confusion for the consumer and suggests

properties of foods that are not related to sugars

themselves, but to the food matrix.

(5) Because neither chemical nor physical description of

carbohydrates directly reflects their physiological pro-

perties and health benefits, a number of terms to

describe carbohydrates, based on their physiology, have

been created. Of these prebiotic, glycaemic, RS and

dietary fibre are useful.

(6) Dietary fibre should be defined to reflect the health

benefits of a diet rich in fruits, vegetables and whole

grains and not the variable physiological properties or

health effects of the various carbohydrate types. The

definition proposed by the group was intrinsic plant cell

wall polysaccharides.

(7) The effects of foods containing different types of fibre on

glycaemic control and lipid levels should be investigated

further to determine the exact properties needed for

their effects. The distinction between soluble and

insoluble forms of fibre is inappropriate since the

separation is pH dependent and does not reflect the

physiological properties of whole foods in the gut.

(8) The term whole grains should be defined more clearly

and the role of intact versus milled grains established.

The whole-grain concept, along with fresh fruits and

vegetables is central to a healthy diet message.

Acknowledgements

The authors thank Professor Ingvar Bosaeus, Dr Barbara

Burlingame, Professor Jim Mann, Professor Timothy Key,

Professor Carolyn Summerbell, Dr Bernard Venn and Dr

Martin Wiseman for the valuable comments they provided

on the earlier manuscript.

Conflict of interest

During the preparation and peer review of this paper in 2006,

the authors and peer reviewers declared the following

interests.

Authors

Professor John H Cummings: Chairman, Biotherapeutics

Committee, Danone; Member, Working Group on Foods

with Health Benefits, Danone; funding for research work at

the University of Dundee, ORAFTI (2004).

Dr Alison M Stephen: Contract with World Sugar Research

Organization on trends in intakes of sugars and sources in

the diet (contract is with MRC-Human Nutrition Resource);

contracts with Cereal Partners UK on whole-grain intakes in

the UK and relationship to adiposity (contract was with


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MRC-Human Nutrition Resource); Adviser to Audrey Eyton

on scientific content on book F2 Diet; Scientific Advisory

Panel of Canadian Sugar Institute (not for profit but funded

by sugar industry) (19952002).

Peer-reviewers

Professor Ingvar Bosaeus: none declared.

Dr Barbara Burlingame: none declared.

Professor Jim Mann: none declared.

Professor Timothy Key: none declared.

Professor Carolyn Summerbell: none declared.

Dr Bernard Venn: none declared.

Dr Martin Wiseman: none declared.

References

American Association of Cereal Chemists (2001). The definition ofdietary fibre. Cereal Foods World 46, 112126.

Asp N-G (1995). Classification and methodology of food carbohy-drates as related to nutritional effects. Am J Clin Nutr 61 (Suppl 4),S980S987.

Atwater WO, Woods CD (1986). The Chemical Composition ofAmerican Food Materials. Experiment Station Bulletin no. 28. USOfficial Experiment Stations: Washington, DC.

Becker W, Asp N-G (2006). Carbohydrates and dietary fibre.British Nutrition Foundation (1990). Complex Carbohydrates in Foods:

Report of the British Nutrition Foundations Task Force. Chapman andHall: London.

Champ M, Langkilde AM, Brouns F, Kettlitz B, Le Bail-Collet Y(2003). Advances in dietary fibre characterization. 2. Consump-tion, chemistry, physiology and measurement of resistant starch;implications for health and food labelling. Nutr Res Rev 16,143161.

Chandalia M, Garg A, Lutjohann D, von Bergmann K, Grundy SM,Brinkley LJ (2000). Beneficial effects of high dietary fiber intake inpatients with type 2 diabetes mellitus. N Engl J Med 342, 13921398.

Crapo PA, Reaven G, Olefsky J (1977). Postprandial plasma-glucoseand insulin responses to different complex carbohydrates. Diabetes26, 11781183.

Cummings JH, Englyst HN (1995). Gastrointestinal effects of foodcarbohydrate. Am J Clin Nutr 61, 938S945S.

Cummings JH, Edmond LM, Magee EA (2004). Dietary carbohydratesand health: do we still need the fibre concept? Clin Nutr Suppl 1,517.

Cummings JH, Macfarlane GT, Englyst HN (2001). Prebiotic diges-tion and fermentation. Am J Clin Nutr 73, 415S420S.

Cummings JH, Roberfroid MB, Andersson H, Barth C, Ferro-Luzzi A,Ghoos Y et al. (1997). A new look at dietary carbohydrate:chemistry, physiology and health. Eur J Clin Nutr 51, 417423.

Department of Health (1989). Dietary Sugars and Human Disease. HerMajestys Stationery Office: London.

Elia M, Cummings JH (2007). Physiological aspects of energymetabolism and gastrointestinal effects of carbohydrates. Eur JClin Nutr 61 (Suppl 1), S40S74.

Ellegard L, Andersson H, Bosaeus I (1997). Inulin and oligofructosedo not influence the absorption of cholesterol, or the excretion ofcholesterol, Ca, Mg, Zn, Fe, or bile acids but increases energyexcretion in ilesotomy subjects. Eur J Clin Nutr 51, 15.

Englyst HN, Cummings JH (1986). Digestion of the polysaccharidesof banana (Musa paradisiaca sapientum) in man. Am J Clin Nutr 44,4250.

Englyst HN, Cummings JH (1987). Resistant starch, a new foodcomponent: a classification of starch for nutritional purposes. In:

Morton ID (ed). Cereals in a European Context. Ellis Horwood:

Chichester. pp 221233.Englyst HN, Kingman SM, Cummings JH (1992). Classification and

measurement of nutritionally important starch fractions. Eur J Clin

Nutr 46, S33S50.Englyst HN, Quigley ME, Hudson GJ (1994). Determination of

dietary fibre as non-starch polysaccharides with gasliquid

chromatographic, high-performance liquid chromatographic or

spectrophotometric measurement of constituent sugars. Analyst

119, 14971509.Englyst K, Liu S, Englyst H (2007). Nutritional characterisation and

measurement of dietary carbohydrates. Eur J Clin Nutr 61 (Suppl 1),S19S39.

European Communities (1990). Council directive 90/496/EEC on

nutrition labelling for foodstuffs.European Communities (2000). Council directive 2000/13/EC on the

approximation of the laws of the member states relating to the

labelling, presentation and advertising of foodstuffs.FAO (1998). Carbohydrates in human nutrition. Food and Agriculture

Organization of the United Nations: Rome. Report of a Joint FAO/

WHO Expert Consultation. FAO Food and Nutrition Paper no. 66.FAO (2003). Food EnergyMethods of Analysis and Conversion Factors.

Food and Agriculture Organization of the United Nations: Rome.

Report of a Technical Workshop. FAO Food and Nutrition Paper

no. 77.Food and Drug Administration (1993). Food labelling: mandatory

status of nutrition labelling and nutrient content revision, format

for nutrition label. Fed Regist 58, 20792228.Food and Drug Administration (1999). Health claim notification for

whole grain foods. http://www.cfsan.fda.gov/Bdms/flgrains.html.Food Standards Agency/Institute of Food Research (2002). The

Composition of Foods Sixth Summary Edition. Royal Society of

Chemistry: Cambridge.Foster-Powell K, Holt SHA, Brand-Miller JC (2002). International

table of glycemic index and glycemic load values: 2002. Am J Clin

Nutr 76, 556.Galliard TE (1987). Starch: Properties and Potential. John Wiley & Sons:

Chichester.Giacco R, Parillo M, Rivellese AA, Lasorella G, Giacco A, DEpiscopo L

et al. (2000). Long-term dietary treatment with increased amounts

at fiber-rich low-glycemic index natural foods improves blood

glucose control and reduces the number of hypoglycemic events

in type 1 diabetic patients. Diabetes Care 23, 14611466.Gibson GR, Roberfroid M (1995). Dietary modulation of the human

colonic microbiota: introducing the concept of prebiotics. J Nutr

125, 14011412.Gibson GR, Probert HM, Van Loo J, Rastall RA, Roberfroid M (2004).

Dietary modulation of the human colonic microbiotia: updating

the concept of prebiotics. Nutr Res Rev 17, 259275.Gibson SA (2000). Breakfast cereal consumption in young children:

associations with non-milk extrinsic sugars and caries experience:

further analysis of data from the UK national diet and nutrition

survey of children aged 1.54.5 years. Public Health Nutr 3, 227232.Gregory J, Foster K, Tyler H, Wiseman M (1990). Dietary and

Nutritional Survey of British Adults. Her Majestys Stationery Office:

London.Haber GB, Heaton KW, Murphy D, Burroughs LF (1977). Depletion

and disruption of dietary fibre: effects on satiety, plasma-glucose

and serum insulin. Lancet ii, 679682.Harnack L, Walters SA, Jacobs Jr DR (2003). Dietary intake and food

sources of whole grains among US children and adolescents: data

from the 19941996 continuing survey of food intakes by

individuals. J Am Diet Assoc 103, 10151019.Health Canada (2005). Canadian nutrient file. http://www.hc-sc.

gc.ca/fn-an/nutrition/fiche-nutri-data/index_e.html.Health and Welfare Canada (1985). Report of the Expert Advisory

Committee a Dietary Fibre.


S16


Henderson L, Gregory J, Swan G (2002). The National Diet & NutritionSurvey: Adults Aged 19 to 64 Years. Vol. 1: Types and Quantities ofFood Consumed. Her Majestys Stationery Office: London.

Hidaka H, Eida T, Takizawa T, Tokunaga T, Tashiro Y (1986). Effects offructooligosaccharides on intestinal flora and human health.Bifidobacteria Microflora 5, 3750.

Holland B, Unwin ID, Buss DH (1992). Fruit and Nuts. First Supplementto 5th Edition of McCance and Widdowsons the Composition of Foods.Her Majestys Stationery Office: London.

Holland B, Unwin ID, Buss DH (eds) (1988). Cereals and CerealProducts. Royal Society of Chemistry: Cambridge.

Holland B, Unwin ID, Buss DH (eds) (1991a). Vegetables, Herbs andSpices. Royal Society of Chemistry: Cambridge.

Holland B, Welch AA, Unwin ID, Buss DH, Paul AA, Southgate DAT(1991b). McCance & Widdowsons the Composition of Foods. HerMajestys Stationery Office: London.

Hoover R, Sosulski FW (1991). Composition, structure, functionality,and chemical modification of legume starches: a review. Can JPhysiol Pharmacol 69, 7992.

http://www.britannica.com/eb/article-9057022/oligosaccharide.http://www.ccnfsdu.de/fileadmin/user_upload/PDF/ReportCCNFSDU

2005.pdf.Institute of Medicine (2001). Dietary Reference Intakes for Energy,

Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein and AminoAcids. National Academy Press: Washington, DC.

IUBIUPAC Joint Commission on Biochemical Nomenclature (1982).Abbreviated terminology of oligosaccharide chains. J Biol Chem257, 33473351.

IUPACIUB Joint Commission on Biochemical Nomenclature (1996).Nomenclature of carbohydrates. www.chem.qmul.ac.uk/iupac/2carb/.

Jacobs Jr DR, Meyer HE, Solvoll K (2001). Reduced mortality amongwhole grain bread eaters in men and women in the Norwegiancounty study. Eur J Clin Nutr 55, 137143.

Jacobs Jr DR, Meyer KA, Kushi LH, Folsom AR (1998). Whole-grainintake may reduce the risk of ischemic heart disease death inpostmenopausal women: the Iowa womens health study. Am JClin Nutr 68, 248257.

James WPT, Theander O (eds) (1981). The Analysis of Dietary Fibre inFood. Marcel Dekker: New York. p 259.

Jenkins DJ, Wolever TM, Leeds AR, Gassull MA, Haisman P, Dilawari Jet al. (1978). Dietary fibres, fibre analogs, and glucose-tolerance-importance of viscosity. Br Med J 1, 13921394.

Jenkins DJ, Wolever TM, Taylor RH, Barker H, Fielden H, Baldwin JMet al. (1981). Glycemic index of foods: a physiological basis forcarbohydrate exchange. Am J Clin Nutr 34, 362366.

Jensen MK, Koh-Banerjee P, Hu FB, Franz M, Sampson L, Gr+nbk Met al. (2004). Intakes of whole grains, bran, and germ and the risk ofcoronary heart disease in men. Am J Clin Nutr 80, 14921499.

Kelly SA, Summerbell C, Rugg-Gunn AJ, Adamson A, Fletcher E,Moynihan PJ (2005). Comparison of methods to estimate non-milk extrinsic sugars and their application to sugars in the diet ofyoung adolescents. Br J Nutr 94, 114124.

Kennedy G, Burlingame B (2003). Analysis of food composition dataon rice from a plant genetic resources perspective. Food Chem 80,589596.

Kiehm TG, Anderson JW, Ward K (1976). Beneficial effects of a highcarbohydrate, high fiber diet on hyperglycemic diabetic men. Am JClin Nutr 29, 895899.

Kunz C, Rudloff S, Baier W, Klein N, Strobel S (2000). Oligosaccha-rides in human milk: structural, functional, and metabolic aspects.Annu Rev Nutr 20, 699722.

Lang R, Thane CW, Bolton-Smith C, Jebb SA (2003). Consumption ofwhole-grain foods by British adults: findings from further analysisof two national dietary surveys. Public Health Nutr 6, 479484.

Langkilde AM, Champ M, Anderson H (2002). Effects of high-resistant-starch banana flour (RS2) on in vitro fermentation andthe small-bowel excretion of energy, nutrients, and sterols: anileostomy study. Am J Clin Nutr 75, 104111.

Livesey G (2003). Health potential of polyols as sugar replacers, withemphasis on low glycaemic properties. Nutr Res Rev 16, 163191.

Macfarlane S, Macfarlane GT, Cummings JH (2006). Prebiotics in thegastrointestinal tract. Aliment Pharmacol Ther 24, 701714.

Mann J (1984). Lines to legumes: changing concepts of diabetic diets.Diabet Med 1, 191198.

Mann J, De Leeuw I, Hermansen K, Karamanos B, Karlstrom B,Katsilambros N et al. (2004). Evidence-based nutritional ap-proaches to the treatment and prevention of diabetes mellitus.Nutr Metab Cardiovasc Dis 14, 373394.

McCance RA, Lawrence RD (1929). The Carbohydrate Content of Foods.Her Majestys Stationery Office: London.

Molis C, Flourie B, Ouarne F, Gailing MF, Lartigue S, Guibert A et al.(1996). Digestion, excretion and energy value of fructooligosac-charides in healthy humans. Am J Clin Nutr 64, 324328.

National Academy of Sciences (2001). Dietary References Intakes.Proposed Definition of Dietary Fiber. National Academy of Sciences:Washington DC.

New Zealand Nutrition Foundation (2004). Sugar and our diet.http://www.chelsea.co.nz/shared/documents/report.pdf.

Oku T, Tokunaga T, Hosoya N (1984). Non-digestibility of a newsweetener Neosugar in the rat. J Nutr 114, 15741581.

Pehrsson PR, Cutrufelli RL, Gebhardt SE, Lemar LE, Holcomb GT,Haytowitz DB et al. (2005). USDA database for the added sugarscontent of selected foods. www.ars.usda.gov/nutrientdata.

Prosky L, Asp N-G, Schweizer TF, De Vries JW, Furda I (1992).Determination of insoluble and soluble dietary fiber in foods andfood products: collaborative study. J AOAC Int 75, 360367.

Regina A, Bird A, Topping D, Bowden S, Freeman J, Barsby T et al.(2006). High-amylose wheat generated by RNA interferenceimproves indices of large-bowel health in rats. Proc Natl Acad SciUSA 103, 35463551.

Rivellese A, Riccardi G, Giacco A, Pacioni D, Genovese S, Mattioli PLet al. (1980). Effect of dietary fibre on glucose control and serum-lipoproteins in diabetic-patients. Lancet 2, 447450.

Roberfroid M (2005). Inulin-type Fructans. Functional Food Ingredients.CRC Press: Boca Raton.

Roberfroid M, Gibson GR, Delzenne N (1993). The biochemistry ofoligofructose, a non-digestible fiber: an approach to calculate itscaloric value. Nutr Rev 51, 137146.

Saltmarsh ME (2000). Essential Guide to Food Additives. LeatherheadPublishing: Leatherhead.

Seal CJ (2006). Whole grains and CVD risk. Proc Nutr Soc 65, 2434.Select Committee on Nutrition and Human Needs (1977). Dietary

Goals for the United States. US Government Printing Office:Washington, DC.

Silvester KR, Englyst HN, Cummings JH (1995). Ileal recovery ofstarch from whole diets containing resistant starch measuredin vitro and fermentation of ileal effluent. Am J Clin Nutr 62,403411.

Simpson HC, Simpson RW, Lousley S, Carter RD, Geekie M,Hockaday TD et al. (1981). A high-carbohydrate leguminous fiberdiet improves all aspects of diabetic control. Lancet 1, 15.

Simpson RW, Mann JI, Eaton J, Carter RD, Hockaday TD (1979).High-carbohydrate diets and insulin dependent diabetics. Br Med J2, 523525.

Southgate DAT (1978). Free sugars in foods. J Hum Nutr 32, 335347.Southgate DAT (1991). Determination of Food Carbohydrates. Elsevier

Science Publishers Ltd: Barking.Southgate DAT (1995). Digestion and metabolism of sugars. Am J Clin

Nutr 62 (Suppl 1), S203S211.Stephen AM (2006). Impact of Carbohydrate Methodology on

Dietary Intake. Copenhagen, April 2006.Stephen AM, Thane CT, Bramweh CF (2007). Sugars in the diet:

definitions, intakes and sourcesan update. (in preparation).Stephen AM, Haddad AC, Phillips SF (1983). Passage of carbohydrate

into the colon. Direct measurements in humans. Gastroenterology85, 589595.


S17


Thane CT, Jones AR, Stephen AM, Seal CJ, Jebb SA (2005). Whole-grain intake of British young people aged 418 years. Br J Nutr 94,825831.

Thane CW, Jones AR, Stephen AM, Seal CJ, Jebb SA (2007).Comparative whole-grain intake of British adults in 19867 and20001. Br J Nutr 97, 987992.

The Nordic Council (2004). Nordic Nutrition Recommendations2004, Integrating Nutrition and Physical Activity. The NordicCouncil of Ministers, The Nordic Food Policy Co-Operation.Copenhagen.

Trowell H (1972). Dietary fibre and coronary heart disease. Eur J ClinBiol Res 17, 345349.

United States Department of Agriculture (2007): http://www.ars.usda.gov/nutrientdata.

van Loo J, Coussement P, de Leenheer L, Hoebregs H, Smits G(1995). On the presence of inulin and oligofructose as

natural ingredients in the western diet. Crit Rev Food Sci Nutr 35,525552.

Venn BJ, Green TJ (2007). Glycemic index and glycemic load:measurement issues and their effect on dietdisease relationships.Eur J Clin Nutr 61 (Suppl 1), S122S131.

Venn BJ, Mann JI (2004). Cereals grains, legumes and diabetes. Eur JClin Nutr 58, 14431461.

Ward RE, Ninonuevo M, Mills DA, Lebrilla CB, German JB (2006). Invitro fermentation of breast milk oligosaccharides by Bifidobacter-ium infantis and Lactobacillus gasseri. Appl Environ Microbiol 72,44974499.

WHO (2003). Diet, Nutrition and the Prevention of Chronic Diseases.Report of a Joint WHO/FAO Expert Consultation. WHO TechnicalReport Series no. 916. World Health Organization: Geneva.

Willett WC (1998). The dietary pyramid: does the foundation needrepair? Am J Clin Nutr 68, 218219.


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Carbohydrate terminology and classificationIntroductionClassificationTerminologyTotal carbohydrateSugarsTotal sugarsFree sugarsAdded sugarsExtrinsic and intrinsic sugarsIntrinsic sugarsExtrinsic sugarsNon-milk extrinsic sugars

Oligosaccharides, short-chain carbohydratesMilk oligosaccharidesStarch and modified starchModified starch

NSPsTerminology based on physiologyPrebioticsResistant starchDietary fibre

Soluble and insoluble dietary fibreAvailable and unavailable carbohydrateGlycaemic carbohydrateComplex carbohydratesPhysical effects of carbohydratesWhole grainConclusionsTable 1 The major dietary carbohydratesTable 2 Energy and macronutrient intakes for 52 weighed records analysed using Canadian and UK food tablesTable 3 Principal physiological properties of dietary carbohydratesTable 4 Physiological/health groupings of dietary carbohydrateTable 5 Preferred terminology of dietary carbohydratesTable 6 Some currently proposed definitions/descriptions of dietary fibreAcknowledgementsReferences

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