Chapter 4 - Carbohydrates: Sugars, Starches, and Fiber

Carbohydrates in Modern Diet

• Basis of most modern diets

  • provide >1/2 of kcals consumed by American

• Provide a readily available source of energy

  • 4 kcal per gram

• Provide a wide variety of nutrients needed for health when consumed in “whole food” form

Sources of carbohydrates

yogurt, orange, banana, corn, potato, whole-meat bread, spaghetti

Bran layers

component of whole grain (unrefined) products that contain most of the fiber and are a good source of many vitamins and minerals

Endosperm

component of whole grain (unrefined) products that is the largest part of the kernel and made primarily of starch

Germ

component of whole grain (unrefined) products that is the embryo where sprouting occurs and is a good source of oil and is rich in vitamin E

Refining grains

separates carbohydrates from many essential nutrients found in whole unrefined goods

What are refined grains enriched with?

thiamin, riboflavin, niacin, and iron; fortified with folate

What do refined grains not contain?

magnesium, vitamin E, and some of B vitamins or other nutrients of whole grain

Simple carbohydrates

monosaccharide, disaccharide

Complex carbohydrates

polysaccharide

Monosaccharide

• a single sugar unit

• the three most common in the diet are glucose, fructose, and galactose

Glucose

monosaccharide that circulates the blood; the most important carbohydrate fuel for the body

Fructose

monosaccharide found in fruits, vegetables, honey, and high-fructose corn syrup

Galactose

monosaccharide that is part of milk sugar

Photosynthesis

plants convert glucose to starch; when a human eats plants, digestion converts the starch back to glucose

Disaccharides

• made of two monosaccharides linked together

• maltose, sucrose, and lactose

Sucrose (table sugar)

a disaccharide formed by linking glucose with fructose; the only sweetener in the U.S. that can be labeled “sugar”

Maltose

a disaccharide that is formed in the digestive tract when starch is digested

Lactose

a disaccharide made of glucose linked to galactose; often found in milk, ice cream, and other diary products

Making and breaking sugar chains

• hydrolysis reaction - breaks sugar molecules apart

• dehydration reaction - links two sugar molecules together

Complex carbohydrates

oligosaccharides, polysaccharides

Oligosaccharides

short chains containing 3-10 monosaccharides

Polysaccharides

• long chains of monosaccharides

• include glycogen found in animals

• include starch and fiber found in plants

Dietary fiber

can’t be digested or absorbed by humans, but is an important part of the digestive process and health of the GI tract

Two types of fiber

• soluble - dissolves in water

• insoluble - doesn’t dissolve in water

Sources of soluble fiber

legumes, prunes, apricots, raisins, oranges, bananas, oats, flaxseed

Sources of insoluble fiber

wheat bran, whole-meat bread, broccoli, corn, eggplant, nuts and seeds

Lactose intolerance

• occurs when there is not enough enzyme lactase in the small intestine to digest the milk sugar lactose

• undigested lactose cannot be absorbed and passes into the large intestine

• lactose is rapidly metabolized by intestinal bacteria, producing acids and gas

• symptoms can include abdominal distention, flatulence, cramping and diarrhea

What does the the presence of fiber affect?

GI functions, intestinal microbiota, amount of intestinal gas, nutrient absorption

How does fiber affect the GI function?

• increases the weight of material in the lumen of the intestine producing a larger, softer stool, which promotes healthy bowel function

• prevents constipation

• reduces transit time

Delivering glucose to the body

the concentration of glucose in the blood is regulated by the liver and by enzymes secreted from the pancreas

• glycemic response, glycemic index, glycemic load

Glycemic response

how quickly and how high blood glucose rises after carbohydrates are consumed

Glycemic index

a ranking of how a food affects the glycemic response

Glycemic load

calculated by multiplying a food’s glycemic index by the amount of available carbohydrate in a a serving of the food

Type 1 diabetes

insulin is no longer made in the body

Type 2 diabetes

insulin is present, but the cells do not respond (insulin resistance)

Gestational diabetes

occurs during pregnancy

How glucose provided energy

• glucose is metabolized through cellular respiration (aerobic metabolism) to produce ATP, a form of energy

• uses 6 molecules of oxygen to convert 1 molecule of glucose into 6 molecules of carbon dioxide, 6 molecules of water, and 38 molecules of ATP

Reactive hypoglycemia

over secretion of insulin in response to carbohydrate intake; treatment include frequent small meals high in protein

Fasting hypoglycemia

abnormal insulin secretion not related to food intake

Low carbohydrate diets

• cause less insulin to be released

• produces more ketones

Carbohydrates and heart disease

• diets high in whole grain reduce the risk

• water-soluble fiber binds dietary cholesterol and reduces absorption

Colon cancer and fiber intake

lower in populations that consume diets high in fiber