The effects of high-carbohydrate and high-fat diets on the serum lipid and lipoprotein concentrations of endurance athletes

We examined the effects of high-carbohydrate and high-fat diets on the serum lipid levels of distance runners. For seven days before each study, subjects consumed a diet containing 15% protein, 32% fat, and 53% carbohydrate. During 14-day experimental periods, a control group (n = 10) continued the same diet while two other groups consumed 69% of their calories as either carbohydrate (n = 13) or fat (n = 14). High-density lipoprotein (HDL)-cholesterol decreased 9% during the high-carbohydrate diet because of a 26% fall in the HDL 2 fraction (1.063 to 1.125 g/mL). These changes were not accompanied by changes in the levels of apolipoproteins (apo) A-I or A-II. Total and low-density lipoprotein (LDL)-cholesterol initially decreased but subsequently exceeded pre-diet values while triglyceride concentrations increased 30% to 50%. Postheparin lipoprotein lipase activity (LPLA) fell 20%. Despite these dietary effects, HDL and HDL 2 cholesterol concentrations in the athletes remained above values typical of sedentary men. The high-fat diet produced different effects on the serum lipids and lipoprotein levels of the athletes. HDL levels changed little during the study although HDL-cholesterol and apo A-I on the last diet day were both slightly above initial values. The high-fat diet provided 111 g of saturated fat per day but had surprisingly little effect on total and LDL-cholesterol whereas serum triglycerides fell by 10% to 20%. Postheparin LPLA increased 30% with fat feeding and the changes in LPLA correlated with alterations in triglyceride levels ( r = −0.53, P < 0.05). We conclude that the lipoprotein levels of endurance athletes are sensitive to changes in dietary fat and carbohydrate. It appears unlikely, however, that diet alone accounts for the runners' higher HDL levels. Diet-induced triglyceride changes may be mediated in part by changes in LPLA.