edited bv: MICHAEL R. S L A B A U ~ H
HELEN J. JAMES Weber State College Ogden, Utah 84408
Nutrition (Diet) and Athletics David R. Lineback Department of Food Science, North Carolina State University, Raleigh, NC 27650 In recent vears. there has been increasine interest and emphasis o n the relationship between diet7nutrition and athletic nerformance. T o a laree extent. this is due to the emphasi; placed on winning. with the small diff6:rt:nces in athlettc ahilitv betwren manv nari(,nal- and world-classarhIt.tt.s, individuals seek every assi~tanceto gnin a competitive rdre. Thus. if a winning athlete has a ~artic~tlill d ~ eor t dirtan/ adjunct that helshe uses, others wilicopy it and seek to improve on it, so that they, too, may win. Such attitudes now pervade all levels of competition from junior high school to the olympics. I t includes individuals involved in physical fitness programs, many of whom also have weight problems. When speaking of nutrition and athletics, most people really mean diet and athletics or physical fitness. Nutrition is concerned with the biochemical and physiological processes involved in prowth. maintenance. and reoair of livine" orean" isms. Normally only biochemists, nutritionists, and physiologists are interested in such a definition. Most people are instead interested in what they can eat to give them the "comnetitive edee" in a oarticular snort or to maintain ~hvsical ktness, tharis, theyare only co&rned with the eff&t df diet on physical performance.
Nutritional Requirements The nutritional requirements of an athlete are not significantly different from those of anyone else, except for the greater energy requirement ("calories" I ) due to-increased energy expenditure through training and competition. There is little or no objective evidence that athletic performance can be improved by modifying a basically sound, nutritious diet. The diet of an athlete, like that of any healthy individual,
Plannlng for Athletes-( 1 ) Table 1. Prlnclples of Nulrnional -.. Prcwde the athlete wth necessary qwntitles of energy s.ff c en1 lo meet the expendituresof physical activity
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Adhere to me principles of balanced nutrition according to the kind of sport and physical demand.
Choose adeousle farms of nuhition /food oroduch. nutrients. end their comolnal oni and nvrnoer of tewmgs I3 61 o.rmg the !,mea1 l e n s ve ua nmg ana precornpet~tmonand campet tlon per,ods Use dietary factors for rapid weight reduction to bring the athlete to a
specific bcdy weight. Apply individualized nutrition based on the morphological,physiological. and metabolic characteristics of the athlete and hidher tastes and eating habits.
should he balanced in all nutrients, of sufficient quantity to maintain normal body weight and composed of foods that the individual enjoys. Such a diet does not need to be supplemented with vitamins, minerals, or "fad" foods. Unfortunately, many individuals, including athletes, do not consume sound diets and, as a result, their performance may be adversely affected. These individuals will henefit from vitamin and mineral supplements because of the insufficiency of their diets. I t is well known that food has significance beyond the mere provision of nutrients. For this reason, i t is difficult to know whether an athlete receives psychological henefit from certain foods. Rogozkin ( 1 ) has listed five main principles (Table 1) for creatine nutritional d a n s for athletes. These balance the individuai's requirements for enegy ("calories") with selection information presented might be used directly in class, posted on bulletin boards, or otherwise used la stimulate student involvement in activitiesrelated to chemistry. Contributions should be sent to the feahae editors. The
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The calorie of nutrition is the amount of heat required to raise 1 kg of water 1%; it is equivalent to the kilocalwie(kcal) of thermodynamics, which is the unit used here.
536
Journal of Chemical Education
Table 2.
Recreational Energy Expendlture (2)
Activity
kcallmin
Playing Bridge (sitting) Walking (level. 3 mph) Canoeing (4 mph) Playing Volleyball Playing with children Cycling (13 mph) Golfing Practicing Archery Dancing Swimming Playing Tennis Playing Touch foolball Playing Sqvash Cross-countryskiing Climbing Runnina HO mob\
1.5-2 3-5 3-7 3-10 3.5-10 4-11 5 5 5-7 5-10 7-10 7-10 10-12 10-15 11-12 18-20
of foods and frequency of eating in a halanced diet designed for that individual. The starting point is the amount of energy required by the athlete daily. In a sense, an athlete is like an engine: fuel intake should equal energy output. This is particularly true of competitive athletes, since these individuals normallv desire to maintain bodv" weiebt. " . rather than to lose or gain weight. Tahle 2 illustrates the amounts of enerev exoended in different activities. Several common recre&onal sports have relatively low energy expenditures. Many people have difficulty relating energy expenditure per unit time to the caloric value of a familiar food. Table 3 iists amounts of activities calorically approximately equal to some common foods. To maintain hody. weight, . enerm . . intake must equal energy expenditure. There is not complete agreement on the proper distribution of major nutrients (protein, fat, carbohydrate) in the diet of an athlete. While there are differences in the amounts of protein, fat, and carhohydrate recommended by different investigators, the variation is not great. Current evidence indicates that a balanced diet containing 10-20% motein. 3035% fat, and 5%55% carbohydrate is aiequate fo; athletes as well as other healthy individuals. A common misconception is that the protein content of the athlete's diet should be elevated to facilitate buildinp. muscle mass in soorts reauirine such hulk. Muscle mass is ikreased by exercising the && not by altering the protein content of the diet. Daily caloric intakes for athletes can he estimated by adding the energy expenditure during training or competition to the basal m&bo;ism, the energ):required to maiitain the vital functions of the individual at rest. The hasal metabolic rate (BMR) is about 1kcaVkg hody weightlh for a man or about 1680 kcallday for a 70 kg man (4). It is about 0.9 kcalkg body weightlh for women. The BMR accounts for over half of the total energy required for persons doing mild activity hut is a smaller percentage for an active athlete. Thus, the total daily energy requirements are governed by the intensity of the athletic effort and its duration and by the hasal metabolic needs of that individual. Energy Use
In order for muscles to contract (work) durine athletic competition. the mnscle cells must be supplied with eirergy. T h e n ~ a i nenergy source of muscle is bloud glucose and fatty acids. These are con.rwtt.d to acetyl-SCoA which enters the d r i r arid cvrle in which it it oxidized, using- oxvren - - from the bloodstream, to form carbon dioxide. The energy generated during the oxidation is conserved as reducing equivalents (NADH H+ and M H z ) from reduction of the coenzymes NAD+ and FAD. The energy is released as adenosine triphosphate (ATP) by reoxidation of the reduced coenzymes
+
Table 3.
Approximate Equlvalence of Food Intake and Energy output (3) Minutes of Minutes of Skating at 11 Minutes of Walking at 3% mph or Running a1 5% mph or Cycling Recreational mph or Cycling kcai at 8 mph Swimmins at 13 moh
Food Apple, large Beer (6 oz.) Cola beverage (8 m.) Cheddar cheese (1
m.) Glazed cake-type doughnut (average) Ice cream, 12% fat ('13 CUP) Malted milk shake (8 OZ. milk) Pancake (4 in.), syrup Apple pie ('16 of 9 in.) Loin pork chop (3% OL.)
Hamburger on bun, burger sauce Sirloin steak (10 02. cooked), including
Table 4.
Intensity of Effort and Proportion of Energy Supplied by Carbohydrates (5) Mild
Oxygen uptake (02llmin) % VO*, (measure of work intensity Relative utilization of carbohvdrates 151
.
Relative Intensity MDderate
1.2 29
2.2 53
55.6
65.9
Table 5. Duration of Effort (at,about 60-65% V,, , . , )and Proportion of Energy Supplied by Carbohydrates and Lipids (5)
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Dwalion of Effort (min)
% 01 Energy Supplied by Carbohydrates
Lipids
0- 30 30- 60 120-150 210-240
71 66 47 40
29 34 53 60
by enzymes of the respiratory chain with ultimate formation of water. Thus, the potential energy present in glucose and fatty acids is used to produce ATP with the concomitant production of carbon dioxide and water. The fuel used hv the body to Dower muscular work is adenosine triphosphate (ATF).ATP can he generated from stored carbohydrate (glycogen) or fat (triglycerides). In addition, small amounts of creatine phosphate are also stored in the muscle. For events of short duration (10-20 s), most of the energy is supplied by creatine phosphate. The ATP present in muscles a t rest is too rapidly depleted to act as a reservoir. When the creatine phosphate is used up, high intensity work is no longer possible. However, recovery is rapid, occurring in 2-5 min. Fur events of longer duration, carbohydrate and fat are broken down to produce ATP. This is normally referred to as burning a mixture of fat and carbohydrate. The relative amount of each component in the mixture is determined hv the intensity and the duration of the event, the individoafs total work capaoty or maximal oxygen uptake (Vo:,,,J, diet. and pnasihly genetic heritayt. For m ~ l dt u modtrdte actl\,lty Volume 61 Number 6 June 1964
537
Table 6.
Glycogen Content of Muscle and Maxlmum Work Tlme wlth Various Dietary Manipulations ( 6 )
Diet Normal (18% Protein, 34% Fat. 48% Carbohydrate) HighFat. High-Protein (54% Protein. 46% Fat) High-Carbohydrate (18% Protein. 82% Carbohydrate)
Glycogen Content of Muscle before Performance (g1100 g Wet Muscle)
Maximum Wak Timee (min.)
1.75
114
0.63
57
3.51
167
Table 7.
Source of Fah. Proteins, and Carbohydrates
Phase I, Days 7-4 Before Event
Phase 11. Days 3-1 Before Event
Meat. Fish. Pouliry. Eggs. Cheese Breads and Cereals
12-18 02. 900-1,350 kcal 4 servings 280 kcai 2 servings 50 kca 2 servings 80 kcal 4-12 Tbsp. 540-1.620 kcal 2 servings 300 kca 1 or 2 servings, unsweetened 400 kcal Ncn-sweeteneds unlimited 0 kcal 8 or more servings 0 kcal 2.550-4,080
6-8 az. 450-600 kcal 8-16 servings 560-1,120 kcal 4 servings 100 kcal 4 servings 180 kcal 2-4 Tbsp. 270-540 kcai 2 servings 300 kcal 2 servings. sweetened 800 kcal Sweetened, unlimited to kcal level 0-360 kcal 8 or more servings 0 kca 2.640-3.980
Vegetables Frull~ and Juices Fats and Oils
* T i m a workload of 75% of maxlmal oxygen uptake could be tolerated (nlne Subjedsl.
Milk (whole)
fat is the primary fuel for muscle activity. (20-30% Vop As the intensity increases to about 70% Vo,,,, the amount of oxveen available to the working muscle becomes less and the f&i supply switch- to more intensive use of carbohydrate (Table 4). I.ess oxvren is required to metabolize carbohvdrate than fat. If activity is sustained a t a high level, the "se of carbohydrate as a fuel is greatly increased. However, the body stores only a limited amount of carhohydrate, which can become depleted during strenuous competition or exertion. As the length of the event increases, the-proportion of fat used as a primary fuel also increases (Table 5). To say that the body uses-eitherfat or carbohydrate is misleading, since a mixture of the two is always used. However, the relative amount of the two being used changes during the duration of an athletic event. Few athletes are capable of prolonged performance a t most marathoners operate a t 35-5595 Vo,.,, 70% Voz The body stores much more fat than carbohydrate; i.e., ap~roximatelv100.000 kcal as fat in an averaae non-obese man benus about 2,& kcal as carbohydrate (glycogen plus glucose circulating in the blood). Thus, even a lean individual contains far more fat than carbohydrate. As a rough estimate, running uses about 100 kcallmi. Therefore, it is possihle to deplete most of the glycogen from muscle during a long-duration event such as a marathon. Some believe that this mav be the phenomenon responsible for the "wall," which so many marathoners have experienced a t 18-20 mi. However, many world-class runners apparently do not experience the "wall!' As with most biological phenomena, the explanation is probably not this simple.
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Loading Since the breakdown of carbohydrate produces 10%more energy per liter of oxygen (5 kcal) than does fat (4.6 kcal), endurance might he expected to improve if more carhohydrate were available for metabolism in a ~roloneedathletic event. such as marathoning, cross-country skiing, or long-distance swimming. Studies have shown that the size of the glycogen stores is a limiting factor in activities of high intensity or long duration. Astrand (6)studied the glycogen content of muscle and maximum work time for subjects on a normal diet, a high-protein diet, and a high-carbohydrate diet. As shown in Table 6, there were differences in muscle glycogen content and maximum work time on the three diets. On a high-fat, highprotein diet, the glycogen content of muscle was reduced and the amount of time that the subject could work a t 75% of maximum oxygen uptake was reduced to half of that which the subject could do on the normal diet. However, when a hieh-carbohvdrate diet was used. the -. elvcoeen content of " m&le was 2oubled and the work time was increased approximately 50%.This was attributed to the increased amount of carbohydrate available in the muscle for use during exercise. Similar work had been reoorted earlier from other lahoratoCarbohydrate
These observations became the basis for the practice known as carbohydrate loading (glycogen packing). In this procedure, 538
Journal of Chemical Education
Dally Food Plan for Carbohydrate Loading ( 7 )
Des~erls
Beverages
Water Total kcal
Avom artiliciall~ sweetened.
the athlete does exhausting exercise one week prior to the competitive event. For a marathoner, this could he a 20-mi run. This results in depletion of the glycogen stored in the muscles. Following this, the individual consumes a diet low in carhohvdrate. mhstlv nrotein and fat. for about three davs. Initially, k a n y tried todeplete completely their diets of carhohvdrate. There is considerable daneer in doine" this.. since " renal damage may occur due to elimination of metabolites from a hieh-orotein. hieh-fat diet. The diet should include some cargohidrate (at Teast 100 g daily) to prevent severe ketosis from occurring. An example of a possible diet is shown in Table 7. Note that Phase I reduces the amounts of carbohydrate in the diet. This is known as the depletion phase and further ensures that glycogen reserves in the muscles are depleted. In some individuals, irritability, fatigue, nausea, nervousness, and similar symptoms may be noted during this phase of the carbohydrate loading diet. During this period, the athlete continues to perform tbe usual daily workout although endurance will decrease markedly. The second phsse of the diet begins about three days before the competitive event and features a diet that is high in carhohvdrates with the amounts of fats and nrotein beine decreased. Note that the diet shown in b able? calls for the two nhases to he annroximatelv isocaloric. Initiallv. manv indibiduals did not bo this andundesirable weight ;hang& also occurred. Since annroximatelv three mams of water are hound .. for each gram of glycogen scored, an increase in weight can be expected. Some athletes believe that this additional weight makes them feel sluggish. Huwever, the bound water ran also be beneficial in drlaying drhydration. During phase 11, the use of carhohydrace-rich ioods is increased signiiicantly. This is a diet that many enjoy since they are able to eat the sweet foods desired but denied on a normal diet. I t makes little difference whether the carhohydrate is simple or complex since elvcoeen is formed and stored in muscle from either source (8).Thus, one can consume candies and sweetened drinks. as well as foods hieh in starch content. The reason for the depletion phase preceding this packing phase is that a elvcoeen-deoleted muscle svnthesizes more -elvcoeen than -. " does a muscle containing glycogen. Using this diet, one can increase the elvcoeen content of muscle bv two- to threefold. Training shouid not be continued duringphase I1 since glycogen will be used during the exercise. The carbohydrate-loading diet is not without danger. Cases
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of renal damage have been reported and at least one case of chest ~ a i n has s occurred durine ohase 11. This is not entirelv unexpected. An analogy may G m a d e to a chemical equilibrium. By increasing the concentration of a reactant (carbohydrate), one tries to shift the reaction in favor of a product (glycogen). However, the body is not a simple chemical equilibrium. Many complex chemical equilibria are involved in metabolism, and the effects of changing the substrate (reactant) concentrations are not known. Carbohydrate loading should be used, judiciously, for events lasting more than one hour. While there may be limited benefit for events of shorter duration, they are not sufficient to warrant use of the glycogen-packing regime. It should also be limited to not more than three or four times per year. There is still only minimal scientific evidence to validate the effectiveness of carbohydrate loading. Work already cited indicates that increased endurance is associated with increased glycogen storage. Work is now being done on this topic and reports are beginning to appear in the literature indicating that this procedure may be effective for some athletes. Its effectiveness cannot be generalized, though, until more extensive research is completed and reported. This examole of an attemot to modifv diet in an effort to increase athlekc performanceis perhaps the only one that has anv scientific evidence suooortine its use. Other diets or diet& modifications are &ed testimonials by the individuals involved and have little or no scientific validation. Even carbohydrate loading has a more anecdotal than objective basis supporting its effectiveness. Myths and Fallacies There are several areas which involve false information, misinterpretations, fallacy, or myth regarding food and athletic performance. Some of these will be treated briefly with statements indicating our current understanding of the matter. Fallacy: Athletes should not consume fluids during eompetition. Truth: Athletes should consume fluid before, during, and after competition (exercise).This will enable the individual to delay the onset and severity of dehydration. Consumption of small amounts of fluid will not cause the individual to become "water-logged." It is recommended that athletes consume 400-500 ml of fluid approximately 1530 min before competition (exercise) and then consume 100-200 ml ever" 10-20 min thwughout the event. An individual cannot depeniupon hisher perceptiun uf the degree of thirst tu he an accurate ind~catoruf hydrationldehydration. Maintenance of sufficientfluid in the hody is necessanj for effective functioning of the thermoregulatian system Fallacy: Athletes should replace salt lost during competition and electrolyte supplements are an effective way to do this. Truth: Athletes do not normally need to consume electrolyte (salt) supplementsand should do so only upon recommendation of their team physician. Hypotonic solutions are most rapidly absorbed. The most effective fluid touse is cool (cold)water. It is most rapidly absorbed from the stomach. If the individual prefersto use a flavored drink, fruit juice diluted two- to threefold with water will suffice. Drinks which are more concentrated \isotonic or hypwtmic~,including wme elwtrdyte supplements, delay gastric emptying and in~rmvethe likelihwd of intestinal disturbance. Concentrated solutions (hypertonic) can cause gastric distress by drawing water into the intestinal tract (9). The idea that the athlete must he concerned about replacement of electrolytes lost through perspiration has been overemphasized. It is true that electrolytes lost during exercise/ cornnetition must ultimatelv ,he reolaeed. but mast individuals can do rhiz through one or two normal meals aiter the athletic evmt. 1.nlrss very large amount* of perspiration nre lost ( e l O D ; or mure uf hody weight),the replacement uf fluid lws ia more ~
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cr~tiralthan replacement ofelectrolytrs.l'he useofsalt tablets is not warranted and the use of electrolytesupplements isseldum required. Fluid and electrolyte loss usually can he replaced by consuming water before, during, and after the event coupled with the consumption of normal foods. Fallacy: Products such as bee pollen, brewer's yeast, vitamin E, ascorbic acid (vitamin C), lecithin, honey, wheat germ, wheat germ oil, and others too numerous to list can enhance athletic performance. Truth: Many such products have been touted as having particular or unique ergogenie (work-enhancing)value. There is no evidence that these are of any practical use to an athlete consumine a balanced. nutritious diet. nor is there evidence that tbev have or oerformanee-enhsneine . ~.-nnv -~~ , nnione work-oroducine ~-~~ " power. As mentioned earlier, however, the psychological aspects of foods cannot be separated from their objective nutritional value. Thus, if athletes believe that one of these aids enhances their athletic performance,it may do so even though this cannot he objectively validated in a larger group of individuals. Most of the evidence surrounding these dietary adjuncts is anecdotal.
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Follac) Ncoholtc brvemges are useful to athletes as a source of ealurrei, muscle relaxants, or ergogenlc aids. Truth: Beer, wine, and other alcoholic beverages are not recommended for use hv athletes and do not enhance comoetitive perfirrmmce. While thew twerages are a ready source oicalories, they affect the central nervom sbdtern and also act as diuretics, t ~ n hof which are counterproductive to an atnlete's best effort Fallacy: Athletes require vitamin and mineral supplementsfor optimum performance and training. Truth: There is no objective evidence that athletes need mineral or vitamin supplements when a balanced, nutritious diet is consumed. Controlled studies using such supplementation have not demonstrated physical benefits to athletic performance. Scientific evidence does not validate the use of any special diet by an athlete. An athlete should consume a diet similar to that recommended for the average individual--one that is halanced, nutritious, adequate in calories to maintain weight, and composed of foods the individual enjoys. The Amrrican Dietetic Association has issued an excellent statement on nutrition and ohvsical fitness ( 1 0 ) .The American Colleee of Sports ~ e d i c h e h a established s position statement o n t h e recommended auantitv and aualitv - .of exercise for develonine . and maintaining physical fitness (11).
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Literature Cited
York, 1970. p. 439. (31 "Shaping Up for the l o n g Run,"CPC International, Coventw,CT. 1978. 14) General Milk Nutrition Deoartment."Enerw for Swrt." General Mills. he.. MinTechnical Assistance Co, Lfd.. 1W1 Lsusanne, Switzerland, 1980. (6) Aalrsnd. P.O.,Nulr. Today. 3 IMarIAprl.9 (1968). (7) Forgac, M. T., J. Amer DistalicAssor.,75,42(1979). (81 Costill. 0. L.,Sharmsn,W. M., Fink, W.J., Msrosh. C.. Witten, M.,andMiller, J. M., Arne,. J. Clin Nutr.34.1831 (1981)
Suggested Reading Costill,D., "Sports Nutrition: ThcRoleofCarbohydrMs," 'NUN.New, 41IlI. l(1976). Hanky. D. F., Jr., "Athletic Training and How Diet AffDCtp It," N u t r Todny. 14161, 5
,,wm \.".",. Hanky. D. F., '"Basic Diet Guidance for Athletes" (editorisll, Nulr Today, 1416), 22
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ilP79, , . ,
Nstianal Dairy Council. "Nutrition and Human P8rformance:'Doiry
CouncilDigesf. 51,
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Buskirk, E. R., "Some Nutritional Considmations in the Conditioning of Athletes: A m . Reu. N u l r , 1,319(1981).
Volume 61
Number 6
June 1984
539
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