Carbohydrates: the Main Energy Source

CHAPTER 4 CARBOHYDRATES: THE MAIN ENERGY SOURCE

Student Performance Objectives After reading this chapter and participating in class presentations and discussions, each student shall be able to:

1. Define the thirty-five key terms. 2. Recite the food exchanges that are the primary contributors of carbohydrate to the diet. 3. List the two forms of dietary fiber. 4. Recognize the recommended dietary goal for carbohydrate content of one's diet and the limitations recommended for the amount of refined sugar consumed. 5. Identify the monosaccharide that is of most importance to human metabolism. 6. Outline the four major fates of blood glucose. 7. List the three body energy sources of carbohydrate and estimate the amount of each stored in the body. 8. Identify the site of gluconeogenesis. 9. Name an amino acid that can be converted to glucose and the metabolic by-product of fat that can be converted to glucose. 10. Recite the amount of ATP produced via anaerobic metabolism and the amount produced via aerobic metabolism. 11. Outline the increase in reliance on carbohydrate as an energy source as exercise intensity increases from rest to maximal exercise, and as exercise time increases. 12. Justify, using two reasons, that carbohydrate is the most important energy food for exercise. 13. Outline the four significant changes that occur in the body as a result of several months of an endurance exercise program. 14. Summarize the hormonal mechanism that helps maintain and even increase blood glucose levels during exercise. 15. Identify the factors that limit performance in intermittent, anaerobic-type exercise and prolonged endurance exercise. 16. Recognize the generalizations, based on research into supplementation with glucose or other forms of carbohydrates, of the effect of carbohydrate supplementation on delaying the onset of fatigue and improving performance. 17. Describe the type of event or activity that may benefit from carbohydrate feedings. 18. Recognize the recommendations for the timing of feedings and the type, amount, and concentration of carbohydrate to prevent fatigue during prolonged exercise. 19. Identify the major limitation to glucose ingestion as a means to delay the onset of fatigue. 20. Develop an effective protocol for carbohydrate supplementation before and during exercise. 21. Outline an effective protocol for carbohydrate loading. 22. List the potential detrimental effects of carbohydrate loading. 23. Justify the need for eating foods rich in dietary fiber. 24. Differentiate between the carbohydrate substances that have a potential for ergogenic effects and those that show no benefit. 25. Defend the recommendation that refined sugar should amount to less than 10 percent of the daily caloric intake. 26. Justify the benefit of complex carbohydrates to one's health. 27. List the alternate sources of calcium that the lactose-intolerant individual can use to insure adequate calcium intake. 28. Outline the negative effects of alcohol, ranging from one drink a day to heavy consumption. Key Terms Alcoholism: A rather undefined term used to describe individuals who abuse the effect of alcohol; an addiction or habituation that may result in physical and/or psychological withdrawal effects.

Blood alcohol content (BAC): The concentration of alcohol in the blood, usually expressed as milligram percent.

Carbohydrate loading: A dietary method used by endurance-type athletes to help increase the carbohydrate (glycogen) levels in their muscles and liver.

Carbohydrates: A group of compounds containing carbon, hydrogen, and oxygen. Glucose, glycogen, sugar, starches, fiber, cellulose, and the various saccharides are all carbohydrates.

Cirrhosis: A degenerative disease of the liver, one cause being excessive consumption of alcohol.

Complex carbohydrates: A term used to describe foods high in starch, such as bread, cereals, fruits, and vegetables as contrasted to simple carbohydrates such as table sugar.

Cori cycle: Cycle involving muscle breakdown of glucose to lactate, lactate transport via blood to the liver for reconversion to glucose, and glucose returning to the muscle.

Cortisol: A hormone secreted by the adrenal cortex with glucogenic potential, helping to convert amino acids to glucose. Dietary fiber: Fiber in plant foods that cannot be hydrolyzed by the digestive enzymes.

Disaccharide: Any one of a class of sugars that yield two monosaccharides on hydrolysis; sucrose is the most common.

Epinephrine: A hormone secreted by the adrenal medulla that stimulates numerous body processes to enhance energy production, particularly during intense exercise.

Ergolytic: An agent or substance that may lead to decreases in work productivity or physical performance.

Ethanol: A colorless liquid with depressant effects; ethyl alcohol or ethanol is the alcohol designed for human consumption.

Fetal alcohol effects (FAE): Symptoms noted in children born to women who consumed alcohol during pregnancy. Not as severe as the fetal alcohol syndrome.

Fetal alcohol syndrome (FAS): The cluster of physical and mental symptoms seen in the child of a mother who consumes excessive alcohol during pregnancy.

Fructose: A monosaccharide known as levulose or fruit sugar; found in all sweet fruits.

Galactose: A monosaccharide formed when lactose is hydrolyzed into glucose and galactose.

Glucagon: A hormone secreted by the pancreas; basically it exerts actions just the opposite of insulin, i.e., it responds to hypoglycemia and helps to increase blood sugar levels.

Gluconeogenesis: The formation of carbohydrates from molecules that are not themselves carbohydrate, such as amino acids and the glycerol from fat.

Glucose: A monosaccharide; a thick, sweet, syrupy liquid.

Glucose-alanine cycle: The cycle in which alanine is released from the muscle and is converted to glucose in the liver.

Glucose polymer: A combination of several glucose molecules into a more complex carbohydrate.

Glycemic index: An index expressing the effects of various foods on the rate and amount of increase in blood glucose levels.

Hyperglycemia: Elevated blood-glucose levels.

Hypoglycemia: A low blood-sugar level.

Insoluble dietary fibers: Dietary fiber that is not soluble in water, such as cellulose.

Insulin: A hormone secreted by the pancreas involved in carbohydrate metabolism.

Lactose intolerance: Gastrointestinal disturbances due to an intolerance to lactose in milk; caused by deficiency of lactose, an enzyme that digests lactose. Millimole: One thousandth of a mole.

Monosaccharides: Simple sugars (glucose, fructose, and galactose) that cannot be broken down by hydrolysis.

Polysaccharide: A carbohydrate that upon hydrolysis will yield more than ten monosaccharides.

Proof: Relative to alcohol content, proof is twice the percentage of alcohol in a solution; 80- proof whiskey is 40 percent alcohol.

Reactive hypoglycemia: A decrease in blood glucose caused by an excessive insulin response to hyperglycemia associated with a substantial intake of high-glycemic-index foods.

Simple carbohydrates: Usually used to refer to table sugar, or sucrose, a disaccharide; may refer also to other disaccharides and the monosaccharides.

Soluble dietary fibers: Dietary fibers in plants such as gums and pectins that are soluble in water.