Nutrition and Exercise Introduction and Overview

Abstract

Concern with physical fitness has heightened inter est in nutrition in relation to exercise physiology and biochemistry. This was evidenced by 400 participants in this symposium in which seven contributions were presented. The symposium was opened by Dr. Vishwa Singh, who presented an overview on nutrition and exercise. In his overview, Dr. Singh drew attention to the role of oxidative damage that occurs in exercise, which also contributes to the etiology of certain chronic diseases in aging. Evidence has been accumulating to suggest that ex ercise is damaging. Stable free radical accumulation has been observed in skeletal muscles after exercise, and it has also been reported that vitamin E deficiency exacerbates the leakage of skeletal muscle enzymes into the blood. A change in the redox status of blood antioxidants is shown with glutathione oxidation dur ing exercise; this has been observed not only in human blood, but also in animal tissues. There is evidence that some tissues suffer an ischemia-reperfusion type of injury after exercise; i.e., those tissues that have reduced circulation during exercise experience a reoxygenation burst immediately after cessation of exer cise. Dr. Singh pointed out that there is some evidence that antioxidant nutrients (vitamin C, vitamin E and /3-carotene)can minimize the oxidative damage during exercise. Furthermore, nutrition and exercise seem to share their roles in prevention/management of certain chronic diseases (i.e., hypertension, coronary heart disease, cancer and osteoporosis). Thus, Dr. Singh proposed that proper nutrition, particularly adequate intake of antioxidant nutrients, be made an integral part of the regular exercise regimen for prevention of disease and promotion of optimal health. The importance of antioxidants in minimizing in dices of oxidative damage was investigated in both human and animal studies as reported by Dr. Lester Packer and his colleagues. In moderately trained hu mans it was found that repeated sessions of mild ex ercise did not increase urinary output of an oxidatively modified RNA base, 8-hydroxyguanosine, nor did supplementation with vitamins Eand C and /3-carotene have an effect on its excretion. Substantial increases in plasma concentrations of the antioxidants occur as a result of supplementation. This study showed that exercise induces increases in plasma vitamin C con centration. The percentage of the vitamin C in the reduced form also increases. Because a large oxidation of blood glutathione occurred during exercise, it was suggested that some of the reducing equivalents from glutathione might be used to increase the proportion of plasma vitamin C in its reduced form. In another study with endurance-trained rats, it was found that such training causes a doubling in oxida tively modified protein in muscle, as measured by protein carbonyls, which return to normal levels with detraining. No changes in protein carbonyl content of liver with training or detraining were seen. It is known that dietary (energy) restriction results in prolongation of life span. It is still unclear, however, whether exercise has positive or negative effects on longevity. Effects of exercise and food restriction on longevity were investigated by Dr. John O. Holloszy's laboratory.