Chapter 4. The Carbohydrates: Sugar, Starch, and Fiber. The Body’s Need for Carbohydrates. The primary role of carbohydrates is to provide the body with energy (calories). Carbohydrates are the preferred fuel for the brain and nervous system.
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The Carbohydrates: Sugar, Starch, and Fiber
The primary role of carbohydrates is to provide the body with energy (calories).
Carbohydrates are the preferred fuel for the brain and nervous system.
Carbohydrates are the ideal fuel compared to other alternatives:
Less expensive than protein.
High-fat diets are associated with chronic disease.
Carbohydrates: compounds made of single sugars or multiples of them and composed of carbon, hydrogen, and oxygen atoms.
carbo = carbon (C)
hydrate = water (H2O)
Complex carbohydrates: long chains of sugars (glucose) arranged as starch or fiber. Also called polysaccharides.
poly = many
saccharides = sugar unit
Simple carbohydrates (sugars): the single sugars (monosaccharides) and the pairs of sugars (disaccharides) linked together.
Carbohydrate-rich foods are obtained almost exclusively from plants.
Milk is the only animal-derived food that contains significant carbohydrate.
All carbohydrates are composed of single sugars, alone or in various combinations.
Single Sugars - Monosaccharides:
Glucose: (GLOO-koce) the building block of carbohydrate; a single sugar used in both plant and animal tissues as quick energy. A single sugar is known as a monosaccharide.
mono = one
Fructose: (FROOK-toce) fruit sugar—the sweetest of the single sugars.
Galactose: (ga-LACK-toce) another single sugar that occurs bonded to glucose in the sugar of milk.
Double Sugars - Disaccharides:
Sucrose: (SOO-crose) a double sugar composed of glucose and fructose. A double sugar is known as a disaccharide.
di = two
Maltose: a double sugar composed of two glucose units.
Lactose: a double sugar composed of glucose and galactose; commonly known as milk sugar.
Sugar cane and sugar beets are purified to make sucrose.
Food examples include white (table) sugar, brown sugar, powdered sugar.
Sucrose is common in sweets.
A sampling of foods providing added sugars to the diet.
Enzymes: protein catalysts. A catalyst facilitates a chemical reaction without itself being altered in the process.
(Proteins are discussed in Chapter 6.)
Lactose intolerance: inability to digest lactose as a result of a lack of the necessary enzyme lactase.
Symptoms include nausea, abdominal pain, diarrhea, or excessive gas that occurs anywhere from 15 minutes to a couple of hours after consuming milk or milk products.
Complex carbohydrates include starch and fiber.All starchy foods are plant foods.
Sources of starch include:
Refined:refers to the process by which the coarse parts of food products are removed.
Enriched: refers to a process by which the B vitamins thiamin, riboflavin, niacin, folic acid, and the mineral iron are added to refined grains and grain products at levels specified by law.
Fortified foods: foods to which nutrients have been added. Typically, commonly eaten foods are chosen for fortification with added nutrients to help prevent a deficiency of a nutrient (iodized salt, milk with vitamin D) or to reduce the risk of chronic disease (juices with added calcium).
Fiber: the indigestible residues of food, composed mostly of polysaccharides. The best known fibers are cellulose, hemicellulose, pectin, and gums.
Comes from the supporting structures of plants: leaves, stems and seeds.
Cannot be broken down by human digestive enzymes although some may be broken down by bacteria residing in the digestive tract.
Fiber has few if any calories because it is not digested.
Insoluble fiber includes the fiber types called cellulose, hemicellulose, and lignin.
Insoluble fibers do not dissolve in water.
Soluble fiber includes the fiber types called pectin, gums, mucilages, some hemicelluloses, and algal substances (for example, carageenan).
Soluble fibers either dissolve or swell when placed in water.
Foods rich in insoluble fiber:
Foods rich in soluble fiber:
Diverticulosis: The outpocketings of intestinal linings that balloon through the weakened intestinal wall muscles are known as diverticula.
Added Sugars: Use Discretion
Choose and prepare foods with little added sugar (Dietary Guidelines).
Added Sugar:sugars and other caloric sweeteners that are added to foods during processing or preparation. Added sugars do not include naturally occurring sugars that are found in milk and fruit.
Choose most often the naturally occurring sugars (DRI).
For those who meet their nutrient needs, maintain a “healthy body weight” and still need additional calories--maximum intake = 25% or less for added sugars (DRI).
Breakfast: Try a higher-fiber grain: oatmeal, whole-grain muffin, or whole-grain cereal
Whole grains are low in fat and added sugars
Baking recipes: Substitute whole-grain flour for 1/4 of all-purpose flour
Make a fiber-rich snack mix from whole grain cereals, popcorn, and nuts
Try whole-wheat pasta, rice, and breads
Combine whole grains in mixed dishes
If the blood delivers more glucose than the cells need, glycogen will be built.
Glycogen (GLY-co-gen): a polysaccharide composed of chains of glucose, manufactured in the body and stored in liver and muscle.
As a storage form of glucose, liver glycogen can be broken down by the liver to maintain a constant blood glucose level when carbohydrate intake is inadequate.
is broken down in the body to:
A. When a person overeats (feasting):
and then stored as:
Body fat stores
B. When a person draws on stores (fasting):
and then used for:
is broken down in the body to:
Fig. 4-4, p. 119
When a person eats, blood glucose rises. High blood glucose stimulates the pancreas to release insulin. Insulin serves as a key for entrance of blood glucose into cells. Liver and muscle cells store the glucose as glycogen. Excess glucose can also be stored as fat.
Later, when blood glucose is low, the pancreas releases glucagon, which serves as the key for the liver to break down stored glycogen into glucose and release it into the blood to raise blood glucose levels.
Insulin: a hormone secreted by the pancreas in response to high blood glucose levels; it assists cells in drawing glucose from the blood.
Glucagon (glue-cuh-gon): a hormone released by the pancreas that signals the liver to release glucose into the bloodstream.
Glycemic index (GI): a scale that ranks carbohydrate-containing foods by how much they raise blood glucose levels compared to a standard food such as glucose or white bread. The glycemic load (GL) is a measure of the extent to which blood glucose is raised by a given amount of carbohydrate-containing food.
Glycemic effect: the effect of food on a person’s blood glucose and insulin response – how fast and high the blood glucose rises and how quickly the body responds by normalizing.
High glycemic index foods:
French, white, other soft breads/bagels
Certain cereals (Cheerios, Corn Flakes, Rice Krispies)
Honey, regular soft drinks, jelly beans
Intermediate glycemic index foods:
Cream of Wheat, instant oatmeal, Shredded Wheat
Sourdough & rye breads
Banana, pineapple, orange juice
Low glycemic index foods:
Whole-grain, heavy breads
Bran cereals, toasted Muesli cereal, whole oats
Apples, oranges, peaches
Baked beans, lentils, other legumes
Hypoglycemia (HIGH-po-gligh-SEEM-eeuh): an abnormally low blood glucose concentration—below 60 to 70 mg/100 mL.
Ketosis: abnormal amounts of ketone bodies in the blood and urine; ketone bodies are produced from the incomplete breakdown of fat when glucose is unavailable for the brain and nerve cells.
Hyperglycemia: an abnormally high blood glucose concentration, often a symptom of diabetes.
Diabetes (dye-uh-BEET-eez): a disorder (technically termed diabetes mellitus) characterized by insufficiency or relative ineffectiveness of insulin, which renders a person unable to regulate the blood glucose level normally.
Type 1 diabetes
Type 2 diabetes
Gestational diabetes (see Chapter 11)
Research studies have not shown a direct link between sugar and obesity, diabetes, heart disease, hyperactivity in children or criminal behavior.
Empty-calorie foods: a phrase used to indicate that a food supplies calories but negligible nutrients.