Immunological hazards from nutritional imbalance in athletes.


Shephard RJ, Shek PN




Exerc Immunol Rev


This review examines the influences of nutritional imbalance on immune function of competitive athletes, who may adopt an unusual diet in an attempt to enhance performance. A major increase in body fat can have adverse effects on immune response. In contrast, a negative energy balance and reduction of body mass are likely to impair immune function in an already thin athlete. A moderate increase in polyunsaturated fat enhances immune function, but excessive consumption can be detrimental. Since endurance exercise leads to protein catabolism, an athlete may need 2.0 g/kg protein rather than the 0.7-1.0 g/kg recommended for a sedentary individual. Both sustained exercise and overtraining reduce plasma glutamine levels, which may contribute to suppressed immune function postexercise. A large intake of carbohydrate counters glutamine depletion but may also modify immune responses by altering the secretion of glucose-regulating hormones. Vitamins are important to immune function because of their antioxidant role. However, the clinical benefits of vitamin C supplementation are not enhanced by the use of more complex vitamin mixtures, and excessive vitamin E can have negative effects. Iron, selenium, zinc, calcium, and magnesium ion all influence immune function. Supplements may be required after heavy sweating, but an excessive intake of iron facilitates bacterial growth. In making dietary recommendations to athletes, it is important to recognize that immune response can be jeopardized not only by deficiencies but also by excessive intake of certain nutrients. The goal should be a well-balanced diet.