Practical nutrition considerations for athletes
This is an excerpt from Principles and Practice of Resistance Training by Michael Stone,Meg Stone & William Sands.
Several aspects of nutrition beyond the norm are commonly encountered by athletes. The types and amounts of food eaten are important, but when foods are eaten may be just as important. For example, pre- and postevent meals can be of considerable benefit if the appropriate amount, type, and timing of ingestion are taken into account. Athletes (particularly in body weight category sports) are constantly faced with "making weight," and all athletes must pay special attention to fluid balance in order to avoid dehydration and its consequences.
Pre- and Postevent Meals
Athletes can derive both physiological and psychological benefits from a precompetition meal. Under certain conditions, protein intake shortly before training may enhance tissue remodeling and hypertrophy (Volek 2003); protein taken in as a large meal several hours before competition may not have profound physiological benefits but may be psychologically satisfying. A pretraining or precompetition meal high in fat may reduce performance by slowing gastric emptying.
The amount of carbohydrate taken in before an event is an important consideration because of the relationship of carbohydrate to performance. However, some data suggest that consuming relatively large amounts of glucose or sucrose 30 to 60 min before exercise can lead to a rebound depression of blood glucose as a result of an insulin spike in susceptible individuals (Foster, Costill, and Fink 1979). Other studies indicate that a rebound effect will not occur with the ingestion of simple sugars and that glucose ingestion 30 to 60 min preevent can make more glucose available to the muscle during exercise (Gleeson, Maugn, and Greenhaff 1986; Hargreaves et al. 1987). Large amounts of carbohydrate (and protein) ingested as preevent meals typically should be in the form of a drink, especially immediately before or during exercise, as considerable discomfort can occur from the ingestion of a large amount of carbohydrate in the form of food.
During prolonged aerobic exercise (Lamb and Brodowicz 1986) and repeated bouts of anaerobic exercise (Lambert et al. 1991), especially in hot environments, drinks containing glucose or glucose polymers may reduce cardiovascular and thermoregulatory disturbances better than water alone. The "strength" of the solutions should be 4% to 20% carbohydrate, and the drink should be consumed every 15 to 20 min, especially during the final stages of long-term endurance events when blood glucose may be decreasing. However, solutions above 6% may be unsuitable for some types of endurance events as a result of gastric upset or delayed gastric emptying. Although increasing the concentration of carbohydrate in solution will increase absorption, this effect is offset by a decreased gastric emptying. Carbohydrate solutions greater than 20% should not be used because they slow gastric emptying to the point that increased absorption will not compensate for the higher concentrations. Fructose should be avoided during exercise, as it has been associated with gastric upset.
Postevent meals should consist of high carbohydrate content to aid in glycogen restoration. One can maximize glycogen recovery by consuming 1 to 3 g carbohydrate per kilogram of body mass within 2 h and continuing every 2 h following exercise (Friedman, Neufer, and Dohm 1991; Sherman and Wimer 1991). Some evidence indicates that simple carbohydrates ingested during the first 6 h postexercise result in greater glycogen repletion than do complex carbohydrates (Kiens et al. 1990). Additionally, some evidence indicates that glucose more readily promotes muscle glycogen storage and that fructose may more adequately restore liver glycogen (Friedman, Neufer, and Dohm 1991). Although not all studies agree, the addition of protein may enhance glycogen repletion as well as contribute to tissue repair and remodeling, particularly when ingested as an immediate pretraining or recovery drink (Ivy 2001; Volek 2003).
Loss of appetite often accompanies fatigued states and overwork or overtraining. Loss of appetite can result in too little energy and underconsumption of other nutrients (Jaquier 1987). The resulting loss of food energy and nutrients could compound or potentiate overreaching and overtraining, leading to poor performance. For example, alterations were noted in food intake among 16 junior weightlifters during a one-week camp (Stone et al. 1989, 1991b). Many of the athletes reported depressed appetites. Although the percentage of caloric intake for carbohydrate increased slightly, total calories were reduced by approximately 350 kcal as a result of a lower fat intake and simply eating less. Intake of B vitamins decreased over the week. Potentially this trend of fewer calories and lower vitamin intake, if continued, may eventually have contributed to an overtrained state. Therefore one factor that may help to avoid overtraining is adequate nutrition.
Water and Electrolytes
Water is the most plentiful component in the human body (Herbert 1983). Water makes up about 60% of a male's body weight and about 50% of a female's body weight. Of the total body water, about 55% is intracellular, 39% is intercellular, and about 6% is found in the plasma and lymph. Intracellular water functions in providing form and structural support and providing a medium for various biochemical reactions. Extracellular water serves as a means of transport and exchange of biological materials such as nutrients and metabolic by-products like gases, and as a medium for heat exchange. Even small changes in intra- or extracellular water content can result in large functional changes, since biological reactions, thermoregulation, and electrolyte balance are dependent on adequate water.
Dehydration can result in a variety of performance and health problems, even death. Dehydration resulting in the loss of as little as 1% to 2% of body mass, even for short periods of time (i.e., hours), can adversely affect a variety of mental and physiological functions. Mild dehydration (1-2%) can result in loss of performance, including cardiovascular function and performance (Maughn 2003; Saltin and Stenberg 1964), intermittent cycling performance (Walsh et al. 1994), perhaps muscle strength (Schoffstall et al. 2001), and memory processing and cognitive function (Wilson and Morley 2003). Indeed, prolonged mild dehydrated states have been associated with central nervous system damage (Wilson and Morley 2003). Of particular importance is the relationship between hydration state and thermoregulation; dehydration can promote feelings of fatigue, heat exhaustion, and heatstroke. Thus, any level of dehydration prior to and during exercise should be avoided.
During exercise, sweating rates can be affected by a number of factors, including temperature, humidity, and the type of clothing worn. It is not uncommon to lose 2% to 3% of body mass, mostly water, during a typical exercise session, especially in hot environments. When fluid replacement is inadequate, losses of up to 8% of body mass have been reported during very long-term exercise, such as marathon running, or repeated high-intensity exercise such as fall football training (Bowers and Fox 1992; Roy and Irwin 1983). Of note is the observation that thirst often lags behind the need for water (Engell et al. 1987). Thus, fluid should be ingested even though thirst may not yet be recognized by the athlete. Typically 450 to 600 ml (15-20 fl oz) every 30 min should be adequate fluid replacement for long-term exercise, as well as prolonged intermittent high-intensity exercise such as football training.
Hydration of athletes, especially at altitude and in hot environments, is a must (Oppliger and Bartok 2002). While blood measures of hydration are the most accurate, they are invasive and quite expensive. Urinary specific gravity measured by refractometry is relatively easy and is a reasonably accurate indicator of hydration state. Weighing the athlete before and after practice is also valuable for determining rehydration; a pint (at least) per pound of body weight lost should be replaced.
Electrolytes are minerals that have a positive or negative charge, are associated with membrane potentials, and are soluble in body fluids (Herbert 1983). Substantial loss of electrolytes can interfere with a variety of physiological functions, including active and passive transport systems and fluid balance, and can indirectly affect thermoregulation as well as various metabolic functions. Of the electrolytes potentially lost during exercise, largely through sweat, the most important are sodium, potassium, and chloride (Maughn 2000). Sodium and potassium are cations (positive charge), and chloride is an anion (negative charge). Most electrolytes, including these three, are easily obtained in the diet.
Both sodium and potassium are related to blood pressure maintenance and to the development of hypertension. A high sodium intake may increase blood pressure; however, if the potassium intake is 40% of the sodium intake, blood pressure may decrease. The sodium:potassium ratio is a primary factor in reducing hypertension, particularly among sodium-sensitive individuals (Geleijnse, Kok, and Grobbee 2003; Kaplan 1986). A serum sodium:potassium ratio of 0.6 is generally recommended as helpful in reducing the incidence of hypertension.
Electrolytes are usually available in sport drinks, most of which also contain carbohydrate. These sport drinks, used to prevent dehydration, counter losses of electrolytes as a result of sweating and enhance recovery, particularly of glycogen. While electrolytes and some vitamins may be lost in sweat during exercise, losses are not typically large or significant, especially among acclimatized athletes (Herbert 1983). Although the content of sweat is variable, sweat is always hypotonic compared to fluid compartments; thus the net effect of sweating is an increase in osmolality of the plasma (Maughn 2000). Thus, the replacement of electrolytes may be unnecessary. However, although scientists' attitudes were initially skeptical, sport drinks likely offer benefits to athletes, at least under certain conditions. Most sport drinks contain low amounts of sodium (10-25 mmol · L-1), partly to replace lost sodium and partly because of the expectation that sodium may enhance intestinal absorption of fluid (Burke and Read 1993). Additionally, during exercise lasting more than 4 h, such as ultramarathons, low plasma sodium concentrations can result (hyponatremia), especially if low-sodium drinks (water or cola) are ingested along the way (Maughn 2000). Training in hot environments may also result in low sodium concentrations, especially in nonacclimatized or partially acclimatized athletes; this condition usually takes three to five days to develop (McCance 1936; Sohar and Adar 1962), and it is possible that chronic ingestion of a sport drink could offset its development.
It is not unusual to find body mass values of 100 to 160 kg (220-353 lb) in sports such as American football, rugby, and throwing events and in the heavier classes for boxing, judo, powerlifting, and weightlifting. Considerable thought and planning are required for an athlete to achieve these large body masses such that LBM gains are optimized and fat gains are minimized, resulting in a greater potential for superior performance. The planning includes not only physical training but also optimal nutritional strategies. For those athletes contemplating increases in body mass, the following issues should be considered.
Although the goal of gaining weight is to maximize the increase in LBM and minimize fat gains, well-trained athletes will almost always gain some fat (Forbes 1983, 1985; Forsberg, Tesch, and Karlsson 1978), and substantial gains in body mass are almost always accompanied by an increased body fat percentage (Forbes 1985).
Although not all studies agree (Dich et al. 2000), some data suggest that even in diets with the same number of calories (isocaloric), people can gain greater amounts of body fat with a diet that contains relatively more fat calories, especially if they stay with it for a long time (months) (Boissonneault, Elson, and Pariza 1986; Donato and Hegsted 1985; Tsai and Gong 1987). Part of the reason for the greater gain in body fat with a greater dietary fat content may relate to the type of fat ingested. Some evidence indicates that monounsaturated fat may produce less fat gain because of their higher thermic effect compared to that of saturated fats, even in isocaloric diets (Piers et al. 2002). So it would be prudent when one is gaining body mass to keep the fat content under 30% of total calories and to ingest a relatively greater amount of unsaturated fats (70-80% of total fat intake). Keeping the fat content low may be difficult, particularly when the athlete is consuming substantial calories (>5000 kcal · day-1). Additionally, individual differences can affect dietary outcomes. Some evidence indicates that individuals eating different amounts of macronutrients can maintain similar total and percent body fats even with similar energy expenditures (Whitley et al. 1998). Thus, meals should be planned carefully; if difficulty arises (such as large gains in fat), a nutritionist should be consulted.
Special weight gain products purchased over the counter are usually not warranted. Some of these products contain relatively large amounts of fat (>30%) and should be avoided. People can add extra energy to the diet by ingesting extra food; however, this often leads to increased and uncomfortable feelings of fullness, especially if the extra food is eaten in one sitting. If work, school, training schedules, cost, or simply individual preferences preclude the ingestion of extra food, then a supplement is useful. A relatively inexpensive source of protein and carbohydrate (and additional calories) is skim milk. Skim milk can be flavored to taste or mixed with other food and can be used in liquid or powder form. However, among advanced elite athletes, supplementation may be useful in order to promote positive adaptations to hard training (see chapter 7, "Ergogenic Aids").
It is best to increase body mass using a planned diet and specific physical training, particularly weight training, which can enhance gains in LBM. Gains in body mass should be made relatively slowly, at approximately 0.5 to 1.0 kg · week-1 (1-2 lb), as this lower rate of body mass gain has been observed to reduce body fat gains (Birrer 1984). Prolonged weight gain (less than six months) during which large amounts of weight are gained should occur at an even slower rate. During long-term weight gain, the rate of body mass increase should be about 0.25 to 0.5 kg · week-1 (0.5-1.0 lb) to ensure that fat gain is minimized.
Body mass gains and alterations in body composition should be monitored closely, every one to two weeks, by skinfolds or hydrostatic weighing. If the percentage of body fat increases markedly, then the training and diet program should be altered. The authors' observation suggests that high-level athletes (American football players, throwers, and weightlifters) already training with high volumes and intensities typically gain 1% to 3% in body fat for each 10 kg (22 lb) of body mass gained.
Upon retirement, large athletes should be encouraged to lose body mass. Reductions in body mass and fat content can reduce the potential for heart and other degenerative diseases. In the college and professional setting, it would not be unreasonable to make nutritional and training counseling available through the appropriate specialists.
Weight and Fat Loss
Weight loss (or making weight) is not uncommon among sports with stringent body weight limitations (body weight classes) such as boxing, judo, lightweight crew, wrestling, and weightlifting. It is essential to take care in both maintaining and losing body mass; otherwise performance can suffer. Even in sports without body weight classes, such as gymnastics, achieving and maintaining low body weight and body fat are necessary in order to be competitive. Achieving body mass and body fat goals often requires considerable body mass reduction. Athletes (and their coaches) contemplating a reduction in body mass should consider the following issues.
Untrained individuals and beginning athletes can lose body fat (and sometimes body mass) while increasing LBM as a result of caloric restriction and training (Stone et al. 1983). However, it is unlikely that athletes already possessing a low body fat and low percent fat can lose substantial body mass and not lose some LBM as well, especially if caloric restriction is used to enhance body mass loss (Ballor et al. 1988; Walberg et al. 1988). The loss of LBM due to caloric restriction can be reduced through training, particularly resistance training (Ballor et al. 1988), and through use of a high-protein diet during the caloric-restricted period (Walberg et al. 1988). The use of fad diets such as total liquid diets should be discouraged.
The ideal weight for performance is not necessarily the lowest body mass an athlete can maintain. Semistarved or dehydrated athletes do not perform well. Caloric restriction can potentiate depleted energy stores, fatigue, and overtraining (Stone et al. 1991b). Among children and adolescents, some evidence suggests that caloric restriction can reduce adult stature (Smith 1976).
The maximum rate of acceptable loss of body mass appears to be about 1% per week. For most athletes this would be approximately 0.5 to 1.0 kg · week-1 (1-2 lb) and would equal a caloric deficit of about 500 to 1000 kcal · day-1 (Fogelholm et al. 1993). Slower rates of body mass loss are typically more desirable, resulting from a caloric deficit of about 100 to 400 kcal · day-1. Faster rates can potentiate marked loss of LBM, glycogen stores, dehydration, and loss of vitamin and mineral intake and can increase the potential for overtraining (Fogelholm et al. 1993; Walberg-Rankin 2000). Caloric restriction and loss of body mass carried out over more than four weeks, or a total body mass loss of more than 5%, may also alter the micronutrient status of the athlete such that performance could be adversely affected (Fogelholm 1993). It is important to realize that the weight loss needs of very small or very large athletes have not been adequately addressed in the literature.
Body fat may also be too low. A low body fat content in males has been associated with lowered testosterone concentrations and increased incidence of injury (Strauss, Lanese, and Malarky 1985; Vorobyev 1978). The incidence of impact injury and perhaps overuse injury may also be increased as a result of low body fat (Nindl et al. 1996; Wang et al. 2003). Body fat in males should typically not drop below 6% and in females not below 10%.
People can accomplish rapid reductions in body mass with fluid restriction (short-term). The practitioners believe that these rapid reductions enhance performance because much of the LBM acquired at heavier body masses is retained. Although this method of rapid weight loss is widely practiced, it may be accompanied by the following potentially nonbeneficial effects (Walberg-Rankin 2000):
Reduced strength (probably least affected unless weight loss is very rapid) and power
Decreased low- and high-intensity endurance
Lowered plasma volumes
Reduced cardiac function
Impairment of thermal regulation
Decreased renal function
Decreased glycogen concentrations
Loss of electrolytes
Rehydration often takes more than 5 h. Although the practice of dehydration-rehydration is common among weight class sports, the potential positive effects of dehydration-rehydration during subsequent competition may be negated. Observation suggests that the effect of dehydration is often quite negative (Vorobyev 1978; authors' observation), especially with losses of more than 2% body mass. Furthermore, the cumulative effects of repeated bouts of rapid dehydration may also be negative (Vorobyev 1978). Rehydration by artificial means, such as intravenous infusion of fluid, can be dangerous and should be avoided. When making weight it would be prudent to avoid foods that cause water retention (salty foods) and high-fiber foods.
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