_6-8Carbohydrates2010

_6-8Carbohydrates2010 - This runner comes to you…...

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Unformatted text preview: This runner comes to you…. CrossCross-country runner, in season – 50 kg, 12% body fat Carbohydrates Carbohydrates & Athletes Performance Performance has dropped off Coach asks for nutrition consult Coach asks for nutrition consult Consult: Consult: – Running 5-15 miles/d 5– Energy intake 2300 kcal/d – Carbohydrate 200 g/kg – Goals: coach wants her to lose 7 pounds as says will improve her pace Outline of topics A little history little Types Types of carbohydrate Review Review basics of carbohydrate metabolism Research recommendations: Research & recommendations: – daily, before, during, after exercise daily, » Endurance exercise » Resistance exercise » Single & repeated sprints Some Some “hot topics” Glycemic Glycemic index Training Training with low carbohydrate Novel carbohydrate sources Novel carbohydrate sources Historical view- value of carbohydrate viewto athletic performance 1920’s 1920’s Scandinavia – Low carb diet several days + hi carb increases R & increased endurance An example Carbohydrate Loading study subjects subjects fed either low (25%), medium (50%), or high (75%) carbohydrate (75%) carbohydrate diet diet for 3 days time time to exhaustion at 70% max on bike Muscle Muscle biopsies for content of glycogen time to exhaustion 200 180 160 140 120 100 80 60 40 20 0 * * 1930’s 1930’s Harvard fatigue lab – Exhausted dogs given carb could exercise longer min 1960’s 1960’s development of muscle biopsy technique to look at changes in muscle glycogen 1980’s 1980’s beginning of use of isotopic tracers to examine use of carbohydrate oxidation rates Lo Me Hi Bergstrom et al 1967 Some Some key points discovered by early research Substantial Substantial reduction of muscle/liver glycogen is related to fatigue Use of glycogen is very related to Use of glycogen is very related to exercise exercise intensity & duration Development Development of hypoglycemia during exercise is related to fatigue A little review of Carbohydrate metabolism Especially with regard to exercise Types of carbohydrate Biochemical nomenclature: Biochemical nomenclature: – monosaccharides – disaccharides – polysaccharides AbsorptionAbsorption- a few issues Glucose Glucose absorption is carrier dependent Fructose Fructose uses different carrier and number of carriers are limited – Means might get better carbohydrate delivery if might provide multiple types of carbohydrate id – And, can overload on fructose if consume too much as can’t be absorbed as quickly… GI distress! Common nomenclature: Common nomenclature: – simple carbohydrates – complex carbohydrates Metabolic Metabolic nomenclature: – glycemic index Net: Net: many sports beverages use combination of different carbohydrates and never too much fructose Blood glucose Maintained Maintained at narrow limits (homeostasis) – Normal 4.0-4.5 mmol/L (X 18 to convert to mg%) 4.0mmol/L – Hyperglycemia toxic – Hypoglycemia (<3 mmol/L) can be fatal Hypoglycemia (<3 mmol can be fatal Hypoglycemia < 3mmol/L 3mmol/L Symptoms Symptoms including fatigue, nausea, fatigue, dizziness Impacted Impacted by food intake, hormones, etc – Amount of carbohydrate – Type of carbohydrate Concentration Concentration is balance of entrance and exit – e.g. why hyperglycemia sometimes seen after short, intense exercise? Glycemic Glycemic Response Varies with Different Foods Highly processed starches such as white bread, pasta, or rice have a high GI while beans and legumes have a low glycemic index- even when match total amount of carbohydrate. What influences GI of foods or meals? Form Form of carbohydrate Processing Processing Fat & protein co-ingestion Fat protein co Fiber Fiber content Glycemic Index of some foods higher lower Glucose Glucose White White Bread Potato Potato White White rice Fructose Fructose Legumes Le Dairy Dairy products Most Most fruits Fate of blood glucose Glycemic Index of Selected Foods Can Can be taken up by organs or muscle to be used or stored as glycogen Can Can be taken up by liver for storage as glycogen glycogen or conversion to fat Sports drinks can be low or high…. depends on carbohydrate form Figure 4.16 Blood Blood glucose uptake at muscle Exercise Exercise has “insulin-like” effect to “insulinincrease blood glucose uptake into cell Stimulates Stimulates movement of glucose transporters transporters to cell membrane Muscle glycogen metabolism Can Can be expressed per kg ww or dry weight (~3 fold difference in values depending on units of expression) Can Can not supply glucose to blood [why?] [why?] ~300-400 g of glycogen stored in muscle Rate Rate of use very intensity dependent – If anaerobic ATP generation, glycogen is preferred substrate – Epinephrine stimulates use – Will be used with aerobic metabolism as well but not as rapidly Liver Glycogen Primary Primary role is to provide glucose to blood stream if becomes reduced ~100 ~100 g glycogen stored in liver – More concentrated per gram of tissue than muscle Liver Gluconeogensis Resting, Resting, fed conditions very low Increases: Increases: – Blood glucose drops – e.g. starvation, prolonged exercise Can Can be substantially reduced after overnight fast (to <20 g) Can Can be reduced by exercise if drain on blood glucose is substantial Can Can produce new glucose (gluconeogenesis) (gluconeogenesis) but is costly and slow Decreases: Decreases: – Blood glucose normal or increased – e.g. post feeding A key tool used to study carbohydrate metabolism/use with exercise RER RER ratio (also called RQ or R ratio) Note Note there are other tools to estimate fuel use but beyond scope of this class To calculate total fuels used First First estimate total energy expended Look Look up % as carb & fat in table Calculate energy expended as carb Calculate energy expended as carb & fat fat Part Part of example RER table RER 0.7 .8 .9 1.0 kcal/L 4.686 4.801 4.924 5.047 % carb 0 33.4 67.5 100 % fat 100 66.6 32.5 0 Energy Expenditure and Fuel Utilization During Exercise Bout Apply all this to athletes…. How How affect diet – Daily training diet? – Prior to event? – During exercise? – After exercise? Carbohydrate Intake for Athletes Focus first on endurance athletes Dietary Period Goal of CHO intake Training diet---Training diet---maximize initial glycogen 3-7 d before event---- “ “ Within Within hrs of event---- “ “ event---During event---During event---re-supply glucose as used reAfter event---After event---refill glycogen stores that were used Exp: Training (Daily) Diet Research is used to justify the diet carbohydrate recommendations Provide 1 or 2 example studies and then the overall recommendation Triathletes Triathletes ate regular diet plus given eight carb.supplement drink or placebo Resulted Resulted in 54 vs 68% carbohydrate in diet Simulated Simulated 90 min triathlon then run to exhaustion at 90%max time to exhaustion 7 6 5 * min 4 3 2 1 0 C Pl Millard-Stafford et al 1988 Which part of range do you choose? Training Training diet recommendations 5-10 g/kg carbohydrate in diet (most suggest in the 7-8 g/kg range) 7Typically Typically this is 55-70% of energy 55-70% Goal Goal is to replace glycogen used during training and start each workout with full stores High High intensity but short duration 5-7 g/kg Moderate Moderate intensity & duration or intermittent sports 6-8 Moderate Moderate intensity, long duration 8-10 In In general, lower body weight & total energy expenditure/intake (especially women) will be on lower end of range) Why use g/kg expression vs % of calories? Look at your MyPyramid output Are you in the recommended range for g/kg carbohydrate? Recommendations for Carbohydrate Loading Diet Diet for several days prior to major event Increase glycogen stores of muscle and liver Most Most useful for events over 60 minutes at moderate intensity (65-85% VO2max) (65max) or events of 60 min or more with many repeated repeated intervals of high intensity Classical Carbohydrate Loading Modified Carbohydrate Loading Bergstrom, et al, 1967 Sherman, et al, 1981 Carbohydrate content of pregame meal? meal? Help Help to “top off” glycogen stores Reactive Reactive hypoglycemia if high GI carbohydrate? Research Research shows valuable to have high carbohydrate pre-game meal preDoes Does type of carbohydrate ingested matter? Exp: Glycemic Index of Preexercise Feeding Fed 1 g/kg carbohydrate as lentils, potato, glucose compared to water; fed 1 h before exercise Exercise to exhaustion at 65-70% VO2max. 120 100 80 * min 60 40 20 0 potato water glucose lentils LENTILS maintained: • high glucose • high fatty acids • lower lactate • longer endurance Thomas et al. 1991 Carbohydrate shortly before exercise Later Later research has not clearly shown advantage to low GI meal But…no disadvantage so I sometimes have athletes try moderate GI meals < exercise See latest GSSI sports science exchange (#107) on their web site for recent update on this Goal Goal to “top off” glycogen stores Be Be careful as if still in stomach or in intestine can get GI distress Overall recommendations for carbohydrate 1-4 h before 1exercise exercise if 1if ~ 1-2 h < exercise ingest 1 g/kg If 3If 3-4 h < exercise 3-4 g/kg 3- Carbohydrate during exercise Is it helpful? Which events? How much? Goal to re-supply glucose to reblood stream Exp Study: Carbohydrate During Exercise methods results 7 runners completed runners 2 30 km road races separated by 10d separated by 10d drank drank either water or 5% carbohydrate sol’n before and every 5 km during race Performance Performance time for carb trial was faster (128 vs 131 faster (128 vs 131 min) min) Running Running speed was maintained with carb trial but declined with water Tsintzas et al 1993 Most Most studies find a beneficial effect of carbohydrate consumption during exercise on performance of: Prolonged exercise of greater than 90 min Prolonged exercise of greater than 90 min Moderately Moderately intense @ ~65-85% VO2max ~65??less ??less consistent for shorter “events” but some show benefit for ~60 min maximal effort Recommendations for carbohydrate during exercise Consume Consume a less than 10% carbohydrate solution every 15-20 minutes to supply 15 20 regular source of carbohydrate – Too concentrated slows stomach emptying Plan Plan the pattern to result in ~30-60 g/hr ~30- Maximum rate of glucose oxidation is ~ 1 g/min. Calculate Calculate how much sports drink or food thi this is Many athletes get their much of their carbohydrate before, during and after exercise using sports drinks Get carbohydrate but also electrolytes and fluid that is also important for prevention of dehydration As long as tolerated can use solid foods e.g. bars, gels, cookies, bananas After After prolonged aerobic exercise Goal is to replace liver and muscle glycogen rapidly, especially if a rapidly, subsequent bout How important is it to have carbohydrate during recovery? Accelerates Accelerates replacement of liver and muscle glycogen Issues: Issues: – Timing – Amount – Type Post exercise glycogen resynthesis Can Can take up to 24 hours if severe depletion Carbohydrate Carbohydrate consumption during the first few hours post exercise is important for fastest glycogen synthesis High High glycemic index carbohydrates replace glycogen more rapidly than lower GI Exp Study: Type of carbohydrate post-exercise post5 trained cyclists trained exercised to deplete glycogen For 24 after each For 24 h after each trial trial they consumed CHO at 10 g/kg with either High glycemic index (HGI) or Low (HGI) glycemic index (LGI) (LGI) carbohydrates 120 100 80 60 40 20 0 LGI HGI Rise in muscle glycogen * Recommendations for carbohydrate consumption post exercise Consume 1.2 Consume 1.2 g/kg carbohydrate per carboh hour for first two hours in small frequent meals Choose Choose high glycemic foods Burke et al. 1993 Resistance Resistance exercise Less total energy expended and less total carbohydrate expended Thus, less clear that is advantage to consuming carbohydrate for resistance training performance Is carbohydrate important Is carbohydrate important for for resistance trainers? - carbohydrate loading? - carbohydrate just before/during sets? Single Sprint? Note that we and others have studied this…. Most research does not see benefit of acute carbohydrate ingestion on resistance exercise performance - carbohydrate loading beneficial? beneficial? This is a little more controversial but not a lot of evidence that carbohydrate in training diet or acutely before single sprint acutely before a single sprint improves improves performance Repeated Sprints - carbohydrate loading? - carbohydrate before/during? Evidence Evidence here is more convincing that carbohydrate could be beneficial One One sprint can’t drain glycogen but repeated sprints, especially if part of endurance exercise workout can get to endurance exercise workout can get to limiting limiting muscle glycogen level Want Want to start with adequate muscle glycogen Example study from our lab Interrelationships between muscle glycogen, sarcoplasmic reticulum function, and muscle damage during high intensity exercise Smith, Stevens, Walberg Rankin, Williams GSSI, Reebok ACSM grant Subjects 8 competitive cyclists competitive currently currently cycling > 4X/week 4X/week males ages 18 males, ages 18-30 Peak Peak VO2 = 58 ml/kg•min All All did glycogen depletion ride followed by either hi or low carbohydrate diet for 36 h Cycling Protocol 6060-sec MAX EFFORT intervals 125125-135% VO2peak 3-min recovery recovery Repeated Repeated to FATIGUE (70% initial rpm) Performed Performed 3 times: – Baseline – Performance Trial I (high or low carbohydrate) – Performance Trial II ( “ ) Measures Blood Blood (pre, 15% fatigue, 30% fatigue, 1, 2, 24 h post) Muscle biopsies (pre, 15% and 30% fatigue) Muscle (p # 16 14 12 10 8 6 4 2 0 Total Number of Intervals, 0-30% Fatigue * LC HC ConcludedConcluded- carbohydrate & repeated sprints Carbohydrate Carbohydrate loading enhanced ability to maintain performance in repeated sprints A similar study by another lab (Davis @ similar U South Carolina) showed that acute acute carbohydrate carbohydrate beverage ingestion also delayed fatigue with repeated sprints Overall Conclusions Carbohydrate & athletes Benefit Benefit for most activities longer than 60 minutes ? Single efforts less than 60 min? min? Resistance exercise performance Resistance exercise performance? Not Not likely to help single max effort Probably Probably helps repeated sprint perf. Probably Probably helps team sports performance that includes prolonged running at various intensities Summary of recommendations for carbohydrate Training Training diet 5-10 g/kg (55-70% carb) (55carb) Carbohydrate Carbohydrate loading for endurance events >60 min >60 min High High carbohydrate pre-game meal (lower preglycemic index better?) Carbohydrate Carbohydrate beverage during event (30-60 (30g/hr or ~ 1g/min of< 10% sol’n) sol’n) High High glycemic index carbohydrate ASAP after exercise (1.2 g/kg/min for first 2 h) (1.2 h) Hot topic- train with low topiccarbohydrate? • Get superior muscle enzyme adaptations and train your body to use fat better? • We will discuss this more in Fat lectures This runner comes to you…. CrossCross-country runner, in season – 50 kg, 12% body fat Case study Estimate Estimate energy requirement Performance Performance has dropped off Coach asks for nutrition consult Coach asks for nutrition consult Consult: Consult: – Running 5-15 miles/d 5– Energy intake 2300 kcal/d – Carbohydrate 200 g/kg – Goals: coach wants her to lose 7 pounds as says will improve her pace Calculate Calculate g/kg carbohydrate & % carb Discuss preDiscuss pre-game meal, consumption during training runs, recovery nutrition You You can see how very important carbohydrate is for many athletes thl ...
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This note was uploaded on 03/23/2010 for the course HNFE 4174 taught by Professor Rankin during the Spring '10 term at Virginia Tech.

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