Prolonged adaptation to fat-rich diet and training; effects on body fat stores and insulin resistance in man

OBJECTIVE: To investigate the effect of prolonged adaptation to training and fat- or carbohydrate-rich diet on body composition and insulin resistance. DESIGN: Longitudinal study. Of three groups two consumed a fat-rich diet, of which one performed regular training (FAT-Train, n = 17) and the other maintained normal habitual activity (Fat-Control, n 8). The third group trained and consumed a carbohydrate-rich diet (CHO-Train, n = 16). SUBJECTS: Forty-one untrained, healthy male subjects. MEASUREMENTS: Before and after 7 weeks body composition was estimated from skinfold measurements, At rest the respiratory exchange ratio (RER) was determined by the Douglas bag technique. Glycogen was determined in m vastus lateralis and concentrations of insulin and triacylglycerol in serum and glucose, fatty acid and beta-hydroxy-butyrate in plasma was measured. The insulin resistance index was calculated from fasting plasma insulin and glucose values. RESULTS: Across the 7 weeks body weight was reduced (1.3 +/- 0.3%) in all three groups, however body fat mass was decreased only in the CHO-Train (13%) and maintained in the two FAT-groups. RER at rest was similarly decreased (5%) in the three groups. Plasma insulin tended to decrease (16%) in CHO-Train (P 0,065) and remained unchanged in the two FAT-groups. In contrast plasma glucose (4.6 +/- 0.1 mmol/l) and plasma FA (453 +/- 27 mumol/l) remained unchanged across the 7 weeks. The calculated insulin resistance index HOMA-R-mod was significantly decreased by 19% in CHO-train but remained unchanged in both of the FAT-groups, whereas the calculated insulin secretion index HOMA-beta(mod) was unchanged in all three groups, CONCLUSION: In the present study we demonstrate that despite of a mild energy deficit body fat mass was maintained after prolonged adaptation to fat-rich diet both when normal physical activity was maintained and when training was performed. In contrast a significant decrease in fat mass was observed when carbohydrate-rich diet and training was combined. Furthermore we observed that the insulin resistance index was significantly decreased only when training was combined with a carbohydrate-rich diet.