Chapter ThreeThe Carbohydrates: Sugars, Starch & Fiber

NUT SCI 242 Spring 05 © Karen Lacey, MS ,RD, CD

I. Carbohydrate Basics

Compounds composed of carbon, hydrogen, and oxygen atoms.

The primary role: energy source – 4 cal/gram

Ideal fuel for the bodyTwo types:

– Simple– Complex

II. Simple Carbohydrates

Structure: – A single sugar (Monosaccharide)– A pair of two sugars linked together

(Disaccharide)6 carbons in ring form All are chemically similar to glucose and

can be converted into glucose

A. Monosaccharides

1. Glucose “blood sugar”

used for energy Found in fruits,

vegetables, honey

2. Fructose Sugar of fruits,

honey, maple & corn syrup

Cont’d

3. GalactosePart of milk

sugar

B. Disaccharides (double sugars)

Two sugar units linked together

1. SucroseGlucose +

FructoseTable Sugar

Cont’d

1. Lactose Glucose + Galactose Milk sugar

2. Maltose Glucose + Glucose Product of starch

breakdown

After eating sugar, intestinal enzymes split the double sugars into single sugars.

C. Sugar & Health Guidelines recommend limiting

sugar in the form of sweets to less than 10% of calories.

Sugar is an “empty calorie” food. Evidence on sugar

– Causes dental decay & gum disease

– Low nutrient content– Promotes and maintains

obesity

D. Keeping Sweetness in the Diet

Read food labels for clues on sugar content

Use less added sugar Limit soda, surgary

cereals, candy Choose fresh fruits or

those canned in water or juice

III. Complex Carbohydrates

Long chains of sugars (glucoses) arranged as starch or fiber

Also called polysaccharidesTwo types

– Starch– Fiber

A. Starch A plant

polysaccharide composed of hundreds of glucose molecules, digestible by human beings

The storage form of glucose in plants

Found in grains, vegetables, legumes

B. Adding Whole Foods to the Diet

A whole food is one that is altered as little as possible from the plant or animal tissue from which it was taken.

Whole foods have a nutritional advantage over their empty-calorie processed forms.

Parts of a Wheat Kernel

Germ: the nutrient-rich and fat-dense inner part of a whole grain

Endosperm: the bulk of the edible part of a grain; contains starch & protein

Bran: the fibrous protective covering of a whole grain & the chief source of fiber

Husk: the outer, inedible covering of a grain

C. The Bread Box Terms:

– Refined: the process by which the coarse parts of food products are removed

– Enriched: the process by which the B vitamins thiamin, riboflavin, niacin, folic acid & the mineral iron are added to refined grains & grain products at levels specified by law

Cont’d

– Fortified Foods: foods to which nutrients have been addedCommonly eaten foods are fortified

with nutrients such as iodine, vitamin D or calcium to help prevent a nutrient deficiency or to reduce the risk of chronic disease

– Whole grains: a grain that is not refined

D. Fiber

The indigestible residues of food, composed mostly of polysaccharides

Yields few calories, if any Helps support plant structure Two types:

– Insoluble– Soluble

Cont’d

Insoluble fiber– Does not dissolve in water– Cellulose, hemicellulose & lignin

Soluble fiber– Either dissolves or swells in water– Pectin, gums, mucilages & some

hemicelluloses

E. Health Effects of Fiber Fiber in the diet is associated with several

diseases– Digestive tract: Maintain health & function– Cardiac: Helps control blood cholesterol– Diabetes: Moderates blood glucose levels– Cancer: Hinders action of cancer-causing

agents– Obesity: May help prevent obesity

Different forms of fiber have different health effects

Cont’d TOO MUCH FIBER?

– No RDA; recommended is 20-35 grams per day

– Too much fiber can:Cause dehydrationCarry minerals out of the bodyCause nutrient and energy deficiencies

from eating too much bulk in the malnourished, elderly and children

F. Adding Fiber to Your Diet

Foods that are high in fiber include:– Plant foods

(especially those with skins & seeds)

– Whole grains– Fruits– Vegetables

IV. How the Body Handles Carbohydrates

A. Maintaining blood glucose levels

B. Hypoglycemia

C. Hyperglycemia (Diabetes)

V. Alternatives to Sugar

Minimal or no calories Many times sweeter than sugar Current products:

– Saccharin– Aspartame– Sucralose– Acesulfame