This Document Contains Chapters 3 to 4 Chapter 3: Energy Systems and Exercise Overarching Concepts 1. The body has three primary energy systems to re-phosphorylate ADP to form ATP. 2. These three energy systems work in concert although one energy system usually predominates. 3. Each energy system has distinct advantages (e.g. speed, amount produced, duration) and limitations (e.g. speed, amount produced, duration, depletion of substrate, undesirable effects). 4. Carbohydrates and fats (and to a small degree proteins) found in food are biochemically converted and available for use as immediate or stored (future) energy. 5. The percentage of energy derived from carbohydrates and fats can be estimated by measuring respiratory exchange ratio (RMR). Learning Objectives LO 3.1 Describe the rephosphorylation of ATP and the general characteristics of the creatine phosphate, anaerobic glycolysis, and oxidative phosphorylation energy systems. LO 3.2 Describe the specific characteristics of the creatine phosphate energy system, and explain how it is used to replace ATP during exercise. LO 3.3 Describe the specific characteristics of the anaerobic glycolysis energy system, and explain how it is used to replace ATP during exercise. LO 3.4 Describe the specific characteristics of the oxidative phosphorylation (aerobic) energy system and explain how it is used to replace ATP during exercise. LO 3.5 Explain the process of aerobic metabolism of carbohydrates, fats, and proteins (amino acids), and the concept of measuring fuel utilization with the respiratory exchange ratio, and describe the factors that influence fuel utilization. LO 3.6 Describe the response of oxygen consumption to steady state and submaximal exercise, and explain the concept of maximal oxygen consumption (V ˙ O2max). Chapter Outline I. 3.1 Overview of energy systems • ATP is hydrolyzed, or split, to release energy for exercise, leaving adenosine diphosphate (ADP). • ATP is split at a fast rate during exercise. • ADP is rephosphorylated to re-form ATP in an endergonic, or energy-requiring reaction. • The three major energy systems—creatine phosphate, anaerobic glycolysis, and oxidative phosphorylation—are used to replenish ATP. • All three energy systems are active at all times; however, one may be the predominant system depending upon the intensity and duration of the exercise activity. A. ADP is rephosphorylized to form ATP. 1. Hydrolysis of ATP 2. Rephosphorylation of ADP to form ATP 3. Use of ATP for energy by exercising skeletal muscle 4. Characteristics of the three major energy systems to replenish ATP a. Creatine phosphate 1. Very fast, very short duration, very small amount b. Anaerobic glycolysis 1. Fast, short duration, small amount c. Oxidative phosphorylation 1. Very slow, very long duration, large amount 5. Interaction of the three energy systems Question for discussion: What energy system is likely to be used for exercise that is of short duration but very high intensity? II. 3.2 The creatine phosphate energy system • Creatine phosphate is a high-energy phosphate that is stored in muscle and can be used to replenish ATP very quickly. • Creatine is synthesized in the body and/or consumed in the diet (meat or fish) or as a supplement. • Creatine phosphate is the preferred energy system during short duration, very high-intensity exercise, and its depletion is associated with muscle fatigue. • Creatine is rephosphorylated to creatine phosphate using the aerobic energy system. A. Creatine phosphate 1. Readily available reservoir of phosphate in muscle to replenish ATP 2. A variety of terms and abbreviations may be used interchangeably a. Creatine phosphate or phosphocreatine b. CrP, CP, PC, PCr B. Creatine is consumed in the diet or synthesized in the body from amino acids. 1. Amine (nitrogen containing compound) 2. Sources: diet (beef or fish), supplementation, or produced by the body 3. Stored in muscle as creatine (1/3) and creatine phosphate (2/3) 4. Excretion is approximately 2 g/day, equal to the amount synthesized and/or obtained from food 5. Vegetarians may have less in muscle than meat and fish eaters C. The creatine phosphate (CrP) energy system rephosphorylates ADP to ATP rapidly. 1. Very rapid one-step chemical reaction 2. Catalyzed by creatine kinase (CK) 3. Anaerobic 4. 1:1 (CrP:ATP) 5. 5- to 10-second duration 6. Fatigue associated with near depletion of creatine phosphate 7. Predominant energy system for very high-intensity exercise a. Sprints b. Powerful bursts of activity c. High force production 8. Primary advantage: speed; primary disadvantage: depletion of substrate 9. Focus on research: Determining the Use of ATP and Creatine Phosphate in Skeletal Muscle during Exercise D. Rephosphorylation of creatine to creatine phosphate depends upon aerobic metabolism. 1. Creatine shuttle 2. Requires oxygen 3. Takes place in mitochondria 4. Can take 1-2 minutes after very high-intensity exercise to restore creatine phosphate E. Spotlight on supplements: Creatine loading and supplementation 1. CrP concentration can be increased up to approximately 20% with supplementation 2. Some people are nonresponders to supplementation if CrP concentrations are already near maximum 3. Usual dose 3-5 g/day 4. Loading dose of 20-25 g/day in 4-5 doses for 5-7 days; not necessary unless time is urgent 5. No immediate increase in strength, speed, or power 6. No direct effect on performance except for in power lifters 7. Indirect effect by allowing increased training that improves strength, speed, or power 8. Increases intracellular water in muscle cells 9. Safe with some minor side effects 10. Effective for strength and power athletes Question for discussion: What are the major advantages and disadvantages of the creatine phosphate energy system? III. 3.3 The anaerobic glycolysis energy system • Glycolysis is a series of chemical steps, beginning with glucose or glycogen that result in the formation of ATP. • Glycolysis replenishes ATP quickly, although not as quickly as the creatine phosphate energy system. • Glycolysis is the predominant energy system used for high-intensity or repeated exercise bouts and results in the formation of lactate. • Lactate produced in exercising muscle can be metabolized aerobically by a variety of tissues. A. Anaerobic glycolysis 1. The conversion of glucose to lactate in muscle under anaerobic conditions 2. Substrate is carbohydrate (glucose) 3. Glycogenolysis is the metabolic breakdown of glycogen to glucose B. Glycolysis uses the energy contained in glucose to rephosphorylate ADP to ATP. 1. 18 chemical steps/reactions, six are repeated 2. 12 chemical compounds/11 enzymes 3. Rate-limiting enzyme is phosphofructokinase (PFK) 4. Anaerobic 5. 2 ATP produced if starting point is glucose; 3 ATP if glycogen 6. Fast but not as fast as creatine phosphate 7. 1-2 minute duration 8. Fatigue associated with decreased pH (metabolic acidosis) 9. Predominant energy system for high-intensity exercise a. Long sprints b. Repeated sprints (“stop and go”) or intervals c. Repeated high-force production activities (weight lifting repetitions) 10. Primary advantage: speed, substrate (carbohydrate) availability, useful by-product (lactate) 11. Primary disadvantage: fatigue associated with a decline in pH C. Lactate is metabolized aerobically. 1. Converted to pyruvate and metabolized aerobically 2. In the liver, converted to glucose via the Cori cycle D. Spotlight on... Lactate Threshold (LT) 1. Point of sudden increase in blood lactate concentration 2. Erroneously called Anaerobic Threshold (AT) 3. Lactate production outpaces lactate removal mechanisms 4. LT associated with an exercise intensity that can be sustained for long periods during endurance exercise Question for discussion: If exercise intensity is increased gradually, why does the concentration of lactate in the blood not increase until after approximately 50–60 percent of maximal oxygen consumption? IV. 3.4 The oxidative phosphorylation energy system • Oxidative phosphorylation (aerobic metabolism) produces ATP relatively slowly but in large amounts. • Carbohydrates, fats, and proteins can be metabolized via the oxidative phosphorylation energy system, although protein is not a preferred source, particularly for exercise. • Oxidative phosphorylation is the predominant energy system used at rest and for low- to moderate-intensity activities and is the predominant energy system for endurance exercise. • Oxidative phosphorylation is referred to as the aerobic energy system because oxygen is used as the final electron acceptor. • Carbohydrates are metabolized in oxidative phosphorylation as glucose or from the storage form, glycogen. • Fats, in the form of fatty acid chains, are prepared for oxidative phosphorylation by a series of chemical steps called beta-oxidation. • The utilization of carbohydrates, fats, and protein depends on the fed-fast cycle. • The fed state favors nutrient storage due to the powerful influence of insulin. • When not in a fed state, other hormones influence the body to release nutrient stores. • Total energy intake influences the use of carbohydrates, fats, and proteins (amino acids) for fuel. • The utilization of carbohydrate, fat, and protein as fuel is complex and depends upon a variety of factors such as diet composition, activity level, health and/or disease state, hormonal status, and time since the last meal. A. Oxidative phosphorylation 1. Requires oxygen (“aerobic metabolism”) 2. Can use carbohydrates, fats, and proteins as substrates 3. Occurs in mitochondria 4. Three phases a. Preparation of substrates for aerobic metabolism (e.g., glycolysis) b. Removal of electrons c. Shuttle of electrons to produce ATP 5. Characteristics a. 124 chemical steps/reactions b. 30 chemical compounds/27 enzymes c. Rate-limiting enzymes are phosphofructokinase (PFK), isocitrate dehydrogenase (IDH), and cytochrome oxidase (CO) d. Aerobic (oxygen must be transported from lungs) e. In skeletal muscle, 36 ATP via glucose; 37 ATP via glycogen f. Slow g. Virtually limitless duration h. Fatigue associated with substrate depletion (e.g., glycogen depletion) i. Predominant energy system for endurance exercise j. Primary advantage: large amount of ATP produced, long duration k. Primary disadvantage: slow ATP production, need for oxygen B. Carbohydrates are oxidized in the Krebs cycle. 1. Takes place in mitochondria 2. Primary function is to remove electrons (oxidation) 3. 10 chemical reactions beginning with acetyl CoA 4. Six oxidation-reduction reactions (coupled) a. Oxidation = removal of electrons b. Reduction = acceptance of electrons c. Common electron accepting compounds 1. NAD (nicotinamide adenine dinucleotide) 2. FAD (flavin adenine dinucleotide) d. NAD and FAD shuttle electrons into the electron transport chain C. Free radicals (reactive oxygen species) 1. Unpaired electrons due to uncoupling of oxidation-reduction reactions 2. Normal part of oxidative phosphorylation 3. If antioxidant systems are overwhelmed, tissue damage may occur (oxidative stress) 4. Excess oxidative stress associated with aging and some chronic diseases D. The electron transport chain uses the potential energy of electron transfer to rephosphorylate ADP to ATP. 1. Takes place in the inner membrane of mitochondria 2. Primary function is to shuttle electrons down the chain 3. ATP and water are produced 4. NAD carriers produce approximately 3 ATP; FAD carriers produce approximately 2 ATP 5. 36 ATP produced in skeletal muscle via glucose; 37 via glycogen 6. 38 ATP produced in other tissues via glucose; 39 via glycogen E. Fats are metabolized aerobically by the oxidation of fatty acids. 1. Most fatty acids used for energy contain 16 or 18 carbons 2. Fats can be mobilized from storage and taken up by tissues 3. To enter the Krebs cycle, fatty acids must go through beta-oxidation a. Occurs in mitochondrial matrix b. 2-carbon segments are removed and converted to acetyl CoA 4. Large amount of ATP produced (e.g., 129 ATP for the fatty acid palmitate) 5. Primary advantage of using fat: large amount of ATP produced, virtually unlimited substrate 6. Primary disadvantage: slow ATP production, need for oxygen F. Proteins are metabolized aerobically by oxidation of amino acids. 1. Least desirable energy source 2. Amino acids enter oxidative phosphorylation at different points a. Pyruvate, acetyl CoA, or other Krebs cycle compounds 3. Minor energy source compared to carbohydrates or fats a. If glycogen depleted, may be 5-10% of total energy production G. The respiratory exchange ratio (RER) indicates utilization of carbohydrate and fat as fuels. 1. Carbohydrates and fats are preferred energy sources 2. Fats are the primary energy source at rest (85%) 3. As exercise intensity increases, % energy from fat decreases 4. 50/50 mix of fats and carbohydrates with modest exercise 5. Carbohydrates are the primary energy source for moderate to hard exercise 6. Proportion of carbohydrates and fats used can be estimated a. Respiratory Exchange Ratio (RER) 1. If only carbohydrate is used, RER = 1.0 2. If only fat is used, RER = 0.70 3. Usually both are fuel sources a. Example: If RER = 0.80, then approximately 32% carbohydrate, approximately 68% fat H. Dietary intake influences carbohydrate, fat, and protein metabolism. I. Metabolism is influenced by the fed-fast cycle. J. The fed state favors nutrient storage. 1. In fed (absorptive) state a. Influence of insulin b. Glucose is used for immediate energy c. Glucose is stored as glycogen for future energy d. Fat is stored for future energy 2. In post-absorptive state a. Influence of hormones other than insulin b. Liver glycogen is broken down to provide glucose to the blood c. Fat is released from storage K. Total energy intake is an important factor. L. Spotlight on... Alcohol (ethanol) metabolism 1. Metabolic priority due to production of toxic intermediary compound 2. Two primary pathways a. Alcohol dehydrogenase (DH), moderate consumption b. Microsomal ethanol-oxidizing system (MEOS), high consumption Question for discussion: If an athlete is exercising and is using the aerobic energy system, how does the body deliver oxygen to the mitochondria in the exercising muscles? V. 3.5 Fuel Consumption • Carbohydrates are metabolized via oxidative phosphorylation as glucose or from the storage form, glycogen. • Fats, in the form of fatty acid chains, are prepared for oxidative phosphorylation by a series of chemical steps called β-oxidation. • The respiratory exchange ratio (RER), the ratio of carbon dioxide produced to oxygen consumed, can be used to determine fuel utilization, or the proportion of energy derived from fat and carbohydrate. • The utilization of carbohydrates, fats, and protein depends on the fed-fast cycle. • The fed state favors nutrient storage due to the powerful influence of insulin. • When not in a fed state, other hormones influence the body to release nutrient stores. • Total energy intake influences the use of carbohydrates, fats, and proteins (amino acids) for fuel. • The utilization of carbohydrate, fat, and protein as fuel is complex due to a variety of factors such as diet composition, activity level, health and/or disease state, hormonal status, and time since the last meal. A. Fats are metabolized aerobically by the oxidation of fatty acids. 1. The principal fats metabolized for energy in the body are fatty acids containing chains of either 16 or 18 carbons (for example, palmitate and stearate, respectively) 2. When fat is needed for energy, triglycerides are broken down and the fatty acid chains are transported to mitochondria for aerobic metabolism 3. Fatty acids must pass through another series of reactions called b- (beta-) oxidation 4. The overall function of β-oxidation is to remove 2-carbon segments from the fatty acid chains and convert them to acetyl CoA 5. Complete metabolism of the fatty acid palmitate results in the production of 113 ATP B. Proteins are metabolized aerobically by the oxidation of amino acids 1. Protein is not “stored” as an energy source in the same sense as are carbohydrates and fats 2. Protein metabolism is complex because there are 20 amino acids and a variety of points of entry into the oxidative process 3. Of the three energy-containing nutrients, protein is the least preferred as a fuel source 4. Not stored for ready access as are carbohydrates and fats 5. Rarely exceeds 10 percent of total energy production C. The respiratory exchange ratio (RER) indicates utilization of carbohydrate and fat as fuels 1. At rest, the preferred fuel source is fat 2. As activity increases, the body begins to rely more on carbohydrates and less on fat as a percentage of total energy expenditure 3. At moderate to hard exercise intensities, nearly all of the energy expenditure is derived from carbohydrates 4. The proportion of energy coming from carbohydrates and fats can be estimated accurately by use of the respiratory exchange ratio (RER), a ratio of the amount of carbon dioxide produced to the amount of oxygen consumed D. Dietary intake influences carbohydrate, fat, and protein metabolism 1. The body has many ways it can adjust its metabolic pathways to meet its short- and long-term energy needs E. Metabolism is influenced by the fed-fast cycle 1. The fed (absorptive) state refers to the 3- to 4-hour period after food is eaten 2. The postabsorptive state is the period of time after the meal is fully absorbed but before the next meal is eaten F. The fed state favors nutrient storage 1. Most important hormone is insulin 2. Energy priority is delivering glucose from carbohydrate-containing foods G. Total energy intake is an important factor. 1. Metabolic adjustments are made when energy intake consistently exceeds or does not meet energy output Questions for discussion: (1) Why is protein not a preferred fuel source compared to fat and carbohydrate? (2) Why is the phrase “you are what you eat” especially true for energy metabolism? VI. 3.6 Oxygen consumption • As exercise intensity increases and the use of oxidative phosphorylation increases to replenish ATP, the amount of oxygen consumed by the body increases. • At the onset of exercise there is often a lag between energy demand and energy provided by oxidative phosphorylation, creating an “oxygen deficit.” • When exercise is stopped, oxygen consumption remains elevated during the recovery period for some time in order to rephosphorylate creatine phosphate used and oxidize lactate produced at the onset of exercise, known as excess postexercise oxygen consumption (EPOC). • Individuals have a maximal ability to consume oxygen, known as maximal oxygen consumption or VO2max. • The respiratory exchange ratio (RER), the ratio of carbon dioxide produced to oxygen consumed, can be used to determine fuel utilization, or the proportion of energy derived from fat and carbohydrate. A. Increased use of aerobic metabolism results in an increase in oxygen consumption. 1. Submaximal exercise a. Oxygen consumption increases at onset of exercise b. Some “lag time” before reaching steady state c. Oxygen deficit d. Post-exercise oxygen consumption (EPOC) B. Each individual has a maximal ability to consume oxygen, or VO2max. 1. Maximum ability to consume oxygen 2. Affected by age, gender, genetics 3. Aerobic exercise training has substantial influence 4. Expressed as ml/kg/min 5. General categories (e.g., health/fitness or well trained) established C. Oxygen consumption is influenced by different skeletal muscle fiber types. Question for discussion: Why is there a lag time in the rise in oxygen consumption at the onset of exercise? VI. Summary and review A. Chapter summary B. Post-test assessment C. Review questions D. References Supplementary Teaching Materials and Classroom Activities Note: The text chapter includes an application exercise comparing utilization of energy systems at different activity intensity levels (p. 85). Activity 3-1 Have students evaluate websites associated with creatine supplementation. This can be an in-class demonstration with websites pre-selected by the instructor or an out-of-class assignment. Student Assignment The purpose of the assignment is to evaluate the content material of a website selling creatine supplements. Using a search engine, enter the words “creatine supplements” into the search box. Choose one commercial site (.com) that sells creatine supplements. Answer the following questions about the website. 1. What is the URL of the website? 2. Describe the product being sold. Who is the target audience? How is the product supposed to work? 3. Describe the objective information found on the site (e.g. ingredients, dose, physiological or biochemical roles, scientific evidence). 4. Describe the subjective information (e.g., advertising, testimonials). 5. Evaluate the objective information (e.g., comparing factual information on the site to information found in the textbook). 6. Describe the subjective information that you think would influence someone to purchase creatine supplements from this website. In your opinion, what is most influential? 7. What information would you like to have seen on the website? 8. Was the following statement clearly visible on the website: “This product is not intended to diagnose, treat, cure or prevent any disease. These statements have not been evaluated by the Food and Drug Administration.” 9. Is the product being sold legal, ethical, safe, and effective? If not, why not? 10. Write a one-paragraph summary of this website. Activity 3-2 Have each student choose a sport that they are familiar with and answer the following questions about energy systems used during training and competition: 1. During competition, which energy system predominates? Give an example of when each of the three energy systems (creatine phosphate, anaerobic glycolysis, oxidative phosphorylation) will be used. 2. During training, which energy system predominates? Give an example of when each of the three energy systems will be used. How do training and competition differ? 3. Using the white board or overhead, categorize the sports based on the predominant energy system used. Have students compare and contrast the sports in each category. This activity may be done individually or in groups. Sharing information about various sports can help students increase knowledge of sports they are unfamiliar with. Activity 3-3 Arrange for students to observe a determination of maximal oxygen consumption and respiratory exchange ratio (RER) in an on-campus exercise physiology laboratory. Arrangements are best made at the beginning of the semester so laboratory personnel have time to prepare. Maximal Oxygen Consumption 1. Express the subject’s maximal oxygen consumption in relative (ml/kg/min) and absolute terms. 2. Comment upon the maximal oxygen consumption of the lab subject(s) compared to the general population (i.e., compared to norms in Appendix H). What percentile group would this subject be in according to his/her gender and age? Fuel Utilization – Respiratory Exchange Ratio Subject will perform submaximal exercise on the treadmill at 3 different intensities. The subject will sit quietly for 3 minutes and then will exercise for 5 minutes at each of the 3 treadmill speeds (2.0 mph, 4.0 mph, and 6.0 mph). Oxygen consumption and carbon dioxide production will be measured at rest and during exercise with a metabolic measurement system. The percentage of energy expenditure from carbohydrates and fats will be determined from the respiratory exchange ratio (RER) – see table in Appendix I. 1. Which fuel source provides the greatest percentage of energy expenditure at rest? 2. What happens to the percentage of energy from the two fuel sources as exercise intensity increases? 3. At what exercise intensity did carbohydrate become the predominant fuel source? Crossword Puzzle Answer Key 1. acetyl CoA 2. lactate 3. glucose 4. beta-oxidation 5. creatine kinase 6. oxaloacetate 7. creatinine 8. pyruvate 9. oxidation 10. amine 11. creatine phosphate 12. glycolysis 13. glycogen Word Find Puzzle Answer Key • 3 major energy systems that replenish ATP: creatine phosphate, anaerobic glycolysis, oxidative phosphorylation • 3 amino acids found in the structure of creatine: arginine, glycine, methionine • 3 things produced when a glucose molecule is split: lactate, hydrogen, energy • 2 molecules that initiate the Krebs cycle: acetyl CoA, oxaloacetate • 3 rate-limiting enzymes: phosphofructokinase, isocitrate dehydrogenase, cytochrome oxidase • 3 states of the body in relation to food intake: fed, postabsorptive, fasting C D R P H O S P H A T E I A Z Y E H C O E W O I T F E E L S T S O N N I G R P H O S P H O F R U C T O K I N A S E H Y T T C R A Z Y H O W C N Y E O N A U D F A S T I N G M A E I K M E E I T E R T B A L L A L L S G T O R R I G I N O H S H T L O V A R E R L G O A V N I G E O Y L Y L D A A H A Y D Y N I E N E A R D A T I Y O C E T A T C A L U O N R P R O X A L O A C E T A T E F F I A E T O O E T T C A N T O M O R R E H S R I G G L Y C O L Y S I S O O W D T E B V E E C S O W O N D R O U B S A E S Y E N I C Y L G E V I T A D I X O M O U T H E R E S L A C E T Y L C O A P H O S P H O R Y L A T I O N E E P I Chapter 3 Crossword Puzzle Across Down 1. A chemical compound that is an important entry point into the Krebs cycle. 3. A sugar found in food and in the blood. 5. Enzyme that catalyzes the creatine phosphate energy system. 7. Waste product excreted in the urine. 9. Chemical process of giving up electrons. 11. Organic compound that stores potential energy in its phosphate bonds. 12. Metabolic breakdown of glucose. 13. Storage form for carbohydrates in the body. 2. The metabolic end product of anaerobic glycolysis. 4. Chemical process of breaking down fatty-acid chains for aerobic metabolism. 6. Chemical compound that is one of the intermediate compounds in the Krebs cycle. 8. Chemical compound that is an important intermediate of glycolysis. 10. An organic compound containing nitrogen, similar to a protein. Chapter 3 Word Find Puzzle C D R P H O S P H A T E I A Z Y E H C O E W O I T F E E L S T S O N N I G R P H O S P H O F R U C T O K I N A S E H Y T T C R A Z Y H O W C N Y E O N A U D F A S T I N G M A E I K M E E I T E R T B A L L A L L S G T O R R I G I N O H S H T L O V A R E R L G O A V N I G E O Y L Y L D A A H A Y D Y N I E N E A R D A T I Y O C E T A T C A L U O N R P R O X A L O A C E T A T E F F I A E T O O E T T C A N T O M O R R E H S R I G G L Y C O L Y S I S O O W D T E B V E E C S O W O N D R O U B S A E S Y E N I C Y L G E V I T A D I X O M O U T H E R E S L A C E T Y L C O A P H O S P H O R Y L A T I O N E E P I Instructions: In the grid above, find the following words or phrases, and then write them beside each clue. (Note: Words that are part of a phrase may be placed separately in the grid.) • 3 major energy systems that replenish ATP: • 3 amino acids found in the structure of creatine: • 3 things produced when a glucose molecule is split: • 2 molecules that initiate the Krebs cycle: • 3 rate-limiting enzymes: • 3 states of the body in relation to food intake: Chapter 4: Carbohydrates Overarching Concepts 1. Carbohydrate consumption is at the heart of sports nutrition recommendations for all athletes in training. 2. The daily resynthesis of muscle glycogen is crucial. 3. Understanding CHO digestion, absorption, and metabolism helps athletes make appropriate choices for the type and amount of CHO needed to support training and performance. 4. In addition to an adequate amount of CHO daily, athletes need to appropriately time their intake of CHO before, during, and after exercise. 5. Most athletes fall short of meeting CHO recommendations. 6. Consuming a carbohydrate-rich diet routinely takes planning and effort. Learning Objectives LO 4.1 Classify carbohydrates according to their chemical composition. LO 4.2 Describe the digestion and absorption of carbohydrates. LO 4.3 Explain the metabolism of glucose. LO 4.4 Describe how muscle glycogen and blood glucose are used to fuel exercise. LO 4.5 Detail and explain carbohydrate recommendations for athletes, including specific guidelines for intake before, during, and after exercise. LO 4.6 Determine the daily carbohydrate needs of an athlete, and select carbohydrate-containing foods to meet the recommended intake. Chapter Outline I. Introduction A. Pre-test assessment B. Introductory concepts 1. Primary energy source for moderate to intense exercise 2. Carbohydrates (CHO) are found in food as sugars, starches, and cellulose 3. Carbohydrates are found in the body as glucose and glycogen 4. CHO stores are depleted by training and must be replenished 5. Proper amount and timing of CHO before, during, and/or after exercise II. 4.1 Carbohydrates in food • Carbohydrates are found as single sugars (monosaccharides), two linked sugar molecules (disaccharides), or many sugar molecules linked together (polysaccharides). • Carbohydrates vary in their sweetness and in the blood glucose and insulin response to their consumption. • Carbohydrates are often classified as simple sugars and starches, or complex carbohydrates. • Carbohydrates of different types should not be considered good or bad, but appropriate or inappropriate considering the athletes’ goals and general health. A. Carbohydrates are found in various forms in food. 1. Monosaccharides a. Glucose b. Fructose c. Galactose 2. Disaccharides a. Sucrose (glucose + fructose) b. Lactose (glucose + galactose) c. Maltose (glucose + glucose) 3. Polysaccharides a. Chains of glucose b. Starch, fiber, glycogen c. Fiber is indigestible 1) When whole grains are processed, fiber is removed 2) Good sources of fiber: whole grains, legumes, seeds, fruits, vegetables 4. Spotlight on... Sugar Alcohols a. Formed from mono- and disaccharides b. Glycerol, sorbitol, mannitol, xylitol c. “Low-impact carbs” 1) Marketing term indicating slow absorption 2) Glucose and insulin concentrations rise slowly d. Sorbitol and mannitol are incompletely absorbed 1) Fewer kcal/g than sucrose or fructose 2) May have laxative effect B. Carbohydrates are classified in different ways. 1. No single way to classify a. Sugars vs. starches b. Simple vs. complex c. Minimally processed (“quality”) vs. highly processed d. “Good” vs. “bad” Questions for discussion: (1) Under what circumstances might it be appropriate for an athlete to consume simple sugars? (2) Why is it important for people to consume fiber if humans lack the enzymes to digest it? III. 4.2 Digestion, absorption, and transportation of carbohydrates • Digestion of carbohydrates begins in the mouth but mostly occurs in the small intestine. • Specific digestive enzymes break complex carbohydrates down into disaccharides and, finally, monosaccharides. • The monosaccharides glucose, fructose, and galactose are absorbed from the small intestine into the blood using specific protein transporters found in the intestinal cell membrane. • Glucose and galactose are absorbed into the intestinal epithelial cells by active transport by a sodium and glucose transporter (SGLT) and into the blood by facilitated diffusion through the GLUT-2 glucose transporter. • Fructose is absorbed into the intestinal epithelial cell by facilitated diffusion by the GLUT-5 transporter and into the blood by the same process and transporter (GLUT-2) as glucose. • Regardless of the type of carbohydrate consumed, most carbohydrate is transported through the body in the blood as glucose. A. Digestion 1. Begins in the mouth and stomach 2. Predominantly occurs in the small intestine 3. Starches are broken down to glucose 4. Disaccharides are broken down to monosaccharides by specific enzymes B. Glucose and fructose are absorbed by different mechanisms. 1. Glucose absorption a. Carrier dependent b. Active transport c. Portal vein to liver, circulates in blood 2. Fructose absorption a. Carrier dependent, with a limited number of carriers b. Concentration gradient c. Portal vein to liver d. Trapped in liver and converted to glucose C. Carbohydrate is transported as blood glucose. Questions for discussion: (1) What happens when someone consumes carbohydrate in excess of what can be absorbed from the small intestine? (2) What happens to fructose and galactose molecules that are absorbed from the small intestine into the blood? IV. 4.3 Metabolism of glucose in the body • The body normally maintains blood glucose within a fairly narrow range, approximately 70 to 110 mg/dl. • The pancreas is a major organ controlling blood glucose through its ability to secrete insulin and glucagon. • Glucose circulating in the blood is taken up into various tissues through glucose transporters (GLUT) found in their cell membranes. • Glucose transport into tissues is dependent upon the presence and action of insulin in some instances but is not dependent on insulin in other instances. Glucose uptake into skeletal muscle at rest is insulin-dependent, but during exercise glucose uptake is not dependent upon insulin. • Consumption of different carbohydrate foods results in varying responses of blood glucose and insulin, and the scale developed to describe these responses is the glycemic index. • When glucose is taken up into a cell, it can be either used immediately for energy or stored as glycogen for later use. • If carbohydrates are consumed in excess, products of glucose metabolism may be used to produce fatty acids and store energy as fat. • The liver can produce glucose from a number of sources such as lactate, amino acids, and glycerol by gluconeogenesis. A. Blood glucose is carefully regulated. 1. Normal range: 70-110 mg/dl 2. Homeostasis (equilibrium) is hormonally controlled 3. Insulin secreted in response to hyperglycemia 4. Glucose transporters (GLUT) in cell membranes facilitate entry of glucose into cells a. Brain, liver, and exercising muscle cells can take up glucose without insulin b. GLUT-4 – most abundant, responds to insulin c. GLUT-4 participates in insulin-dependent glucose transport 5. Glucagon secreted in response to hypoglycemia a. Hypoglycemia: < 50 mg/dl 6. Insulin and glucagon are counter-regulatory 7. Glycemic effect of various carbohydrates and the glycemic index a. Glycemic response 1) Effect on blood glucose and insulin concentrations b. Spotlight on... Glycemic Index (GI) 1) Classification of CHO foods based on glycemic response 2) High GI a) Blood glucose and insulin concentrations rise quickly b) Highly refined starchy foods and starchy vegetables 3) Low GI a) Blood glucose and insulin concentrations rise slowly b) Legumes, beans, and nonstarchy vegetables B. Glucose can be metabolized immediately for energy. 1. Process depends on energy need of cell and enzymatic capability 2. Red blood cells must use glucose (no mitochondria) 3. Fast-twitch muscle fibers prefer to use CHO via anaerobic glycolysis 4. Slow-twitch muscle fibers prefer to use CHO via aerobic metabolism C. Glucose can be stored as glycogen for later use. 1. If energy need of cell is low, stored as glycogen 2. Insulin (fed state) favors glycogen storage 3. Glycogen depletion favors glycogen storage 4. Glycogen synthase is the primary enzyme D. Products of glucose metabolism can be used to synthesize fatty acids. 1. Not likely to occur if training because glycogen storage is favored 2. More likely to occur in sedentary people who over-consume kcal and CHO 3. Glucose is indirectly stored as fat a. Glucose converted to acetyl CoA and incorporated into fatty acids (lipogenesis) b. Fatty acids stored in adipose tissue E. Glucose can be produced from lactate, amino acids, and glycerol by a process called gluconeogenesis. 1. Limited ability to produce glucose from non-CHO sources a. Lactate to glucose (Cori cycle in liver) b. Amino acids to glucose (e.g., alanine in liver) c. Glycerol to glucose (limited ability in liver) Questions for discussion: (1) How does the body respond when blood glucose rises after consuming a carbohydrate meal? (2) How does the body maintain blood glucose when a person goes for a long period of time without eating, such as when sleeping? V. 4.4 Carbohydrates as a source of energy for exercise • Exercising muscle prefers to use muscle glycogen as its source of carbohydrate for metabolism. • Muscle glycogen may be depleted and fatigue may occur after 60 or more minutes of exercise at a hard aerobic intensity. • Exercise has a strong insulin-like effect, stimulating the uptake of glucose from the blood. • Exercise stimulates the breakdown of liver glycogen to release more glucose into the blood and stimulates the production of more glucose by the liver by gluconeogenesis. • The breakdown of liver glycogen, glycogenolysis, and the increase in gluconeogenesis during exercise is stimulated by the hormone glucagon, secreted by the pancreas. • As exercise intensity increases, the proportion of energy derived from carbohydrate metabolism increases. A. Exercising muscle first uses carbohydrate stored as glycogen. 1. Exercising muscle prefers to use glycogen even when blood glucose is available 2. Muscle glycogen depletion is associated with fatigue B. Exercising muscle takes up and metabolizes blood glucose. 1. Exercise has an insulin-like effect 2. Homeostasis is maintained initially by: a. Glycogenolysis in liver b. Gluconeogenesis in liver 3. Pathways are limited so blood glucose concentration can decline with prolonged exercise 4. Exercising muscle prefers to use glycogen over blood glucose C. Exercise training increases the capacity for carbohydrate metabolism. 1. Aerobic training increases aerobic capacity of muscle a. Increased number and size of mitochondria b. Increased oxidative enzyme activity c. Increased muscle glycogen stores d. Enhanced oxidative capacity increases fat utilization as well 2. “Depletion workouts” or “training low” strategy – intended to enhance fat metabolism a. Training with low carbohydrate stores (via dietary CHO restriction) b. May increase mitochondrial function c. May be difficult to train with low CHO stores d. May compromise immunity D. Glucose metabolism during exercise is controlled by hormones. 1. Glucagon a. Stimulates break down of liver glycogen b. Stimulates gluconeogenesis 2. Epinephrine and norepinephrine a. Stimulate glycogen breakdown b. Stimulate gluconeogenesis 3. Cortisol a. Stimulates amino acid breakdown and gluconeogenesis E. Exercise intensity affects carbohydrate metabolism. 1. As exercise intensity increases % energy from CHO increases 2. CHO is main source of energy for moderate- to high-intensity exercise F. Focus on research: How Does Carbohydrate Consumption Improve Endurance Exercise Performance? Questions for discussion: (1) What effect does the consumption of a sports drink have on the use of glycogen by skeletal muscle during endurance exercise? (2) What happens to the level of insulin in the blood during endurance exercise? Why? VI. 4.5 Carbohydrate recommendations for athletes • The recommended daily intake of carbohydrates for athletes is 5 to 10 g/kg, depending upon the intensity and duration of training and competition, although ultra endurance athletes may need more during certain training periods. • Carbohydrate intake should be adjusted according to sport specific needs as well as training and competition levels. • The amount of carbohydrate in an athlete’s diet should be based upon body weight and not a percentage of the overall diet to ensure adequate intake. • In order to optimize the body’s stores, a carbohydrate-containing meal should be eaten 1–3 hours before training or competition. The timing of the meal and the amount and type of carbohydrate should be individualized. • Thirty to 60 grams of carbohydrate should be consumed each hour during prolonged or high-intensity intermittent exercise. • If exercise has been prolonged and/or is intense enough to result in substantial muscle glycogen depletion, carbohydrate should be consumed as soon as possible after exercise to stimulate the resynthesis of muscle glycogen. • Pre-exercise muscle glycogen stores can be maximized by manipulating exercise and carbohydrate content of the diet in the days before a competitive event in a process called carbohydrate loading. • Endurance or high-intensity training may be impaired if insufficient carbohydrate is consumed and the body’s carbohydrate stores are lowered. A. Daily carbohydrate intake is based upon individual needs to meet the long-term demands of training and competition. 1. General CHO recommendation: 5-10 g/kg body weight daily 2. Fine-tuning of general recommendation needed to match training demands 3. Replenishment of depleted glycogen stores a. 5 g/kg/day is the minimum needed to replenish b. 5-7 g/kg/day recommended for power (strength) athletes c. 5-7 g/kg/day does NOT completely restore to pre-exercise levels for endurance athletes in heavy training d. Endurance athletes in heavy training may need 8-10 g/kg/day e. Intermittent, high-intensity athletes in heavy training have similar needs to endurance athletes f. Ultra endurance athletes may need more than 10 g/kg/day at times 4. Expressing CHO recommendations a. g/kg/day preferred b. % of total energy intake may be used if energy intake is adequate B. Athletes need to plan their carbohydrate intake before, during, and after training and competition. 1. Intake prior to training and competition a. Beneficial for endurance athletes and those in “stop and go” sports b. Amount and timing are related 1) “Rule of thumb” = 1 g/kg one hr prior to exercise, 2 g/kg 2 hr prior 2) Glycemic index is not an issue for most athletes 3) May be convenient to consume CHO in liquid form – Considerations should be made for the form of CHO and convenience 4) Trial and error is important 2. Intake during exercise training and competition a. Beneficial for endurance and ultra endurance athletes b. May be beneficial for those in “stop and go” sports c. General recommendations 1) 30-60 g CHO per hour 2) CHO concentration of 6-8% (60-80 g in 1,000 ml) 3) Spotlight on... Sports Drinks, Bars, and Gels – Available forms of CHO 4) Presence of other nutrients before & during competition/effects on performance 5) Trial and error is important 3. Intake after training and competition a. Ideal physiological environment for restoring muscle glycogen b. General recommendations 1) CHO consumption as soon as practical after exercise 2) Meal size: Small, frequent CHO-containing meals 3) Type of CHO: CHO foods with a high glycemic index 4) For maximum resynthesis: 1.5 g/kg within the first hour and 0.75-1.5 g/kg each hour for the next three hours 5) Addition of protein or amino acids C. Muscle glycogen stores can be maximized by diet and exercise manipulation. 1. Carbohydrate loading – Also known as carbohydrate supercompensation 2. Used by endurance athletes and some body builders 3. Goal is to obtain maximum muscle glycogen storage 4. “Classical” approach was to severely deplete and then replete 5. “Modified” approach eliminates severe depletion stage 6. General recommendation: 10 g/kg/day 3 days prior to event D. Training and performance may be impaired if insufficient carbohydrate is consumed. 1. Adequate daily energy intake is important 2. Most athletes do not meet CHO recommendations 3. Insufficient CHO intake leads to low muscle glycogen levels 4. Acute and chronic fatigue may result from low CHO intake 5. Adequate CHO may reduce risk for immune system suppression in endurance athletes E. Carbohydrate and fiber must be consumed in appropriate amounts for good health. 1. Recommendation for general population: 45-65% of total energy intake 2. Fiber recommendation: 25 g daily for females; 38 g daily for males Questions for discussion: (1) If an athlete needs to replace muscle glycogen quickly, what is the amount, timing, type, and pattern of carbohydrate intake that should be planned? (2) When is it important for an athlete to consider the glycemic index of foods to consume? VII. 4.6 Translating daily carbohydrate recommendations to food choices • Athletes must plan carefully to ensure adequate intake of carbohydrates on a daily basis. • Having carbohydrate-rich foods available increases the likelihood of making good food choices and adhering to the dietary plan for carbohydrate intake. • Athletes must be knowledgeable about making good food and carbohydrate choices when dining out. • Vegetarian diets typically contain a high percentage of carbohydrate-rich foods but care must be taken to consume an adequate total amount of carbohydrates. • Carbohydrate intake in the diet may be influenced by individual situations, such as lactose intolerance, fructose intolerance, or altered glucose and/or insulin responses (for example, diabetes or pre-diabetes). A. A carbohydrate-rich diet requires planning. 1. Meeting CHO needs daily takes some planning 2. Calculations may be made based on kg of body weight 3. Number of serving per food group may be helpful a. Fruits b. Vegetables c. Grains d, Beans e. Milk f. Sugar B. Diet planning for carbohydrate intake must consider practical issues. 1. Having CHO-rich food available 2. Choosing CHO-rich meals in fast-food and other restaurants 3. Vegetarian diets: Many choices a. Some vegetarians consume animal products (e.g., dairy) b. Vegans exclude all foods of animal origin c. Well-planned vegetarian diets are healthful and appropriate for athletes 4. Sugar intake and the use of artificial sweeteners a. High sugar intake may increase risk for some chronic diseases (controversial) b. Exceptionally high intake of high-fructose corn syrup is a concern c. Most adults use some artificial sweeteners d. Safety of artificial sweeteners has always been controversial e. Artificial sweeteners have not been the panacea once hoped for 5. Lactose intolerance a. Lactase activity declines substantially in most people by adulthood b. Intolerance to lactose develops due to low levels of lactase c. Results in gas, bloating, and gastrointestinal upset d. Trial and error to establish tolerance to lactose-containing foods 6. Fructose intolerance a. Similar symptoms to lactose intolerance or IBS b. Results from presence of unabsorbed fructose in GI tract, which attracts water and provides substrate for bacterial fermentation c. Fructose is absorbed better with equal amounts of sugar, but worse when accompanied by sorbitol (a sugar alcohol) 7. Diabetes a. Some world-class athletes have diabetes b. Exercise is beneficial for those with diabetes c. Reactive hypoglycemia C. Spotlight on a real athlete: Lucas, A Cross Country Runner Questions for discussion: (1) Identify at least five carbohydrate-rich foods that are easy to store and prepare. (2) Why might a vegetarian athlete who is getting 70 percent of total calories from carbohydrate not be getting a sufficient amount of carbohydrate in his or her diet? VIII. Summary and review A. Chapter summary B. Post-test assessment C. Review questions D. References Supplementary Teaching Materials and Classroom Activities Note: The text chapter includes an application exercise featuring a contestant in the Chicago Marathon (p. 128). Activity 4-1 Have each student calculate a minimum daily carbohydrate (CHO) intake for an athlete in training. Based on the athlete’s particular sport, have students estimate the amount of carbohydrate needed during each mesocycle—preparation, competition, and transition (see Chapter 1, Activity 1-2). 1. Calculate minimum daily CHO intake. 2. Calculate recommended CHO intake for each mesocycle. Sample answers based on a 60-kg athlete: 1. Calculate minimum daily CHO intake. 5 g CHO/kg × 60 kg = 300 g 2. Calculate recommended CHO intake for each mesocycle. Preparation: 6 g CHO/kg × 60 kg = 360 g Competition: 8 g CHO/kg × 60 kg = 480 g Transition (“off season”): 5.5 g CHO/kg × 60 kg = 330 g Note: These figures are a reflection of the athlete’s training plan (not shown). Activity 4-2 This activity helps to illustrate that an athlete’s CHO intake should be periodized rather than consistent over the long term. Have each student determine an appropriate amount of carbohydrate for an athlete for the periods listed. Assume that the athlete is not restricting energy intake or trying to change body composition. If general recommendations are given as a range, students should briefly explain why they chose the recommendation that they did. Calculations are needed to translate the g/kg recommendation to total g of CHO. Time period CHO recommended (g/kg) Actual CHO needed Two months prior to competition Week prior to competition Pre-event meal During exercise (if needed) After exercise Sample answers based on a 70-kg, male, highly ranked recreational tennis player preparing for a league-ending tournament: Time period CHO recommended (g/kg) Actual CHO needed Two months prior to competition 6 g/kg/day based on 1.5 hours of training or match play, four days per week 420 g/day Week prior to competition 8 g/kg/day to maximize muscle glycogen stores prior to league-ending tournament 560 g/day Pre-event meal If start time is known, 2 g/kg 2 hours prior due to nervousness. 140 g During exercise (if needed) 0.5 g/kg/hour if match lasts more than 1.5 hours, consumed as a sports drink. Previously established through trial and error. 35 g After exercise 1.5 g/kg in the first hour after exercise to prepare for next match. 105 g in the first hour post-match Activity 4-3 One of the most popular methods for students to learn about nutrients is to have them evaluate 24-hour dietary intake over a period of 1 to 3 days. Typically, near the beginning of the course students are asked to record their food and beverage intake over a three-day period and enter the data into the computer program that accompanies the textbook. By printing the reports analyzing each day’s intake and the average intake over a three-day period, students have ready access to nutrient data that can be compared and contrasted with recommended guidelines. Unfortunately, many students will not be in training and their current intake does not reflect a highly trained athlete’s goals or requirements. There are numerous in-class activities available if students have completed the dietary analysis and bring it to class. Some suggested activities include having students: 1. Identify foods consumed that are primarily sugars and starches. 2. Distinguish foods consumed based on commonly used terms and discuss whether such terms are helpful—simple vs. complex carbohydrates, minimally vs. highly processed, “good” vs. “bad.” 3. Identify foods high in fiber. 4. Identify “go to” carbohydrate foods—foods that are familiar, readily available, and/or easy to prepare or eat. 5. Identify carbohydrate foods that are nutrient dense. Thorough evaluation of the dietary analysis to determine if carbohydrate needs were met or well matched to the training cycle requires more time and is generally completed outside of class. If students have completed Activity # 2 then they can determine if daily carbohydrate goals were met and if carbohydrate intake prior to, during, or after exercise was appropriate. It can also be helpful to have students create a diet from “scratch” that meets the goals for a day in an athlete’s most demanding training period. Many students enjoy entering foods into the computer program and creating a daily diet. To help students view diet planning from a perspective that is different than their own, suggest that they create a diet for someone with a vastly different weight. For example, a 220-lb person would be assigned to create a diet for a 100-lb gymnast, while a 110-lb person would be assigned to create a diet for a 290-lb lineman. Such an assignment can help students become more aware of appropriate portion sizes. Activity 4-4 Some students (and instructors) have had personal experiences with carbohydrate intake and athletic performance that they are willing to share. Topics could include: 1) inability to finish a race due to near muscle glycogen depletion, 2) dizziness or fainting due to low carbohydrate intake, 3) gastrointestinal distress before, during, or after competition, 4) experiences with severe carbohydrate loading methods, or 5) using a very low-carbohydrate diet for weight loss. Crossword Puzzle Answer Key 1. glycemic 2. glycogenolysis 3. germ 4. hyperglycemia 5. galactose 6. fructose 7. cellulose 8. sucrose 9. insulin 10. endosperm 11. gluconeogenesis 12. lactose 13. maltose 14. bran Word Find Puzzle Answer Key • 3 elements found in carbohydrates: carbon, hydrogen, oxygen • 6 sugars found in foods: glucose, fructose, galactose, maltose, sucrose, lactose • 3 types of foods rich in starch: grains, legumes, tubers • 3 substrates for gluconeogenesis: lactate, amino acids, glycerol • 5 hormones involved in blood sugar regulation: insulin, glucagon, epinephrine, norepinephrine, cortisol • 3 fresh fruits/vegetables that last a while: apples, bananas, carrots • 3 high-carbohydrate restaurant choices: baked potato, vegetarian burrito, fruit smoothie D B O B N M A L T O S E S E M U G E L G A L A C T O S E T K N N O W W H N Y I N L K O V E A M I N O A C I D S I E Y A O E U L I K E I G D O A A L L R G C N T D H E C H A A S U C R O S E H L O A P P L E S N C G E S Y B O U P P U R S U O T F R U I T S M O O T H I E C T H M T E T L H R O U G H N T O N N O I Y O A O G L Y C E R O L K M Y S I S S D M T O N E Y M Y C I G A R E U P E O R N O R E P I N E P H R I N E L E T L O T E S O X Y G E N I H A V T I E T N G T S E E N T R H E W O R S A N T U V E G E T A R I A N B U R R I T O O B F N I T Y E T I I W A N T T O C K N E L A C T O S E O N W S T O R R A C C R A N F R U C T O S E Y O U T E L L L S Chapter 4 Crossword Puzzle Across Down 5. Monosaccharide found naturally in food as part of the disaccharide lactose. 8. A disaccharide made of glucose and fructose. 11. The manufacture of glucose by the liver from other compounds such as lactate, protein, and fat. 12. Disaccharide found naturally in milk. 13. Sugar produced during the fermentation process that is used to make beer and other alcoholic beverages. 14. The husk of the cereal grain. 1. The effect that carbohydrate foods have on blood glucose concentration and insulin secretion is known as the _____ response. 2. The breakdown of liver glycogen to glucose and the release of that glucose into the blood. 3. When referring to grains, the embryo of the plant seed. 4. Elevated blood glucose. 6. Monosaccharide found naturally in fruits and vegetables. 7. The main constituent of the cell walls of plants. 9. A hormone produced by the pancreas that helps to regulate blood glucose. 10. Tissue that surrounds and nourishes the embryo inside a plant seed. Chapter 4 Word Find Puzzle D B O B N M A L T O S E S E M U G E L G A L A C T O S E T K N N O W W H N Y I N L K O V E A M I N O A C I D S I E Y A O E U L I K E I G D O A A L L R G C N T D H E C H A A S U C R O S E H L O A P P L E S N C G E S Y B O U P P U R S U O T F R U I T S M O O T H I E C T H M T E T L H R O U G H N T O N N O I Y O A O G L Y C E R O L K M Y S I S S D M T O N E Y M Y C I G A R E U P E O R N O R E P I N E P H R I N E L E T L O T E S O X Y G E N I H A V T I E T N G T S E E N T R H E W O R S A N T U V E G E T A R I A N B U R R I T O O B F N I T Y E T I I W A N T T O C K N E L A C T O S E O N W S T O R R A C C R A N F R U C T O S E Y O U T E L L L S Instructions: In the grid above, find the following words or phrases, and then write them beside each clue. • 3 elements found in carbohydrates: • 6 sugars found in foods: • 3 types of foods rich in starch: • 3 substrates for gluconeogenesis: • 5 hormones involved in blood sugar regulation: • 3 fresh fruits/vegetables that last a while: • 3 high-carbohydrate restaurant choices: Instructor Manual for Nutrition for Sport and Exercise Marie Dunford, J. Andrew Doyle 9781285752495
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