Chapter4 %Carbohydrates:%Simple%Sugars%and% …...2/16/16 1 Chapter4%...

transcript

2/16/16

Chapter 4 Carbohydrates: Simple Sugars and

Complex Chains BIOL 103, Spring 2016

What Are Carbohydrates?

•  Sugars, starches, and fibers •  Major food sources: Plants – Produced during photosynthesis

•  Two main carbohydrate types – Simple (Sugars) – Complex (Starches and fibers)

Simple Sugars

•  Monosaccharides – Glucose – Fructose – Galactose

Monosaccharides

•  Glucose/Dextrose – Most abundant simple sugar in nature – Gives food a mildly sweet flavor – Usually joined to another sugar in foods to form disaccharides, starch, dietary fiber – Provides energy to body cells • Blood sugar levels • Only fuel source used by brain

2/16/16

Monosaccharides

•  Fructose/Levulose – “fruit sugar” – Tastes the sweetest of all the sugars – Occurs naturally in fruits and vegetables – Found in fruits, vegetables, honey, and corn syrup

High Fructose Corn Syrup

•  Why do we use it? – Before 1970s à U.S. cane sugar à too expensive

– 1980s, food companies switched to cheaper corn • Pepsi/Coke switched in 1984

High Fructose Corn Syrup

•  How is it made? 1.  Convert glucose à fructose, using isomerase 2.  Add corn syrup, then a specific ra]o of

glucose • Example: HFCS 55 (so` drinks)

Why is High Fructose Corn Syrup associated with weight gain?

1.  Corn is cheap à cheaper soda à supersize à drink more à more calories

2.  Fructose does NOT release insulin and lep:n à does not feel full à drink more à more calories

•  However, note that overconsump]on of ANY forms of sugar will contribute to weight gain.

2/16/16

Monosaccharides

•  Galactose – Rarely occurs as a monosaccharide in food – Usually bonds to glucose to form lactose • Primary sugar in milk and dairy products

Simple Sugars

•  Disaccharides: Consist of two monosaccharides linked together – Sucrose: glu + fru – Lactose: glu + gal – Maltose: glu + glu

•  Linked by glycosidic bonds

Disaccharides

•  Sucrose: glucose + fructose – “Table sugar” – Made from sugar cane and sugar beets – Listed as sugar on food labels

•  Lactose: glucose + galactose – “Milk sugar” – Found in milk and milk products

Lactose Intolerance

•  Who has it? – Anyone who does not have enough lactase, which normally converts (lactose à glucose + galactose)

•  Why do you get it? – Lactase nonpersistence (most common) –  Injury/infec]on to intes]ne usually during infancy – Developmental lactase deficiency in premature infants

– Congenital lactase deficiency: rare gene]c disorder from birth

2/16/16

Disaccharides

•  Maltose: glucose + glucose – “Malt sugar” – Seldom occurs naturally in foods – Product of starch breakdown – Found in germina]ng cereal grains

Complex Carbohydrates •  Chains of three or more sugar molecules – Oligosaccharides •  3-‐10 sugar molecules •  Examples sources: dried beans, peas, and len]ls

–  Polysaccharides •  Long chains of monosaccharides •  Structural differences affect how they behave in water and with hea]ng •  Diges]ble (e.g. starch) or nondiges]ble (e.g. fiber)

Complex Carbohydrates

•  Starch – Storage form of energy in plants – Found in grains, legumes, and tubers (potatoes and yams) – Long chains of glucose units • Amylose—straight chains • Amylopec:n—branched chains – Digested more rapidly than amylose

– Resistant starch: A starch that is not digested

2/16/16

•  Glycogen – Storage form of carbohydrates in animals – Highly branched chains of glucose units – Blood glucose – Most stored in our skeletal muscle and liver – Carbohydrate “loading”

•  Fiber – Nondiges]ble carbohydrates and lignins – Dietary fiber: soluble + insoluble fiber • Fruits, vegetables, legumes, and whole grains

– Func:onal fiber: Isolated and added to foods – Total fiber: Sum of dietary fiber and func]onal fiber

Types of Dietary Fiber

Soluble •  Dissolves in water à gel-‐

like à slows diges]on, lowers blood cholesterol and glucose levels

•  Fermentable •  Example: Fruits, vegetables,

legumes, oats, oat bran, legumes (dried beans and peas)

Insoluble •  Does not dissolve in water

à creates a bulk à larger, so`er stool

•  Fermentable (Resistant Starch) vs. Non-‐fermentable

•  Example: Bran por]on of whole grains, skins of fruits/vegetables, cauliflower, potato skins

2/16/16

Complex Carbohydrates (Dietary Fiber)

•  Gums and mucilages – Gums: Gel-‐forming fibers in plant cell walls and seeds

– Mucilages: gela]nous soluble fiber found in seaweed

•  Pec:ns – “Sugar acids”; keeps fruits in shape – Dietary fiber found in all plants, especially fruits and berries

– Pec]ns + acid + sugar = jam

•  Beta-‐glucans – Polysaccharides of branched glucose units linked with beta glycosidic bonds

– Found in barley and oats – Help decrease blood cholesterol levels

•  Lignin: – Non actually carbohydrates; composed of mul]-‐ring alcohol units that compose the only non-‐carbohydrate component of dietary fiber

– Found in cell walls of woody plants and the seeds of fruits

•  Cellulose: long, straight chains of glucose molecules with beta glycosidic bonds – Structural func]on in plants: forms the woody fibers in trees and strong plant cell walls

•  Hemicelluloses: variety of monosaccharides with many branching side chains – Usually mixed with cellulose in plants – Outer bran layer in cereal grains, legumes, vegetables, nuts

Dietary Fiber

2/16/16

Carbohydrate Diges]on

•  Diges]on breaks down carbohydrates to single sugars – Mouth • Salivary amylase

– Stomach • HCl’s acidity stops the ac]on of salivary amylase à stops carbohydrate diges]on

•  Diges]on – Small intes]ne • Pancrea:c amylase con]nues starch diges]on • Brush border enzymes digest disaccharides • Other diges]ve enzymes: – Maltase, sucrase, and lactase

•  Diges]on – Bonds that link glucose molecules • Alpha bonds – Broken down by human enzymes (e.g. starch)

• Beta bonds – Bonds remain unbroken by human enzymes (e.g. cellulose, resistant starch)

2/16/16

Carbohydrate Absorp]on

•  Absorp]on in the small intes]ne – Glucose, galactose, fructose molecules travel to the liver through the portal vein – Liver converts the absorbed monosaccharaides to glucose: • Galactose à glucose • Fructose à glucose

Carbohydrates and Glucose in the Body

•  Excess glucose is stored as… – Liver glycogen (~1/3) • Maintains normal blood glucose levels

– Muscle glycogen (~2/3) • Fuels muscle ac]vity

•  Glucose is our primary fuel – To drive chemical processes – To maintain normal blood glucose levels

•  Other sources of energy: fat, protein •  What is the order of energy usage by body?

2/16/16

Consequence of Low Blood Sugar

•  Sparing body protein – Adequate carbohydrates prevent body from making glucose from body proteins

– Preven]ng ketosis • Ketone bodies à ketosis à dehydra]on • Body needs a minimum of 50 to 100 grams of carbohydrate/day to prevent ketosis

•  Regula]ng blood glucose – Hyperglycemia vs. Hypoglycemia

– Controlled by hormones: •  Insulin • Glucagon • Epinephrine (Adrenaline) – “Fight-‐or-‐flight” hormone

Regula]ng Blood Glucose

•  Glycemic Index measures effect of food on blood glucose levels – Different foods vary in their effect on blood glucose levels – Foods with High Glycemic Index cause faster and higher rise in blood glucose

2/16/16

Glycemic Index High Blood Glucose: Diabetes Mellitus

•  What is diabetes?

•  Normally: • Eat food with glucose à blood and cells •  If too much blood glucose à pancreas releases insulin à blood glucose decreases

– If you have diabetes: • Pancreas: liqle or no insulin OR cells do not respond appropriately to insulin à hyperglycemia

High Blood Glucose: Diabetes

•  Forms of diabetes mellitus: – Diabetes Type I: – Diabetes Type II: – Gesta:onal diabetes:

The Role of Carbohydrates in Our Diet

•  Cons: excess simple sugar à weight gain, poor nutrient intake, tooth decay

•  Pros: high intake of foods rich in dietary fiber offers many health benefits, including reduced risk of: – Obesity – Type 2 diabetes – Cardiovascular disease – Gastrointes]nal disorders

•  Increase fiber intake gradually while drinking plenty of fluids

2/16/16

Carbohydrates and Health

•  Fiber and obesity – Possible role in weight control

•  Fiber and type 2 diabetes – Beqer control of blood glucose

•  Fiber and cardiovascular disease – Can lower blood cholesterol levels

•  Fiber and gastrointes:nal disorders – Healthier gastrointes]nal func]oning

•  Nega]ve effects of excess fiber: – If add supplemental fiber too quickly, may have side effects: abdominal bloa]ng, gas – Can bind small amounts of minerals à prevent some mineral absorp]on • Examples: Zinc, Calcium, Iron

•  Fiber does not have UL: because ea]ng a lot of fiber (found naturally in foods) doesn’t really affect overall health of healthy people.

•  Modera]ng sugar intake – Use less added sugar – Limit so` drinks, sugary cereals, candy, ice cream, and sweet desserts – Choose fresh fruits or those canned in water

The Role of Carbohydrates in Our Diet

•  Choosing Carbohydrates Wisely – Increase fruit, vegetables, whole grains, low-‐fat milk

•  Strategies – Eat peel fruit/vegetables – Eat legumes – Choose brown rice – Choose high-‐fiber cereal – Drink plenty of water!

2/16/16

•  Nutri:ve sweeteners: – Monosaccharides, disaccharides, and sugar alcohols – Natural vs. refined

•  Non-‐nutri:ve sweeteners: – Saccharin – Aspartame – Acesulfame K – Sucralose

Nutri]ve Sweeteners

•  Nutri:ve Sweeteners: substances that sweeten food and can absorbed and yield energy in the body.

•  Types: 1.   Natural: mono + di-‐saccharides •  e.g. honey, maple syrup

2.   Refined: mono + di-‐saccharides extracted from plant food •  e.g. white sugar, fructose

3.   Sugar Alcohol/Polyols: may be sugar/sucrose free, but not always calorie free •  e.g. xylitol

Non-‐Nutri]ve Sweeteners

•  Non-‐nutri:ve sweeteners: “ar]ficial sweeteners”; yields almost no energy

•  Types: 1.   Saccharin (1970s; bladder cancer) 2.   Aspartame (phenylalanine + aspar]c acid;

PKU) 3.   Acesulfame K (stable under heat) 4.   Sucralose (used in baked goods, beverages,

gela]n, etc.)

Chapter4 %Carbohydrates:%Simple%Sugars%and% …...2/16/16 1 Chapter4%...

Documents