The interaction of exercise and diet in determining the lipid profiles of endurance athletes is poorly defined. Since active men consume more calories than sedentary individuals, we examined the effects of caloric restriction alone or in combination with exercise cessation on the serum lipid levels of men running 16 km daily. For seven days before each study, subjects consumed diets composed of 15% protein, 32% fat, and 53% carbohydrate. During ten-day experimental periods, one group (n = 10) continued running and consumed the same diet containing 3670 kcal/day, while two other groups consumed an identical diet containing 20% fewer calories and either continued (n = 16) or stopped (n = 15) exercise training. High-density lipoprotein cholesterol (HDL-C) concentrations decreased 1% to 5% in all groups during the seven-day preliminary diet. Additional reductions in total HDL-C concentrations were similar in the control and exercise cessation groups, but HDL2-C level decreased 15% during exercise cessation. During caloric restriction and continued running, in contrast, HDL-C concentration increased 8% and the HDL2-C subfraction increased 23%. There was little change in levels of apolipoprotein A-I concentrations during any of the protocols, demonstrating that changes in HDL-C are not necessarily attended by changes in the major HDL apoprotein. Low-density lipoprotein cholesterol (LDL-C) level decreased 10% to 15% in all groups during the preliminary period. Only small additional reductions occurred in men who continued running. Exercise cessation, however, was associated with a 10% increase in LDL-C level after only two days of inactivity. This was due in part to a 5% decrease in plasma volume which occurred with exercise cessation. The contrasting effects of exercise cessation and caloric restriction suggest that regular endurance exercise training rather than the associated high caloric intake is primarily responsible for the lipoprotein profiles characteristic of distance runners.
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism