The Carbohydrates: Sugars, Starches, and Fibers

Chapter 4

Introduction

Brain Glucose as E source

Muscles ½ Glucose & Glycogen (storage form of glucose) ½ Fat

Sources of carbohydrates

“Fattening” – mistaken thinking

CHEMIST’S VIEW OF CARBOHYDRATES

CHO cmpds composed of C, O, H arranged as mono or multiple mono

Dietary CHOs Monosaccharide Disaccharides Polysaccharides

CHEMIST’S VIEW OF CARBOHYDRATES

CHEMIST’S VIEW OF CARBOHYDRATES

Monosaccharides – three kinds Same numbers and kinds of atoms Differ in arrangements 1.Glucose – blood sugar2.Fructose3.Galactose

CHEMIST’S VIEW OF CARBOHYDRATES

Disaccharides Pairs of three monosaccharides

1. Maltose – two glucose* units2. Sucrose – glucose* and fructose3. Lactose – glucose* and galactose

CHO-put together & taken apart by similar chemical rxns:

Condensation (to make) Links two monosaccharides together

CHO-put together & taken apart by similar chemical rxns:

Hydrolysis (to take apart) Breaks a disaccharide in two Commonly occurs during digestion

CHEMIST’S VIEW OF CARBOHYDRATES

Polysaccharides Contain many glucose units sometimes few mono strung together Three types important in nutrition: glycogen, starch, fiber.

1.Glycogen Storage form of energy Many glucose units linked Hormonal message

CHEMIST’S VIEW OF CARBOHYDRATES

2. Starch• Storage form of E (glucose) in plants• Long, branched, or unbranched glucose molecules • Consume a plant body hydrolyzes starch to glucose glucose as E• All come from plants (grains richest source)

CHEMIST’S VIEW OF CARBOHYDRATES

3. Fibers Structural part in plant; found in all plant derived

foods Differ from starches

bonds between monos can’t be broken down by digestive enzymes

Soluble fibers (dissolve in water)- form gels easily digested heart protective and diabetes

Insoluble fibers (do not dissolve in water)-3. do not form gels less readily fermented promote bowel

movement, aid constipation

Functional fibers Resistant starches Phytic acid

Carbohydrate Digestion

Ultimate goal Glucose for absorption and use**

Hydrolysis via enzymes

Mouth Salivary enzyme- amylase starch to poly to maltose

Stomach Stomach acid & protein- inactivate amylase No enzymes to significantly further breakdown Role of fiber

lingers in stomach, delaying gastric emptying fullness/satiety

Carbohydrate Digestion

Small intestine Most carbohydrate digestion Pancreatic amylase

major CHO digesting enzyme Specific disaccharide enzymes

Maltase: maltose 2glucose Sucrase: sucrose glucose + fructose Lactase : lactose glucose + galactose

Large intestine Fibers only remaining

(sugars & starches digested) Aid in healthy bowel functions/movements

Carbohydrate Absorption

Takes place in small intestine

Active transport Glucose Galactose

Facilitated diffusion Fructose

Carbohydrate Absorption

Lactose Intolerance

Lactase activity

Symptoms of intolerance

Causes of intolerance beyond age

Prevalence

Lactose Intolerance

Dietary changes Manage dairy consumption rather than restriction Fermented milk products Individualized diets Potential nutrient deficiencies

Riboflavin, vitamin D, and calcium

Carbohydrate Metabolism

Glucose is key player

Storing glucose as glycogen Liver storage Muscle storage

Carbohydrate Metabolism

Glucose for energy Fuels most of body’s cells Cellular breakdown of glucose into carbon dioxide and water

Making glucose from protein Amino acid conversion to glucose in some extent Gluconeogenesis- conversion of protein to glucose (not ideal)

Carbohydrate Metabolism

Ketone bodies from fat fragments Inadequate supply of carbohydrates

Carbohydrate needs for protein sparing and prevention of ketosis (50-100g CHO daily)

Using glucose to make fat

The Constancy of Blood Glucose

Steady supply in blood stream Intestines – food consumption Liver – glycogen breakdown

Blood glucose homeostasis Insulin Glucagon & epinephrine

Blood Glucose Homeostasis

The Constancy of Blood Glucose

Balancing within the normal range Balanced meals at regular intervals

Diabetes Blood glucose levels rises after a meal and remains above

normal levels because Insulin is either inadequate or ineffective Type 1 diabetes Type 2 diabetes

Hypoglycemia Blood glucose levels fall below normal Symptoms Seen in poorly managed diabetes, too much insulin, strenuous

exercise, inadequate food intake, or illness

The Constancy of Blood Glucose

Glycemic response Speed of glucose absorption, how high level of blood glucose rises,

and how quickly it returns to normal glucose levels Important in diabetes Low glycemic response

Desired High glycemic response Glycemic index-method of classifying food according to their

potential to raise blood glucose

Health Effects of Sugars

Pleasure in moderate amounts without harming health

Nutrient deficiencies Energy with few other nutrients (empty calories) Some sugar sources are more nutritious than other

Dental caries Bacteria in mouth ferment sugars producing an acid that erodes

tooth enamel, causing tooth decay

Practicing good oral hygiene and minimize consuming sugar and starch containing foods and beverages

Recommended Intakes of Sugars

Dietary Guidelines Choose and prepare foods with little added sugar

DRI Added sugars

No more than 25% of day’s total energy

WHO and FAO recommendations Suggest restricting consumption of added sugars to less than 10% of

total energy.

Alternative Sweeteners

Artificial sweeteners Sometimes called Non-nutritive sweeteners

Provide virtually no E Large doses and adverse effects

Stevia – an herbal product Derives from a plant Generally recognized as safe (GRAS)-used as additive in variety of food and

drinks

Sugar alcohols Found in “sugar-free” or reduced-calorie products Provide kcalories, but fewer than CHO sugars (nutritive sweetener) Benefits and side effects

Health Effects of Starch and Fibers

Heart disease Whole grains

Soluble fibers Sources Bind with bile acids in GI tract increasing excretion

Protect against heart disease and stroke

Health Effects of Starch and Fibers

Diabetes High-fiber foods

trap nutrients and delay transit time in GI tract glucose absorption slowed

GI health High-fiber foods

increase stool wt, easing passage, reduce transit time Ample fluids easier passage Protects against colon cancer

Weight management High-fiber foods and whole grains help with healthy body weight

Health Effects of Starch and Fibers

Excessive fiber Insufficient energy or nutrient needs Abdominal discomfort, gas, diarrhea GI obstruction Nutrient absorption Dietary goals

Balance, moderation, variety

Recommended Intakes of Starch & Fibers

DRI for carbohydrates 45 to 65% of energy requirement

RDA for carbohydrates 130 grams per day

Fiber DV: 11.5 grams per 1000-kcalories DRI: 14 grams per 1000-kcalories No UL