Chapter 4 Lecture Slides

Transcription

1 Chapter 4 Lecture Slides Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Dietary Carbohydrates One of the most important nutrients in your diet, from the standpoint of both health and athletic performance, is dietary carbohydrate. What are the different types of dietary carbohydrate? Carbohydrates Carbon, hydrogen and oxygen Simple carbohydrates Monosaccharides Name them Disaccharides Name them and the monosaccharides for each 1

2 Figure 4.1 Types of carbohydrate Complex carbohydrates Polysaccharide Glucose polymer Total fiber Dietary fiber Nondigestible carbohydrates and lignin Intrinsic and intact in plants Definition includes accompanying phytochemicals Functional fiber Nondigestible carbohydrates with beneficial health effects Extracted from foods; may be added to other foods Types of dietary carbohydrate 2

3 What are some common foods high in carbohydrate content? Other sources of carbohydrates Added sugars How much carbohydrate do we need in the diet? Recommended Dietary Allowance (RDA) 130 grams Acceptable Macronutrient Distribution Range (AMDR) 45-65% of energy intake Daily Value (DV) 60% of daily energy needs 300 grams on a 2,000 Calorie diet 25 grams of fiber 3

4 Recommended carbohydrate in the diet? Adequate Intake (AI) for total fiber Men 38 grams up to age grams over age 50 DV not adequate Women 25 grams up to age grams over age 50 Fiber in food Recommended carbohydrate in the diet? Recommendations for added sugars NAS: 25% of total Calories Health professionals: 10% of total Calories 4

5 Recommended carbohydrate in the diet Sport nutritionists Recommend high end of AMDR 60-70% or higher Diet containing 3,000 Calories 450 grams of carbohydrate at 60% level Digestion Enzymic activity Absorption Diffusion Facilitated diffusion Active transport Metabolism and Function Figure 4.4 5

6 Figure 4.5 How are dietary carbohydrates digested and absorbed and what are some implications for sports performance? Enzymic activity Some implications for sport Rate of gastric emptying Multiple receptors for monosaccharides Sodium-glucose co-transport High concentrations of simple sugars Gas producing carbohydrate foods What happens to the carbohydrate after it is absorbed into the body? Most dietary carbohydrates eventually are converted to glucose which circulates in the blood Carbohydrate foods have different effects on blood glucose levels The glycemic index and glycemic load 6

7 The Glycemic Index (GI) The glycemic index (GI) A ranking system relative to the effect consumption of 50 grams of a specific carbohydrate has on blood glucose The blood glucose response to 50 grams of glucose is ranked at 100 GI rating scale 70 or more High GI foods Medium GI foods 55 or less Low GI foods The Glycemic Load (GL) The glycemic load (GL) A ranking system relative to the effect consumption of carbohydrate has on the blood glucose level, but incorporates the portion size, such as 4 ounces. The GL is calculated by the following formula: Glycemic index and glycemic load 7

8 Glycemic index and glycemic load Glycemic index and glycemic load What is the metabolic fate of blood glucose? Normal blood glucose = mg/dl, or milligram percent High GI or GL foods may lead to hyperglycemia (>140 mg/dl) Insulin response Move blood glucose into body cells May be a reactive hypoglycemia (<40-50 mg/dl) 8

9 Insulin and GLUT-4 receptors Insulin and GLUT-4 receptors Fates of blood glucose May be used for energy May be converted to liver or muscle glycogen May be converted to and stored as fat in adipose tissues May be excreted in the urine if in excess 9

10 Figure 4.6 How much total energy do we store as carbohydrate? Expressed as millimoles in scientific journals Carbohydrate storage in the body 10

11 Can the body make carbohydrates from protein and fat? The process of gluconeogenesis From protein metabolism Glucose-alanine cycle About 0.56 g glucose from 1 g protein From fat metabolism Glycerol (about 10% or triglyceride) 1.0 g of glucose from 1 g glycerol From by-products of carbohydrate metabolism Lactate and the Cori cycle 0.5 g glucose from 1 g lactate Figure 4.8 What are the major functions of carbohydrate in human nutrition? To supply energy Essential for brain metabolism Very important fuel for many sports Other functions Glycoproteins Ribose in DNA and RNA 11

12 Figure 4.9 Carbohydrates for Exercise Carbohydrate as an energy source during exercise Effect of training on carbohydrate metabolism Methods of providing carbohydrate Before competition During competition After competition During training In what type of activities does the body rely heavily on carbohydrate as an energy source? Carbohydrate contributes about 40% of energy needs at rest Fat is main energy source during low exercise intensity, such as 40-50% VO2max Carbohydrate is major source during Very high intensity anaerobic exercise High intensity (>65% VO2max) aerobic exercise Prolonged aerobic exercise events Intermittent high-intensity exercise sports 12

13 Why is carbohydrate an important energy source for exercise? May be used both anaerobically and aerobically Yields 5.05 Calories from one liter of oxygen ATP production per unit of oxygen consumed 2.7 ATP from carbohydrate 2.3 ATP from palmitic fatty acid Metabolic pathways for carbohydrate more efficient Muscle glycogen very important source Liver glycogen converted to blood glucose Blood glucose delivered to muscles Carbohydrate sources for exercise Muscle glycogen is a very important source Liver glycogen is converted to blood glucose Blood glucose is delivered to muscles What effect does endurance training have on carbohydrate metabolism? Endurance training has several beneficial effects on exercise metabolism Increase in VO2max Increase in ability to exercise at a higher % of VO2max without fatigue 13

14 Exercise training and carbohydrate metabolism Effect on lactic acid production Decrease production during standardized exercise Increased clearance by liver, heart and active muscles Increase in insulin sensitivity of muscles More glycogen is stored in the muscle Muscle increases its capacity to oxidize carbohydrate Increase in GLUT-4 transporters GLUT-4 receptors kept in reserve until needed; then translocated to the cell membrane As noted in chapter 5, the body also increases its ability to oxidize fat during exercise How is hypoglycemia related to the development of fatigue? Gluconeogenesis cannot keep pace with glucose utilization during prolonged, high-intensity aerobic exercise Depletion of liver glycogen eventually leads to hypoglycemia Normal blood glucose ( mg/100ml) Hypoglycemia (,45 mg/100ml) Hypoglycemia can impair functioning of the central nervous system, the brain Feelings of weakness, fatigue 14

15 Hypoglycemia The human body attempts to prevent hypoglycemia Hormone activity Insulin Epinephrine Glucagon Cortisol Hormones and glucose metabolism Hormones and glucose metabolism Hormone Gland Stimulus Action Insulin Pancreas Increase in blood glucose Glucagon Pancreas Decrease in blood glucose; exercise stress Epinephrine Adrenal Exercise stress; decrease in blood glucose Cortisol Adrenal Exercise stress; decrease in blood glucose Helps transport glucose into cells; decreases blood glucose levels Promotes gluconeogenesis in liver; helps increase blood glucose levels Promotes glycogen breakdown and glucose release from the liver Promotes breakdown of protein; stimulates gluconeogenesis 15

16 How is lactic acid production related to fatigue? Lactic acid production is associated with highintensity anaerobic exercise The current thinking is that the dissociated hydrogen ion and increased acidity, not lactate itself, is the cause of fatigue Lactate may be used as fuel during exercise The lactate shuttle George Brooks Lactate shuttles from white muscle to oxidative red muscle Sports drink - Polylactate How is low muscle glycogen related to the development of fatigue? Low muscle glycogen and aerobic exercise Muscle glycogen is the primary fuel for endurance athletes, such as marathon runner Studies have shown physical exhaustion to be associated with very low muscle glycogen levels. However, other studies have shown fatigue with some muscle glycogen remaining. Muscle fatigue in aerobic exercise with some glycogen remaining Suggested mechanisms Location: Glycogen may be located in the muscle fiber where it cannot be used Rate of energy production: Not enough glycogen for millisecond energy needs Muscle fiber type: May be depleted in type I; type II fibers require more mental effort to recruit Use of fat for energy: Muscle may need to rely on fat, which is less efficient as an energy source Role of the brain: Low muscle glycogen may send a signal to the brain 16

17 Low muscle glycogen and anaerobic exercise Low muscle glycogen may not impair high-intensity anaerobic exercise if there is adequate glycogen in the white muscle fibers Prolonged anaerobic exercise, such as 3 minutes, may be adversely affect by low muscle glycogen in the fast twitch fibers Field research suggests muscle glycogen depletion in fast twitch muscle fibers may contribute to slower sprint speeds in the latter states of high-intensity intermittent exercise sports, such a soccer. How are low endogenous carbohydrate levels related to the central fatigue hypothesis? The central fatigue hypothesis Low muscle glycogen and blood glucose will stimulate gluconeogenesis from protein Branched chain amino acids (BCAA) are a main source Blood levels of BCAA decline As BCAA levels drop, free tryptophan (ftrp) increases A high ftrp:bcaa ratio favors entry of ftrp in the brain Brain TRP increases serotonin, which is related to fatigue symptoms Adequate carbohydrate will help prevent the decline in BCAA Central fatigue hypothesis 17

18 Will eating carbohydrate immediately before or during an event improve physical performance? Endogenous carbohydrates Importance of initial body stores Adequate for minutes of aerobic exercise Exogenous carbohydrate To help improve performance, exogenous carbohydrate intake must be able to delay the onset of fatigue that would otherwise occur as a result of premature depletion of endogenous carbohydrate sources. Other factors may explain beneficial effects of exogenous carbohydrates; research with oral sensation Effects of exogenous carbohydrate on exercise performance of different intensity and duration Very high-intensity exercise for < 30 minutes In general, no effect May benefit athletes in weight-control sports Very high-intensity resistance exercise training In general, no High-intensity exercise for 30 to 90 minutes In general, no Some studies show benefits; possibly beneficial effects on the central nervous system; sprint performance in an overall aerobic event Exogenous carbohydrate and performance: Exercise intensity and duration Intermittent high-intensity exercise for minutes Some studies show beneficial effects on performance, particularly in the latter stages of the protocol Some beneficial effects from field studies High- to moderate-intensity exercise greater than 90 minutes Generally, research supports a beneficial effect Maintain blood glucose concentrations to help sustain high rates of carbohydrate oxidation 18

19 Timing of carbohydrate intake Four hours or less before exercise Possible beneficial effects if taken 1-4 hours before Less than 1 hour before exercise Research findings somewhat ambiguous Possibility of reactive hypoglycemia in some athletes Most studies show no adverse effects May have some beneficial effects Timing of carbohydrate intake Immediately before exercise Not beneficial if exercise is short in duration May benefit performance in more prolonged aerobic endurance events > 60% VO2max Exercise suppresses secretion of insulin Exercise stimulates secretion of epinephrine During exercise May enhance performance in prolonged aerobic exercise Maintains blood glucose Provides energy to muscles Reduces ratings of perceived exertion Use of ingested carbohydrate Exogenous carbohydrate may be used as an energy source within 5-10 minutes Peak use appears to occur minutes after ingestion May contribute percent of the carbohydrate energy source during, or more in the latter stages of exercise 19

20 Possible fatigue-delaying mechanisms Maintenance of blood glucose levels Most likely mechanism Prevent hypoglycemia Glucose provided to muscle cells Reduction of psychological effort Glucose provides energy to the brain Prevent decrease in BCAA Reduce RPE (ratings of perceived exertion) Possible fatigue-delaying mechanisms Sparing of muscle glycogen Research findings equivocal Positive effects: Spared muscle glycogen in slow-twitch muscle fibers Negative effects: No glycogen sparing even when subjects were maintained hyperglycemic with glucose infusions Limitations to prevent fatigue It appears that the maximal amount of oxidizable exogenous carbohydrate provided during exercise is 1.5 to 1.7 grams per minute, or lower. This is much lower than the required energy needs at 65-85% of VO2max. Elite runners might oxidize 4-5 grams of carbohydrate per minute. 20

21 Optimal supplementation protocol Consume carbohydrates both before and during the exercise task. When, how much, and in what form should carbohydrates be consumed before or during exercise? Athletes who may benefit from carbohydrate intake Endurance exercise Intermediate high-intensity exercise Fluid replacement is also an important consideration 21

22 Pre-exercise: When and how much? 4 hours prior to event 4-5 g CHO/kg body weight 70 kg athlete: grams of carbohydrate 1 hour prior to event 1-2 g CHO/kg body weight 70 kg athlete: grams of carbohydrate Immediately before exercise grams in a concentrated form Some commercial sport/energy drinks During exercise: When and how much When? About every minutes How much? Approximately 1 gram per minute, or about 60 grams an hour Some general recommendations Asker Jeukendrup, University of Birmingham 22

23 Carbohydrate Intake before Competition 4 hours prior 4-5 grams/kg Some lean protein 1 hour prior 1-2 grams/kg Immediately before 1 gram/kg 4 hours before 70 kg runner grams Large bagel (75g) Turkey breast (0g) 4 oz (28 g protein) Orange juice (45 g) 12 oz Yogurt, fruit (50g) 8 oz Banana (30g) Energy drink (80g) 12 oz Types of carbohydrate Carbohydrate combinations Carbohydrate combinations, such as glucose and fructose Use different receptors for absorption Up to gram per minute may be used, or grams per hour May be useful when more than 60 grams per hour is recommended Separate receptors for monosaccharides 23

24 Types of carbohydrate Fructose Fructose theorized to be better than glucose because it is absorbed more slowly, leading to a blunted insulin response and a more stable blood sugar However, effect when ingested before or during exercise is little different from glucose Large amounts may cause diarrhea Types of carbohydrate Solid and liquid carbohydrates Sport drinks; sport gels; sport jelly beans Appears to be little difference between the two forms relative to the effects on performance Preference of the athlete should be considered Types of carbohydrate Low-glycemic-index foods Similar theory as fructose; low-gi foods may help maintain a higher blood glucose level Numerous studies show no significant differences between low-gi and high-gi diets on exercise performance However, several recent studies from Loughborough University show some beneficial effects, such as greater run time to exhaustion at 70% VO2max with a low GI (GI = 37) versus a high GI (GI = 77) diet 24

25 Types of carbohydrate Carbohydrate with protein Several studies have compared the effects of carbohydrate supplementation alone to carbohydrate/protein supplementation on performance following recovery from previous exercise. In general, there is little difference between the treatments on subsequent performance Types of carbohydrate Individuality Some athletes more vulnerable to gastrointestinal distress with various forms or concentrations of carbohydrate Runners are prone to Runner s trots with highly concentrated solutions Experiment with different types and amounts of carbohydrate for your event Train your stomach as you train your muscles; know your limits What is the importance of carbohydrate replenishment after prolonged exercise? Rapid restoration of muscle glycogen important for some athletes Repeated bouts of prolonged, intense exercise on the same day Prolonged, intense exercise on consecutive days 25

26 Carbohydrate replenishment after prolonged exercise In repeated bouts of prolonged, intense exercise with 4-hour interval Consume 1 gram/kg body weight immediately after first event, and also 2 hours prior to the second event. May also consume carbohydrate immediately before and during the second event Carbohydrate replenishment after prolonged exercise In repeated bouts of prolonged, intense exercise on consecutive days Consume about 1.2 to 1.5 grams of carbohydrate per kg body weight every hour for 4-5 hours after exercise. Carbohydrate snacks may be eaten every 30 minutes. Carbohydrate and protein replenishment after prolonged exercise Some early research suggested combining carbohydrate with protein would increase muscle glycogen resynthesis. However, recent research indicates that if equivalent energy from carbohydrate and carbohydrate/protein supplements are provided, there is no additive effect of the protein. As noted in chapter 6, providing protein after exercise may provide some benefits. 26

27 Carbohydrate-rich diets for athletes Sport nutritionists recommend that athletes consume about 8-10 grams of carbohydrate per kilogram body weight daily For a 70-kg athlete, this would amount to 560 to 700 grams of carbohydrate daily, or the equivalent of 2,240 to 2,800 Calories On a 3,500-Calorie daily intake, the carbohydrate would provide 65-80% of daily energy intake. This amount of daily carbohydrate would help restore muscle glycogen levels Will a high-carbohydrate diet enhance my daily training? Per kg body weight, sport nutritionists generally recommend about 5-7 grams of carbohydrate daily for athletes in general training, and about 7-10 for endurance athletes Research suggests high-carbohydrate diets may help training both physiologically and psychologically, Not all athletes need very high carbohydrate diets. Even some elite trained endurance athletes may sustain training on lower amounts, but training may be more stressful psychologically. Carbohydrates during training There is no evidence that low-carbohydrate diets improve exercise performance A diet rich in healthy carbohydrates may help guarantee optimal energy sources for daily training Train high and compete high is the concept of training and competing with high carbohydrate intake. 27

28 Carbohydrate Intake During Training Consume a healthy diet at the high end of the AMDR for carbohydrates, or about 60-70% or more of energy from carbohydrate. Focus on meals with a low glycemic load Carbohydrates should fill about 2/3 of your plate during meals. Snacks should be rich in carbohydrates Carbohydrate Intake During Training Some athletes may continue to train effectively with somewhat lower carbohydrate diets, approximating 45% of energy intake. Some recent research suggests training with low glycogen stores may induce gene expression that may enhance training adaptations However, ratings of perceived exertion (RPE) may be higher during training with low carbohydrate intake. Research is too limited to recommend training with low carbohydrate diets. Carbohydrate Intake During Training In general, consume about 6-10 grams of carbohydrate per kilogram body weight, or about 3-5 grams per pound body weight. (1 kilogram = 2.2 pounds). If you train less than 1 hour/day, then about 6-7 grams is sufficient. As your daily training time increases, consume 8-10 grams or more per kilogram body weight. Recommended daily carbohydrate intake, in grams, for endurance athletes. 50 kg 110 lbs 55 kg 121 lbs 60 kg 132 lbs 65 kg 143 lbs 70 kg 154 lbs 75 kg 165 lbs 80 kg 176 lbs 85 kg 187 lbs 90 kg 198 lbs 6-7 g/kg 300 to to to to to to to to to g/kg 400 to to to to to to to to to

29 Carbohydrate Intake during Training Dietary strategies for rapid muscle glycogen restoration Consume carbohydrates immediately after and about every 30 minutes for 4-5 hours post-exercise Consume about 0.6 to 0.8 gram per kilogram body weight Consume carbohydrates with a high glycemic index Consume as either liquids or solids Consume some lean protein as well. The carbohydrate:protein ratio should be about 4:1, or 4 grams of carbohydrate for each gram of protein. This full procedure is not necessary if there is ample time for full recovery, but consuming a carbohydrate:protein combination immediately after exercise is recommended. Carbohydrate loading What is carbohydrate, or glycogen, loading? Method of increasing muscle glycogen levels Also known as muscle glycogen supercompensation What type of athlete would benefit from carbohydrate loading? Athletes who sustain high levels of continuous energy expenditure for prolonged periods Long-distance runners Cross-country skiers Endurance triathletes Tournament play in intermittent high-intensity exercise sports 29

30 How do you carbohydrate load? Athlete should be fully trained Classic procedure not necessary: Depletion stage Low carbohydrate diet Carbohydrate loading Have about 3-4 days of high carbohydrate intake, about 8-10 grams/kg body weight, or more Low and high glycemic index carbohydrates are equally effective Taper exercise training over the course of a week or longer Carbohydrate loading procedures 30

31 Will carbohydrate loading increase muscle glycogen concentration? Most studies report increased muscle glycogen levels following carbohydrate loading procedures Both males and females will increase glycogen levels if adequate energy and carbohydrate are consumed Muscle glycogen levels may increase two to three times above normal Experiment with the protocol during training How do I know if my muscles have increased their glycogen stores? Monitor changes in body weight Approximately 3-4 grams of water are bound to each gram of muscle glycogen An additional grams of glycogen plus 900-1,200 grams of water is 1,200-1,600 grams, or pounds above your normal weight Bodybuilders may use this technique to highlight muscle definition, but research is not supportive of its effects Will carbohydrate loading improve exercise performance? In general, the procedure is not needed for exercise tasks of short duration In general, research supports the use of carbohydrate loading as a means to enhance performance in prolonged endurance exercise tasks Helps maintain an optimal pace longer Extra body water may help during exercise in the heat Most appropriate protocol is to use both carbohydrate loading and consumption of carbohydrate during the event 31

32 Are there any possible detrimental effects relative to carbohydrate loading? The extra body weight could be a disadvantage in running, but this appears to be offset by the increased energy supply. The water may also be beneficial during exercise in the heat. Diabetics should consult their health professional Low-GI foods may be more healthful for some High amounts of simple sugars may contribute to gastrointestinal distress Carbohydrates: Ergogenic Aspects Metabolic by-products Pyruvate DHAP (Pyruvate and dihydroxyacetone) Lactate salts Ribose Multiple carbohydrate products Pyruvate Pyruvate is a 3-carbon by-product of glycolysis Theory: Accelerate the Krebs cycle or use glucose more effectively Efficacy Research is limited, but the available research indicates that supplementation with pyruvate does not enhance endurance performance. Several studies have shown beneficial effects on weight loss in obese subjects 32

33 DHAP Dihydroxyacetone is also a 3-carbon carbohydrate Theory: Increase muscle glycogen content Efficacy Although several studies have shown that DHAP supplementation might enhance aerobic endurance performance in untrained males, no studies are available with trained individuals. Lactate salts Lactate is a small metabolite of glucose; C3H5O3 Converted to pyruvate or glucose Found in a sports drink Cytomax TM Contains alpha-l-polylactate plus fructose, glucose, and glucose polymer Research limited and equivocal Additional research with Cytomax TM recommended Ribose Ribose is a 5-carbon monosaccharide Very little ribose consumed in a normal diet Produced naturally in the body Found in RNA and ATP Theory: Rapid resynthesis of ATP Efficacy: The current data do not support an ergogenic effect of ribose supplementation. Anaerobic cycle ergometer performance Peak power output Maximal knee extension 2,000-meter rowing performance 33

34 Multiple carbohydrate by-products Contain intermediates of the Krebs cycle Limited research, but no beneficial effects on exercise performance or recovery Dietary Carbohydrates Health Implications Recommendations Eat more of the good carbs Complex carbohydrates Total fiber Eat less of the bad carbs Added sugars Highly processed and refined carbohydrates How do refined sugars and starches affect my health? High intake of refined carbohydrates has been alleged to contribute to a number of health problems Psychological behavior Hyperactivity in children PMS Dental caries Inflammation may become systemic Cancer Diabetes 34

35 Refined sugars and starches and health NAS indicated that given the currently available scientific evidence relative to the effect of dietary sugar on dental caries, psychological behavior, cancer, risk of obesity and hyperlipidemia, there is insufficient evidence to set an UL Nevertheless, the NAS did note the theory linking a high-gi diet to certain health problems appears to be valid. It did not set an UL, but recommended a maximum of 25% of energy intake. Some health professional organizations recommend less than 10% of energy intake. Decreasing intake of refined carbohydrates Eat refined starches and grains sparingly. Use mainly as a side dish Read food labels and select foods low in sugar Reduce the sugar in foods prepared at home Eat more fruits for naturally occurring sugars Decrease intake of soft drinks Use other sweeteners such as cinnamon, ginger or artificial sweeteners Are artificial sweeteners safe? Products available Saccharin Aspartame Neotame Sucralose Sugar alcohols Sorbitiol, erythritol, mannitol 35

36 Artificial sweeteners Artificial sweeteners Recent reviews by the FDA and Consumers Union consider all artificial sweeteners to be safe in small amounts. May be helpful in weight control Some caveats: Aspartame and individuals with phenylketonuria High intakes of sugar alcohols may cause diarrhea Why are complex carbohydrates thought to be beneficial to my health? Healthy carbohydrates are an integral part of several healthy diet plans Dean Ornish diet plan; the Pritikin program The OMNI diet plan 36

37 Healthy carbohydrates Healthy carbohydrates Whole grains Fruits Vegetables Legumes Proposed attributes of healthy carbohydrates Low-glycemic foods Various phytochemicals Various vitamins and minerals Dietary fiber Healthy carbohydrates Why should I eat foods rich in fiber? Adequate intake (AI) for total fiber: Based on reduced risk of coronary heart disease 14 grams per 1,000 Calories 38 grams for men age grams for women age

38 Soluble and insoluble fiber The issue of soluble and insoluble fiber Difficult to generalize on different health effects of soluble and insoluble fiber; health effects are due to total fiber, but it may be illustrative to discuss soluble and insoluble fiber effects on health. Proposed health benefits of fiber Water-insoluble fibers are considered to have the greatest effect on fecal bulk Rapid movement through the digestive tract Fiber rich foods are low-gi foods Increase insulin sensitivity Gummy forms of fiber may bind with certain substances in the digestive tract Carcinogens and cholesterol Some water-soluble fibers may be fermented in the large intestine to SCFA SCFA can help reduce serum cholesterol 38

39 Health effects of dietary fiber May help reduce risk of heart disease The reduced glycemic response may be of benefit to treat or prevent diabetes Effect on prevention of colon cancer not as effective as once thought, but some proposed more long-term studies are needed Do some carbohydrate foods cause food intolerance? Lactose intolerance Lactose found in milk and dairy products Individuals with low levels of lactase Gastrointestinal symptoms Need to find alternative source of calcium Fermented daily products (Yogurt) Dark, green leafy vegetables Calcium fortified products (orange juice) Calcium supplements Example of daily food intake to obtain fiber AI Foods Grams of fiber 3 fruits 6 3 vegetables 9 3 slices of whole grain bread 6 ½ cup beans 7 1 serving bran cereal 9 Total daily fiber intake 37 39

40 Gluten intolerance Gluten is a protein found in wheat, rye and barley; the immune system recognizes gluten as a foreign substance Symptoms may be mild, primarily gastrointestinal distress In severe cases, celiac disease causes damage to the lining of the small intestine; medical treatment is necessary Does exercise exert any beneficial effects related to carbohydrate metabolism? Exercise may enhance glucose tolerance and insulin sensitivity Glucose uptake in body cells is elevated for two hours after an endurance exercise bout Effect is insulin-independent May increase GLUT-4 receptors in cell membranes Exercise can increase insulin sensitivity for 16 hours afterwards Exercise believed to be important in the prevention of type 2 diabetes 40