Sports Nutrition1

Sports Nutrition1

Melvin H. Williams

Sport, an international phenomenon, is characterized by the pursuit of excellence; and for any given athlete, excellence in sports performance is dependent on the combination of nature (genetics) and nurture (environment). Genetic endowment with physical and mental attributes important to a specific sport is vital to sports success, but so too are common environmental effects such as appropriate training programs and sports nutrition (1).

Sports nutrition has evolved considerably over the course of 50 years and now is considered by many sports nutritionists to have several main objectives:

  • To promote good health

  • To promote adaptations to training

  • To recover quickly after each training session

  • To perform optimally during competition

These objectives include some applications to help optimize performance in specific sports, such as attaining an appropriate body mass and composition, providing appropriate amounts of energy substrate, preventing a nutrient deficiency that may impair performance, and preventing the premature onset of fatigue.

In general, the diet that is optimal for health is also optimal for performance for most athletes. However, in their joint position stand on Nutrition and Athletic Performance, the American Dietetic Association (ADA), Dietitians of Canada (DC), and American College of Sports Medicine (ACSM) (2) indicated that some athletes may benefit from increased intake of specific macronutrients, particularly carbohydrate and protein, whereas some may need specific micronutrients, including vitamins and minerals; others may benefit from specific sports supplements.

This chapter highlights some of the key findings of sports nutrition research with a focus on performance enhancement. The selected readings and references cited at the end of the chapter provide greater detail. The evidence-based ADA/DC/ACSM position stand (2) provides
detailed recommendations for athletes 18 to 40 years of age, whereas other reviews provide recommendations for younger (3) and older (4) athletes. The previous version of this chapter (5) provides details of supplements not covered here. Additionally, for detailed information related to a specific macronutrient or micronutrient discussed in this chapter, please refer to the respective chapter in this text.


The nutrients in the food we eat have three basic functions—to provide energy, regulate metabolism, and promote growth and development. Although all three functions are important to athletes, energy production and energy balance are the essential factors.

Energy production in the muscles provides movement for all sport activities. In brief, muscles contain various forms of energy stores whose contribution to muscle energy production is dependent primarily on the intensity of exercise; the following hierarchy presents muscle energy sources from highest to lowest exercise intensity:

  • Adenosine triphosphate (ATP): Immediate source of energy for high-intensity exercise

  • Phosphocreatine (PCr): Replaces ATP very rapidly during high-intensity anaerobic exercise

  • Glycogen: Replaces ATP rapidly during high-intensity anaerobic exercise and moderately rapidly during endurance aerobic exercise

  • Fatty acids: Replace ATP less rapidly during aerobic endurance exercise

Dietary carbohydrate and dietary fat provide glucose and fatty acids that, respectively, also may enter into muscle energy pathways and help to replenish muscle glycogen and fatty acid energy stores. Dietary protein provides amino acids that may be used as a source of muscle energy, although amino acids are not very important energy sources during exercise. Other dietary nutrients, such as creatine, also may help increase specific muscle energy stores. Energy balance is the key to weight control, and body mass and composition are important considerations for most athletes. Increasing body mass, primarily muscle mass, may enhance performance in a wide variety of sports, such as weightlifting competition, in which strength and power are main determinants of success. Decreasing body mass, primarily fat mass, also may enhance performance in sports, such as distance running, in which economy of motion is important. Discussion of body weight control is beyond the scope of this chapter, but methods used to determine energy requirements, increases muscle mass, and lose excess body fat for enhanced sport performance have been provided in ACSM position stands (2, 6, 7). All ACSM position stands discussed in this chapter may be accessed at


Carbohydrate use rises progressively with increases in exercise intensity and is the most important energy source for high-intensity anaerobic and moderately high- to high-intensity aerobic exercise. Fatigue during anaerobic exercise is associated with adverse effects of muscle cell acidity caused by increased lactic acid production during anaerobic glycolysis, whereas fatigue during prolonged aerobic exercise may be associated with low blood glucose (hypoglycemia), which may impair central nervous system functions, inducing muscular weakness and fatigue. Additionally, low muscle glycogen levels may reduce energy production from both anaerobic and aerobic glycolysis. Thus, adequate carbohydrate intake is an important nutritional concern for both aerobic endurance and highintensity, intermittent sport athletes if it can help maintain optimal blood glucose and muscle glycogen levels (8, 9).

Carbohydrates in the Daily Diet

The slogan “train high and compete high” refers to the concept of training and competing with high carbohydrate intake. A high daily intake of carbohydrate during training helps sustain high levels of training intensity. The ACSM, ADA, and DC (2) note that during times of high physical activity, energy and macronutrient needs, especially carbohydrate, must be met. The carbohydrate recommendation for athletes ranges from 6 to 10 g/kg body weight daily, the amount depending on the athlete’s total daily energy expenditure, type of sport, gender, and environmental conditions. For example, the amount of carbohydrate needed by an athlete exercising to lose weight is quite different than that by one in training to run a marathon. The recommended carbohydrate intake for athletes meets or exceeds the upper level of the acceptable macronutrient distribution range (AMDR) of 45% to 65% of daily energy intake.

In general, athletes should consume healthy carbohydrates, mainly whole grains and rice, legumes, fruits, and vegetables within an overall balanced diet. An excellent model is the OmniHeart (Optimal MacroNutrient Intake) diet based on consumption of healthy carbohydrates, healthy fats, and healthy protein. However, given total daily energy expenditure and increased dietary carbohydrate recommendations for many athletes, such diets may be complemented with some high-glycemic index foods to replenish muscle glycogen.

Carbohydrates after Exercise to Promote Recovery

Athletes may train intensely on a day-to-day basis, or may even train several times daily, and may need to replenish muscle glycogen to sustain such high training loads. Reviews of dietary strategies to promote glycogen synthesis after exercise indicated that supplementing at 30-minute intervals at a rate of 1.2 to 1.5 g of carbohydrate/kg body weight/hour appears to maximize synthesis for a period of 4 to 5 hours after exercise (10). Carbohydrates with a high glycemic index may facilitate muscle glycogen replenishment when consumed immediately after exercise and every 2 hours thereafter.

Carbohydrate Metabolites and Exercise Performance

Several metabolites of carbohydrate have been theorized to possess ergogenic potential. Pyruvate, a three-carbon metabolite of glycolysis, is theorized to accelerate the Krebs cycle or use glucose more efficiently. However, limited research suggests that pyruvate supplementation is not ergogenic (5, 14). Ribose is a five-carbon monosaccharide that comprises the sugar portion of ATP. Supplementation is theorized to increase ATP resynthesis and promote faster recovery and exercise performance. However, reviews and studies (10, 15, 16) indicate that ribose supplementation has no effect on a wide variety of exercise and sport performance tasks.


Fat may be an important energy source during exercise. Although endogenous fat stores cannot produce energy anaerobically, free fatty acids (FFAs) can contribute significantly to muscular energy production via aerobic lipolysis during endurance exercise. FFA oxidation may be derived from intramuscular triglycerides (IMTGs) or delivered to muscles via blood FFAs derived from adipose cell triglycerides or the liver. Endurance exercise training, by enacting multiple mechanisms, enhances the use of fat for energy during aerobic exercise. Endurance athletes are better fat burners.

However, several reviews (17, 18) noted that despite considerable progress, our understanding of how lipid
oxidation is controlled during exercise remains unclear. Research indicates that the rate of lipid oxidation reaches a peak at 50% to 60% of maximal oxygen uptake ([V with dot above]O2max), after which the contribution of lipids decreases both in relative and absolute terms. With exercise greater than 60% [V with dot above]O2max, metabolic byproducts of increased carbohydrate oxidation, among other factors, may impair lipid oxidation. Theoretically, it may be advantageous for endurance athletes to optimize the use of fat as an energy source to spare enough liver and muscle glycogen for the later stages of an aerobic endurance contest.

Fats in the Daily Diet

The ADA/DC/ACSM (2) position stand notes that fat, a source of energy, essential fatty acids, and fat-soluble vitamins, is important in the diets of athletes and recommends that athletes should obtain approximately 20% to 35% of total energy intake from fat, which is the AMDR. The position stand also notes that consuming less than 20% of energy from fat does not benefit performance. As with healthy carbohydrates, diets for athletes should focus on healthy fats, which are promoted in the OmniHeart diet. In general, the goal is to replace saturated fats, sugars, and refined starches with monounsaturated and polyunsaturated fats, such as olive oil, canola oil, and unsalted nuts such as almonds and pecans.

Increased Dietary Fat and Exercise Performance

Several sports nutritionists have challenged the dogma that endurance athletes need high-carbohydrate diets and suggest that endurance performance may benefit from high-fat diets, even one that comprises more than 50% of the daily energy intake as fat (19). Proponents of the high-fat diet suggest that athletes can adapt to high-fat, low-carbohydrate diets and maintain physical endurance capacity; high-fat diets can increase the muscle concentration of triglycerides; and high-fat diets increase use of fat as a fuel during exercise and decrease the use of carbohydrate, leading to enhanced endurance in prolonged aerobic exercise (19). The term “fat loading” has been used to describe both acute (1 to 2 days) and chronic (1 to 2 weeks) dietary techniques theorized to increase IMTG content and fat oxidation during exercise (10). Fat loading has been shown to increase IMTG content and increase fat oxidation during exercise (20), but as noted (5), its ability to enhance exercise performance has not been well documented. Fat-loading practices, either acute or chronic, may increase use of fat during endurance exercise, but do not appear to enhance exercise or sport performance. One study indicated that high-fat diets actually may impair some types of performance, such as sprint cycling stages during a 100-km cycling time trial (21). The ADA/DC/ACSM position stand does not recommend high-fat diets for athletes (2).

Fat Metabolites and Regulators and Exercise Performance

Several different types of fats, fatty acids, and regulators of fat metabolism have been theorized to enhance exercise performance. Omega-3 fatty acids, primarily eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), have been theorized to enhance exercise performance in a variety of ways. As noted (5), omega-3 fatty acid supplementation does not promote muscle anabolism during resistance exercise, and more recent research with α-linolenic fatty acid, another omega-3, also reports minimal effect on muscle mass and strength during resistance training (22). Studies report that EPA and DHA supplementation could increase stroke volume and cardiac output (23) and reduce heart rate and oxygen consumption (24) during submaximal exercise. However, other exercise studies reported no effect of fish oil (EPA and DHA) supplementation on peak oxygen uptake or peak exercise workload (24), glucose or lipid energy metabolism (25), or 10-km time-trial performance in trained cyclists (26). Overall, current research suggests that omega-3 fatty acid supplementation does not enhance sports performance.

Medium-chain triglycerides (MCTs) have been theorized to be ergogenic because of their more rapid absorption into the portal circulation, facilitated entrance into muscle cell mitochondria, and an oxidation rate comparable with exogenous carbohydrate. MCT supplementation, either alone or combined with carbohydrate, has been investigated as a means to enhance endurance exercise performance. However, as noted here (5) and in a subsequent review (10), research indicates that MCT supplementation does not improve, and may impair, endurance exercise performance. Additionally, consuming an MCTcarbohydrate solution provides no additional benefits compared with a carbohydrate solution alone.

Conjugated linoleic acid (CLA) is a collective term for a group of isomers of linoleic acid, one of which is theorized to reduce lipid uptake by adipocytes. CLA supplementation is purported to have several health benefits but has been studied primarily for its potential to decrease body fat. Losing excess fat may be beneficial to some athletes. However, although studies with mice have shown significant effects on body fat reduction, research findings with humans have not been as strong. In two metaanalyses of 18 studies (27, 28), CLA supplementation was shown to produce a very modest loss of body fat, approximately 0.05 kg/week, and a small total increase (<1%) in lean body mass. Studies involving physically active subjects are limited. In one well-designed study, CLA supplementation resulted in minimal changes in body composition and no changes in strength tests in men and women involved in resistance training (29). Investigators indicate that the antiobesity mechanisms of action of CLA are unclear, and its use in humans is controversial (30). Additional research is merited, particularly with athletic subjects.

Phospholipids represent a class of lipids found in most cell membranes that contain a diglyceride (glycerol and two fatty acids), a phosphate group, and another molecule such as choline. Several phospholipid supplements— lecithin and phosphatidylcholine—have been studied for their ergogenic potential. Several older studies suggested that lecithin supplementation could increase strength and power, but the experimental design used was improper. Subsequent well-controlled research reported no ergogenic effects of lecithin supplementation (31). More recently, phosphatidylserine supplementation has been theorized to enhance exercise performance by various means, including direct effects on cell membrane transport and hormonal responses to exercise (32). Current research has emanated from one research laboratory, and several studies suggested that phosphatidylserine supplementation could increase running and cycling time to exhaustion (10). These findings are interesting, but research with phosphatidylserine supplementation and exercise performance is in its preliminary stages and additional research is merited.

Carnitine is synthesized from amino acids in the body. Two forms are produced, with L-carnitine being the most physiologically active. L-Carnitine is present in the muscles to help move fatty acids into the mitochondria for oxidation. Theoretically, increased L-carnitine levels would facilitate fatty acid oxidation and enhance endurance exercise performance. Major reviews relative to the effect of oral L-carnitine supplementation, as well as other forms of carnitine, have been published. The following are some of the key points of these reviews (10, 33).

  • Supplementation increases plasma levels of carnitine but does not appear to increase muscle levels.

  • Supplementation does not appear to increase fat oxidation during exercise.

  • Neither acute nor chronic (6-day) oral supplementation enhances aerobic endurance exercise performance.

  • Supplementation does not induce weight loss in obese individuals and is unlikely to do so in fit athletes.

Nevertheless, one review (33) suggested that elevated muscle carnitine may have some effects beneficial to exercise performance. The problem is finding a practical means by which the typical athlete may increase muscle carnitine content.

In general, various dietary strategies and supplements theorized to increase oxidation of fat during exercise and enhance prolonged aerobic endurance performance have not been shown to be effective (10).


Protein always has been considered to be one of the main staples of an athlete’s diet. Protein is required for a number of metabolic functions important to exercise performance, including promotion of growth and repair of muscle and other tissues and synthesis of hormones and neurotransmitters (10, 34). Both resistance and endurance training exercise induce protein catabolism during exercise, but protein synthesis predominates in the postexercise recovery period and the type of protein synthesized is specific to the type of exercise (10, 35). Such findings have stimulated research to evaluate the effect of protein supplementation on exercise performance.

Protein in the Daily Diet

The recommended dietary allowance (RDA) for protein is based on the body weight of the individual and the amount needed per unit body weight is greater during childhood and adolescence than during adulthood. The adult RDA for protein is 0.8 g/kg body weight. The AMDR for protein is 10% to 35% of daily energy intake.

Whether athletes require more than the RDA for protein is debated. The National Academy of Sciences (36), in establishing the RDA for protein, concluded that in view of the lack of compelling evidence to the contrary, no additional dietary protein is suggested for healthy adults undertaking resistance or endurance exercise. Furthermore, some scientists contend that physically active people probably could manage perfectly adequately on less protein (37). However, the ADA/DC/ACSM position stand (2) notes that recommending protein intakes in excess of the RDA to maintain optimum physical performance is commonly done in practice and cites recommendations of 1.2 to 1.4 g/kg daily for endurance athletes and 1.2 to 1.7 g/kg daily for strength athletes. In another position stand, the International Society of Sports Nutrition (ISSN) recommended that a protein intake of 1.4 to 2.0 g/kg may improve body adaptations to exercise training (38). Some researchers recommend that older individuals, including athletes, may help prevent the sarcopenia of aging by consuming approximately 25 to 30 g of highquality protein at each meal (39), which over the course of the day will exceed the protein RDA.

Although these viewpoints are divergent, the available scientific data suggest it may be prudent for athletes, particularly those in weight-control sports who may be at risk for protein insufficiency, to consume more protein than the RDA as recommended by the ADA/DC/ACSM and ISSN. Moreover, meeting these recommendations may be achieved by consuming natural food sources. For example, 10% of energy intake from protein provides 75 g of protein, or 1.0 g/kg, to a 75-kg athlete consuming 3000 kcal/ day. Increasing the percentage of protein intake to 15% or 20% provides 1.5 and 2.0 g/kg, respectively, meeting the amounts recommended by the ADA/DC/ACSM (2) and ISSN (38) and staying well within the AMDR recommendation of 10% to 35% of daily energy derived from protein.

As with healthy carbohydrates and healthy fats, diets for athletes should be composed of healthy protein foods. The OmniHeart diet may contain 15% to 25% of energy from protein. Animal sources provide high-quality protein
but should be reduced in fat content, such as lean meat, fish, and poultry; fat-free and low-fat milk and dairy products; whole and high-protein grains (e.g., bulgur wheat, millet); and legumes, nuts, and seeds. Combining animal and plant proteins in one meal, such as milk and cereal or stir-fry vegetables and meat, increases the protein quality of the meal.

Protein Supplementation and Postexercise Recovery

Increased protein before, during, and after exercise has been studied as a means to facilitate recovery from exercise, promote muscle synthesis, and enhance both strength and endurance exercise performance. In most studies, protein supplements, such as whey protein, colostrum, or protein hydrolysate (a high-protein dietary supplement containing a solution of amino acids and peptides prepared from protein by hydrolysis), were added to the diet. In general, protein supplements contained all the essential amino acids. Reviews by several experts have indicated that the difference in anabolic response between preexercise and postexercise ingestion of protein is not apparent, and it is uncertain whether ingesting amino acids immediately before exercise further enhances the muscle protein buildup associated with protein intake during recovery (10). In general, research has shown that consuming protein supplements with all essential amino acids during the first few hours of recovery from heavy resistance exercise produces a transient, net positive increase in muscle protein balance (10).

Many studies also combined protein with carbohydrate, and the general recommendation is a carbohydrate-toprotein ratio of approximately 3 to 4 g of carbohydrate for each gram of protein, preferably in a highly digestible liquid form. Research from one prominent group (40) reported that ingestion of a protein/carbohydrate supplement increased markers of protein synthesis during recovery from aerobic exercise. However, one expert indicated that if adequate protein is available, there is no need for carbohydrates to promote muscle protein synthesis and also noted that because resistance exercise uses muscle glycogen, the carbohydrate could help replenish muscle glycogen (41).

In general, although consumption of adequate protein or protein/carbohydrate preparations during exercise training may provide a milieu conducive to muscle protein anabolism, some have contended that research is insufficient to support an ergogenic effect of such preparations on resistance or aerobic endurance exercise performance beyond that associated with training alone (5, 42). However, some research findings, particularly with whey and colostrum protein supplements, have revealed mixed but generally positive effects relative to the ergogenic potential for whey supplementation to resistancetrained individuals. Small gains in strength and lean body mass have been reported, but additional research is merited (10).

Jul 27, 2016 | Posted by in PUBLIC HEALTH AND EPIDEMIOLOGY | Comments Off on Sports Nutrition1
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