The Carbohydrates: Sugars, Starch, & Fibers

1. The Carbohydrates:Sugars, Starch, & Fibers H H-C-O-H C O H H H C O-H C H-O O-H H C C The Structure of Glucose H O-H

2. Carbohydrates • Compounds composed of carbon, oxygen, and hydrogen arranged as monosaccharides or multiples of monosaccharides. Most, but not all, have a ratio of one carbon molecule to one water molecule: CH2O. • Carbo = carbon (C) • Hydrate = with water (H2O)

3. Simple Versus Complex • Simple- monosaccharides and disaccharides, the sugars. • Complex- polysaccharides composed of straight or branched chain monosaccharides, starches and fibers. • Mono = one • Di = two • Poly = many

4. Simple Carbohydrates- Monosaccharides • All have the same numbers and kinds of atoms, but in different arrangements which accounts for their differing sweetness. • Glucose, also known as dextrose. • Fructose, the sweetest of the monosaccharides, found abundantly in fruits and honey. • Galactose

5. Simple Carbohydrate- Disaccharides • The disaccharides are pairs of the monosaccharides. Glucose appears in all three. • Maltose = glucose + glucose • Sucrose = glucose + fructose, table sugar. • Lactose = glucose + galactose, milk sugar.

6. Complex Carbohydrates • Glycogen • Starches • Fibers

7. Glycogen • Glycogen- an animal polysaccharide composed of glucose. It is manufactured and stored in the liver and muscles as a storage form of glucose. Its branched chain structure of glucose molecules allows for rapid hydrolysis into glucose for energy.

8. Starches • Starches- plant polysaccharides composed of glucose.

9. Fibers • Fibers- in plant foods, the nonstarch polysaccharides that are not digested by human digestive enzymes, although some are digested by GI tract bacteria. Fibers include cellulose, hemicelluloses, pectins, gums, and mucilages as well as the nonpolysaccharides lignins, cutins, and tannins.

10. Major Food Source Fruits (apples, citrus) oats barley legumes Action In Body Delays GI transit Delays glucose absorption Lowers cholesterol Soluble Fiber

11. Major Food Source Wheat bran Corn bran Whole grain breads Cereals Vegetables Action In Body Accelerate GI transit Increase fecal weight Promotes BM Insoluble Fiber

12. Classifications of Fibers • Cellulose- the primary constituent of plant cell walls. Composed of glucose molecules connected in long unbranched chains. The bonds are resistant to digestion of human enzymes. • Hemicelluloses- the main constituent of cereal fibers. They are composed of monosaccharide backbones with branching side chains. Some are soluble while others are not.

13. Classifications Of Fibers {continued} • Pectins- consist of a backbone derived from carbohydrate with side chains of various monosaccharides. These are found in fruits and vegetables. Commonly used by the food industry to thicken jellies or to keep salad dressings from separating. • Gums and Mucilages- composed of various monosaccarides and their derivatives. Commonly used by the food industry as stabilizers.

14. Classifications Of Fibers {Continued} • Lignin- is a nonpolysaccharide fiber with a three dimensional structure. This structure provides strength and rigidity. Few foods people eat contain lignin. It is found in the woody parts of vegetables and the small seeds of fruits like strawberries.

15. Classifications Of Fibers {Continued} Other classifications of fibers- • Water-holding capacity • Viscosity • Cation-exchange capacity • Bile-binding capacity • Fermentability

16. Digestion And Absorption Of Carbohydrates • In the mouth- chewing stimulates the flow of saliva. Salivary amylase starts to work by hydrolyzing the long chains into shorter ones. • In the stomach- there are no enzymes produced by the stomach which digest starch. Fiber delays gastric emptying. • In the small intestines- most of the work is done here. Pancreatic amylase enters the intestine via the pancreatic duct. Specific enzymes dismantle each of the dissacharides.

17. Digestion And Absorption Of Carbohydrates {Continued} • In the large intestines- insoluble fiber attracts water which softens the stool for passage. Bacteria also ferment fiber which generates gas. • Absorption into the bloodstream- mono- saccharides, the end products of carbohydrate digestion, enter the capillaries of the intestinal villi. From there they travel to the liver via the portal vein.

18. Glucose In The Body • The primary role of carbohydrates in the body is to supply the body’s cells with glucose for energy. • Storing glucose as glycogen • Making glucose from protein • Making ketone bodies from fat fragments • Converting glucose to fat

19. Regulating Blood Glucose Glucose homeostasis- the body must maintain blood glucose within normal limits to nourish the cells. The regulating hormones- • Insulin- secreted by special cells of the pancreas in response to increased blood glucose concentrations to control the transport of glucose from the blood to the cells. • Glucagon- secreted by special cells of the pancreas in response to low blood glucose concentrations, it elicits the release of glucose from storage.

20. Regulating Blood Glucose {Continued} • Epinephrine (adrenaline)- “fight-or-flight”. When a person experiences stress, this hormone acts quickly, ensuring that the body cells will have fuel in emergency situations by mobilizing glucose from the liver.

21. Falling Outside The Normal Range • Diabetes- a disorder of carbohydrate metabolism resulting from inadequate or ineffective insulin. • Hypoglycemia- an abnormally low blood glucose concentration. • High blood sugar may result in confusion and difficulty breathing, if left untreated could be fatal. • Low blood sugar could result in dizziness and weakness, if left untreated could be fatal.

22. Health Effects Of Sugar • Estimated that on the average each person consumes ~45 pounds of sugar per year. • Can contribute to nutrient deficiencies by supplying energy without supplying nutrients. “Empty calories” • Can contribute to tooth decay.

23. Recommended Intakes Of Sugars • Dietary guidelines for Americans urge only moderate consumption of sugars. • Recommendations specify that sugar should only account for 10% or less of the day’s total energy intake.

24. Health Effects Of Starches And Fibers • Foods rich in complex carbohydrates tend to be low in fat. • Foods rich in soluble fibers lower blood cholesterol, reducing the risk of heart disease. • Diets high in fruits and vegetables, especially citrus fruits and green and yellow vegetables, help prevent certain types of cancers from forming. • Dietary fibers enhance intestinal health.

25. Recommended Intakes Of Starches And Fibers • Dietary recommendations suggest that carbohydrates provide 55-60% of energy requirements. • The American Dietetic Association suggests 20-35 grams of fiber daily.