Sports Performance and Nutrition


Part I – Energy Requirements for Athletes

Part II – Nutritional Guidelines  |  Part III – Food Choices  |  Part IV – Hydration and Supplements

If you are serious about athletics, or know someone who is, you already know that athletes are a slightly different breed of human.  They flirt with the extreme limits of human physiology, and feed off the adrenaline it produces.  Their success often hinges on the most seemingly nominal criteria: seconds, ounces, and inches.  Athletes rarely stay content with their progress for long, as a benchmark reached ultimately gives rise to another.  They are in a constant strive to become stronger and faster, using the old adage “practice makes perfect” as a motivator to press forward.  But no matter where a person falls on the athletic spectrum of recreational to elite, practice will only ever be half the battle.  Poor or inadequate nutrition is often implicated in declining physical performance in athletes (1).

Science demonstrates how athletic performance changes based on nutritional intake.  Athletes who reach and maintain peak performance are consistently the ones who best provide the requisite energy to fuel activity (2).  These people are able to efficiently convert stored energy in to the power and endurance necessary for athletic success.  In order to achieve this, athletes must be vigilant to not only consume the best types of calories, but also the correct amounts.

At its simplest physical level, the human form is basically a massive lump of stored energy.  We eat energy, in the form of calories to fuel all of the functions that are necessary to live: respiration, circulation, movement, etc. This caloric demand increases proportionally with the number of calories expended in physical activity.  Hence, athletes who tend to be very active, have a higher caloric need than the average person.  To fully understand what is going on only requires a simple understanding of mathematics:

Calories eaten – calories required = net calories

When more calories are eaten than are required, net calories are positive, the extra calories are stored for future use as fat, and we gain weight.  When fewer calories are eaten than are required, net calories are negative, our energy stores shrink, and we lose weight.  Any severe imbalance, surplus or deficit, has metabolic implications that diminish athletic performance (3).  The key to optimal athletic fuelling thus comes down to balance, where the net calories are effectively zero—that is, in a neutral state, where the number of calories eaten roughly matches the number of calories required.

Determination of the ideal caloric intake for individual athletes is very important, but unfortunately, outside the scope of this article.  In general, a person is consuming the correct caloric intake if they have sufficient energy to compete in their sport without large fluctuations in weight.  So long as a person avoids large magnitude deficits and surpluses in energy level, the metabolism appears to be able to self-regulate (4).

Existing in an energy neutral state may be ideal for an athlete at their desired body composition, but what about athletes who want to gain, or more commonly, lose weight?  They must do so carefully, so to not impact athletic performance.  Severe caloric restriction causes the metabolism to drop in order to preserve energy (5), which means that the body focuses on nutrient conservation and hinders energy usage in physical activity.  When caloric restriction ends, the body reacts by storing calories, which ultimately results in rebound weight gain (5).  Hence, severe calorie restriction not only impedes athletic performance, but also yields only temporary weight loss.  Conversely, athletes who seek to gain weight by grossly over-consuming calories, no matter how rigorous their training schedule, risk decline in athletic performance by storing excess nutrients as fat rather than desired muscle (6).  The key to modifying weight and body composition is to do so with no more than a 10-20% increase or decrease from their pre-determined energy neutral intake (7).


Read more in this four-part Sports Nutrition series:
Part I – Energy Requirements for Athletes
Part II – Nutritional Guidelines for Athletes
Part III – Food Choices for Athletes
Part IV – Hydration and Supplements for Athletes

1. Costill D, Flynn M, Kirwan J, Houmard J, Mitchell J, THomas R, et al. Effects of repeated days of intensified training on muscle glycogen and swimming performance. Med Sci Sports Exerc. 1988 June; 20(3): p. 249-254.

2. Costill D. Carbohydrates for exercise: dietary demands for optimal performance. International Journal of Sports Medicine. 1988; 9: p. 1-18.

3. Economos C, Bortz S, Nelson M. Nutritional Practices of Elite Athletes. Sports Medicine. 1993 December; 16(6): p. 381-399.

4. E S, S R. The role of energy expenditure in energy regulation:findings from a decades of research. Nutrition Reviews. 1995; 53: p. 209-220.

5. Moriguti S, McCror M, Saltzman E, Mosunic G, Greenberg A, Roberts S. Effects of a 6-week hypocaloric diet on changes in body composition, hunger, and subsequent weight regain in health young and older adults. Th Jounals of Gerontoloy: Series A Cognition, Health, and Aging. 2000; 55(12): p. B580-B587.

6. Forbes G, Brown M, Welle S, Lipinski B. Deliberate overfeeding in women and men: Energy cost and composition of weight gain. British Journal of Nutrition. 1986; 56: p. 1-9.

7. American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine. Position paper: Nutrition and athletic performance. Journal of the American Dietetic Association. 2000; 109(3): p. 509-527.