Research Review By Christopher Howard©

Date Posted:

October 2009

Study Title:

Nutrition & Athletic Performance
A joint position statement from the American College of Sports Medicine, American Dietetic Association and the Dieticians of Canada

Authors:

American College of Sports Medicine: Nancy R. Rodriguez (University of Connecticut); American Dietetic Association: Nancy M. DiMarco (Texas Woman’s University); Dietitians of Canada: Susie Langley

Publication Information:

Medicine & Science in Sports & Exercise 2009; Special Communication: 709-731.

General Overview:

  • Athletes need to consume adequate energy during training to maintain body weight and support performance.
  • Body weight and composition should not be the only the only factors considered in potential for athletic performance. If weight, and more specifically fat loss is a concern, the offseason training program and should involve a sports dietitian.
  • Carbodyhdrate recommendations for athletes range from 6-10grams per kilogram of body weight per day. Carbohydrates are important for maintaining blood glucose during exercise and replacing muscle glycogen.
  • Protein requirements range from 1.2 to 1.7 grams per kilogram of body weight per day, which can generally be met through diet alone.
  • Fat intake recommendations range from 20-35% of total energy intake. Fats are important sources of energy, fat-soluble vitamins, and essential fatty acids.
  • Micronutrient deficiencies are a concern for athletes who restrict energy intake or use severe weight-loss practices.
  • Dehydration is an important factor in decreased exercise performance, thus making adequate fluid intake before, during, and after exercise extremely important. Current recommendations require approximately 16-24 oz of fluid for every pound of body weight lost during exercise.
  • Before exercise, goals include: maintaining hydration, maintaining and maximizing blood glucose and most importantly, minimizing gastrointestinal stress by eating meals low in fat and fiber.
  • During exercise it is important to replace fluid losses and provide carbohydrates (30-60 grams per hour) to maintain blood glucose levels.
  • After exercise it is important to provide adequate fluids, electrolytes, energy and carbohydrates to replace muscle glycogen. Protein consumption during this time period will assist in building and repair of muscle tissue.
  • In general, vitamin and mineral supplements are not required if adequate energy is consumed.
  • Ergogenic aids should be used only after careful evaluation of safety, efficacy, potency, and legality.
  • Vegetarian athletes should be aware of the risks of low energy, protein, fat, iron, calcium, vitamin D, riboflavin, zinc, and vitamin B12 intakes.

Energy Metabolism:

Time for a little biochemistry review…Energy expenditure must equal energy intake to achieve energy balance. There are three energy systems used during exercise: the phosphagen system, glycolytic system, and the oxidative system. The phosphagen system lasts only seconds, while the glycolytic system can provide energy for tasks lasting 1 to 3 minutes.

Any events lasting longer than 2-3 minutes will be fueled by the oxidative pathway. Adenosine Triphosphate (ATP) and creatine phosphate provide energy for the phosphagen system, while muscle glycogen and glucose provide energy for the anaerobic glycolytic system. The oxidative system is fueled by muscle and liver glycogen, as well as intramuscular, blood, and adipose tissue triglycerides.

As oxygen becomes more available to working muscle, the body switches from primarily anaerobic (phosphagen and glycolytic) metabolism to aerobic (oxidative) metabolism. It is important to note that as the intensity of exercise decreases, there is a greater reliance on free fatty acid oxidation for energy production. In addition, as a result of aerobic training, carbohydrate usage decreases and energy derived from fat increases.

A trained individual will also use a greater percentage of fat than an untrained individual at the same workload.

Energy Requirements:

Energy balance occurs when energy intake (the sum of energy from foods, fluids, and supplement products) equals energy expenditure (sum of energy expended as basal metabolic rate [BMR], the thermic effect of food, the thermic effect of activity [TEA], which is the energy expended in planned physical activity, and non-exercise activity thermogenesis).

Energy expenditure for different types of exercise is dependent on the duration, frequency, and intensity of the exercise, the sex of the athlete, and prior nutritional status in addition to heredity, age, body size, and fat free mass (FFM). The more energy used in activity, the more calories needed to achieve energy balance.

Inadequate energy intake compromises performance and negates the benefits of training. With limited energy intake, fat and lean tissue will be used for fuel by the body resulting in a loss of lean tissue. The concern here is that loss of strength and endurance, as well as compromised immune, endocrine, and musculoskeletal function can result.

Most facilities are not equipped to determine total energy expenditure. Therefore, predictive equations are often used to estimate BMR or RMR. The two most commonly used prediction equations are the Cunningham equation (1980) and the Harris–Benedict equation. The Cunningham equation requires knowledge of total lean body mass, therefore the Harris-Benedict equation is most commonly employed by sports dietitians.

Body Composition:

Body composition and body weight are important factors that contribute to optimal exercise performance. However, athletic performance cannot accurately be predicted based on this information. Individualized assessment of an athlete’s body composition and body weight (or body image) may be advantageous for the improvement of athletic performance. However, an optimal competitive body weight and percentage of body fat should be determined when an athlete is healthy and achieving optimal performance.

There are three levels of assessment techniques used to assess body composition. Level 1 is a direct assessment based on analysis of cadavers. This technique is obviously not used in a laboratory or clinical setting. Level II assessments include hydrodensitometry, dual-energy x-ray absorptiometry (DEXA), and air displacement plethysmography. Level III techniques include skinfold measurement and bioelectrical impedance analysis (BIA).

Sports dietitians most commonly employ skinfold measurements and bioelectrical impedance analysis. Body fat percentage in athletes varies depending on the gender of the athlete and the sport, among other factors. The estimated minimal level of body fat compatible with health is 5% for males and 12% for females; however, optimal body fat percentages for an individual athlete may be much higher than these minimums and should be determined on an individual basis.

Macronutrient Requirements for Exercise:

Carbohydrate: Although high-carbohydrate diets (more than 60% of energy intake) have been advocated in the past, caution is recommended in using specific proportions as a basis for meal plans for athletes. Instead, it is better to recommend carbohydrate levels based on a grams per kilogram of body weight per day value (see Background Information above).

Protein: The current recommended dietary allowance (RDA) is 0.8 grams per kilogram of body weight and the acceptable macronutrient distribution range (AMDR) for protein intake for adults older than 18 yr is 10%–35% of total calories. This value does not reflect on the increased needs of those who are active due to the lack of a strong body of evidence indicating additional dietary protein requirements by active adults. Sports dietitians do, however, commonly recommend values higher than this in practice.

It is also important to include the fact that it is recommended that endurance athletes consume 1.2 to 1.4 grams per kilogram body weight per day. In addition, it is important for endurance athletes to consume adequate carbohydrate so that protein is spared for protein synthesis and not used as an energy source. It is suggested that strength and power athletes may require from 1.2 to 1.7 grams per kilogram of body weight per day.

Because protein or amino acid supplementation has not been shown to positively impact athletic performance recommendations regarding protein supplementation are directed primarily at optimizing the training response to and the recovery period after exercise.

Fat: The acceptable macronutrient distribution range (AMDR) for fat is 20%–35% of energy intake. The Dietary Guidelines for Americans and Eating Well with Canada’s Food Guide make recommendations that the proportion of energy from fatty acids be 10% saturated, 10% polyunsaturated, 10% monounsaturated, and include sources of essential fatty acids.

The Vegetarian Athlete:
Some vegetarian athletes may require additional protein intake to meet requirements, although most meet or exceed requirements. Protein quality is an issue for individuals that avoid all animal products, as protein quality of plant-based diets is generally lower. Current recommendations for vegetarian athletes are 1.3 to 1.8 grams of protein per kilogram of body weight per day. In addition, vegetarian athletes may be at risk for low intakes of energy, fat, vitamins B12, riboflavin, and D, calcium, iron, and zinc.

Vitamins and Minerals:

Greater intakes of micronutrients may be required to cover increased needs for building, repair, and maintenance of lean body mass in athletes. Athletes at greatest risk for poor micronutrient status are those who restrict energy intake, participate in severe weight loss tactics, eliminate a particular food group, or those who consume an unbalanced diet. The major vitamins and minerals will be discussed individually below:

B Vitamins (Thiamin, Riboflavin, Niacin, Vitamin B6, Pantothenic Acid, Biotin, Folate, Vitamin B12):
The B-complex vitamins have two major functions directly related to exercise. Thiamin, riboflavin, niacin, pyridoxine, pantothenic acid, and biotin are involved in energy production. Folate and vitamin B12 are required for the production of red blood cells, protein synthesis, and in tissue repair and maintenance. Severe deficiency of vitamin B12 and/or folate may result in anemia and thus decreased endurance performance.

Vitamin D:
Vitamin D is required for adequate calcium absorption, regulation of serum calcium and phosphorus levels, promotion of bone health and in development and homeostasis of the nervous and muscular systems. Athletes who live at northern latitudes or who train primarily indoors throughout the year are at risk for poor vitamin D status. It is suggested that these athletes supplement with Vitamin D.

Antioxidants (Vitamin C and E, Beta-Carotene, and Selenium):
Antioxidants play an important role in protecting cells from oxidative damage. Habitual exercise has been shown to result in an augmented antioxidant system and reduced lipid peroxidation. It is still unclear whether or not exercise increases the need for antioxidant nutrients. Athletes are advised to not exceed the tolerable upper intake level for antioxidants as these nutrients have the ability to become pro-oxidant at higher dosages.

Calcium:
Calcium is especially important for growth, maintenance and repair of bone tissue, maintenance of blood calcium levels, regulation of muscle contraction, nerve conduction, and normal blood clotting. Inadequate dietary calcium and vitamin D increase the risk of low bone mineral density and stress fractures. Current supplementation recommendations for athletes with disordered eating and risk of osteoporosis is 1500mg calcium and 400-800 IU of vitamin D per day.

Iron:
Iron is required for the formation of the oxygen binding/carrying proteins, namely hemoglobin and myoglobin, as well as enzymes involved in energy production. Iron deficiencies are one of the most common nutrient deficiencies among athletes, especially women. Iron requirements for endurance athletes are increased 70% with vegetarian and athletes who donate blood potentially requiring more. Taking measures to prevent iron deficiency are especially important due to the fact that reversing it can take anywhere from 3 to 6 months. Supplementation with iron in those who are deficient can improve work capacity, endurance, oxygen uptake, reduce lactate concentrations, and reduce muscle fatigue.

Zinc:
Zinc is important for growth, building and repair of muscle tissue, energy production, and immune status. In addition, zinc has been shown to affect thyroid hormone levels, basal metabolic rate, and protein use. Athletes, particularly female athletes, are at risk for low zinc status. However, zinc status is difficult to measure because clear assessment criteria have not been established. The benefits of zinc supplementation on physical performance have not been studied in great detail.

Magnesium:
Magnesium plays a role in cellular metabolism, neuromuscular, cardiovascular, immune, and hormonal functions. Low magnesium intakes are more likely in sports that involve weight classes (where athletes may try to “cut” weight before competing), or those such as dance/gymnastics that are more weight conscious.

Sodium, Chloride, Potassium:
Sodium, chloride, and potassium are electrolyte minerals. Many endurance athletes will require more than the upper limit for sodium (2.3g/day) and chloride (3.6g/day), due to that lost in sweat. Plasma potassium concentrations tend to decrease to a lesser degree than sodium during exercise. However it is still important to consume enough potassium.

Hydration:

Dehydration (defined as a loss of >2% of body weight) can drastically decrease performance especially in hot weather. Therefore it is the goal of athletes to achieve euhydration before, during, and after exercise.

Before Exercise:
It is recommended that at least 4 hours prior to exercise, 5-7mL/kg body weight or water or sports drink be consumed. This allows sufficient time for any excess to be excreted.

During Exercise:
Depending on the sport and environmental conditions, sweat rates can range from 0.3 to 2.4 L/hour. In addition to water, sweat also contains approximately 1 g/L of sodium as well as small amounts of potassium, magnesium, and chloride. The goal of fluid consumption during exercise is to prevent a loss of greater than 2% of body weight during activity. The amount of fluid needed will depend on a variety of factors. It is also important to consider that some sports are not conducive to balancing fluid intake and losses during events (ex. rowing). Skeletal muscle cramps are a good indicator of dehydration, electrolyte deficiencies, and also fatigue.

After Exercise:
Rapid and complete recovery from excessive dehydration can be accomplished by drinking at least 16-24oz. of fluid for every pound of body weight lost. However, given adequate time along with normal meals and beverages, rehydration should occur.

Special Environmental Conditions:
The risk for dehydration is dramatically increased in hot and humid environments. In these situations, it is important that athletes remain well hydrated and be assessed for heat-related illness. Dehydration is possible in cold environments, due to increased respiratory losses and sweat losses due to insulating clothing. Also, in cold environments, fluid intake tends to be decreased. At altitudes >2500m, increased fluid losses occur due to increased respiratory losses and decreased appetite.

The Training Diet:

Pre-Exercise Meal:
Eating prior to exercise has been shown to increase performance. This meal should aim to leave the athlete neither hungry nor with undigested food in their stomach. The following general guidelines for meals and snacks should be used:
  • sufficient fluid should be ingested to maintain hydration
  • foods should be relatively low in fat and fiber to facilitate gastric emptying and minimize gastrointestinal distress
  • meal should be high in carbohydrate to maintain blood glucose and maximize glycogen stores
  • meal should be moderate in protein, and familiar to the athlete
It is also suggested that larger meals be consumed when there is more time for those meals to digest, while smaller meals be consumed closer to exercise when there is less time for digestion. In addition, athletes should become familiar with pre-exercise meal planning during training so as to optimize this meal prior to events.

During Exercise:
It has been shown that carbohydrate consumption during exercise results in maintenance of blood glucose levels and improved performance. For events longer than 1 hour, it is recommended that an athlete consume 0.7 grams/kg body weight/hour. This should not be consumed at one point during the event, but rather at 15-20 minute intervals throughout. In addition, it is recommended that the carbohydrate be in the form of glucose or a mixture of simple sugars and not fructose alone as this could cause diarrhea or indigestion.

Recovery from Exercise:
The timing and composition of the post-exercise meal is dependent on the length and intensity of the exercise session as well as when the next bout of exercise will occur. For an athlete who competes in one event and has a great length of time before the next event, the post-exercise meal will be less important than for the athlete that has multiple events in one day.

Consumption of carbohydrate within 30 minutes post-exercise will result in higher glycogen levels after exercise than if consumption is delayed 2 hours. Again, the athlete with more than 24 hours before the next event will not need to be as regimented in this practice as the athlete that has less than 24 hours. The intake of simple sugars appears to result in a higher muscle glycogen level than does consumption of low-glycemic index carbohydrates.

Dietary Supplements and Ergogenic Aids:

Sports dietitians and athletes should proceed with caution when considering the use of ergogenic aids due to possible negative side effects, lack of efficacy, and potential contamination of with banned substances. Most ergogenic aids can be classified into one of four categories:
  1. those that perform as claimed
  2. those that may perform as claimed but for which there is insufficient evidence of efficacy at this time
  3. those that do not perform as claimed
  4. those that are dangerous, banned, or illegal, and should not be used
Ergogenic aids that perform as claimed:
  • Creatine: Creatine is currently the most widely used ergogenic aid among athletes trying to build muscle and strength. Creatine has been shown to be effective in exercise requiring repeated bouts of short bursts of high-intensity activity that utilize primarily the ATP-CP energy system. This would include activities such as weightlifting and sprinting, however endurance activities have not shown benefit from creatine supplementation. Although the long-term side effects of creatine are still unknown, supplementation is considered safe for healthy adults.
  • Caffeine: Although caffeine is known for its ability to increase free fatty acids in the bloodstream and sparing of muscle glycogen, it’s supplemental effects are more likely due to its role as a central nervous system (CNS) stimulant. Adverse effects of caffeine include anxiety, jitteriness, rapid heartbeat, gastrointestinal distress, and insomnia.
  • Sports drinks, gels, and bars
  • Sodium Bicarbonate
  • Protein and amino acid supplements
Ergogenic aids that may perform as claimed but for which there is insufficient evidence:
  • glutamine
  • beta-hydroxymethylbutyrate
  • colostrum
  • ribose
  • many others
Ergogenic aids that do not perform as claimed:
  • the majority of ergogenic aids on the market
  • bee pollen
  • chromium
  • vanadium
  • many others
Ergogenic aids that are dangerous, banned, or illegal:
  • androstenedione
  • other anabolic, androgenic steroids
  • ephedra
  • human growth hormone

Additional References:

  1. Turcotte L. Role of fats in exercise. Types and quality. Clin Sports Med. 1999; 18:485–98.
  2. Gabel KA. Special nutritional concerns for the female athlete. Curr Sports Med Rep. 2006; 5:187–91.
  3. Burke LM, Loucks AB, Broad N. Energy and carbohydrate for training and recovery. J Sports Sci. 2006; 24:675–85.
  4. Going S. Optimizing techniques for determining body composition. Gatorade Sports Sci Exch. 2006; 19:101.
  5. Driskell J. Summary: Vitamins and trace elements in sports nutrition. In: Driskell J, Wolinsky I, editors. Sports Nutrition. Vitamins and Trace Elements. New York (NY): CRC/Taylor & Francis; 2006. p. 323–31.
  6. Bahrke M, Yesalis C. Performance-Enhancing Substances in Sport and Exercise. Champaign (IL): Human Kinetics; 2002.
  7. Larson-Meyer D. Vegetarian Sports Nutrition. Food Choices and Eating Plans for Fitness and Performance. Champaign (IL): Human Kinetics; 2007.