Abstract
Athletes training and competing for endurance events have very high energy requirements. They are advised to eat a high carbohydrate diet, to achieve maximum glycogen stores and prolong endurance performance. Diets higher in fat could provide an easier means of consuming the high energy intakes required. They are not recommended because of the potentially adverse effects on plasma lipids and lipoproteins and because a high carbohydrate diet is considered necessary for achieving maximum glycogen stores.
I have compared the effects of diets high in carbohydrate, HC, (60- 65% total energy from carbohydrate, 15-20% from fat) or relatively high in fat, HF, (35-40% energy from carbohydrate, 45-50% from fat) on plasma lipids and lipoproteins in endurance cyclists during a 3-month and extended to four month training period. Thirty-five cyclists were studied for twelve weeks and twenty-two continued the study for an additional four weeks. There were no significant differences in blood lipid and lipoprotein levels between the two diet groups throughout the study. However, plasma TC (p=0.011), LDL-C (p=0.013) and apo B (p=0.024) significantly decreased and apo Al increased significantly (p=0.015) in both groups from baseline to week twelve. The HDL-C/LDL-C (p=0.003) and HDL-C/TC (p=0.001) ratios increased significantly in both groups over the same period. A similar reduction in TC (p=0.007) and LDL-C (p=0.008) was present to week sixteen, as well as a significant increase in HDL-C (p=0.004) and HDL3-C (p=0.009) and a significant decrease in TG (p=0.006) in both groups. An increase in physical fitness and training throughout the study is likely to account for these favourable changes in plasma lipids and lipoproteins.
In addition, there were no significant differences in physical fitness, physical performance, body weight and total body fat between the two study groups throughout the study.
The findings suggest that exercise produces favourable effects on plasma lipids and lipoproteins and this effect persists over a wide range of dietary intakes in endurance athletes involved in a high volume of training. Proscriptive dietary advise may be unnecessary for endurance athletes and a dietary regimen of their preference, within certain limits, may be more appropriate.