Effects of isoenergetic overfeeding of either carbohydrate or fat in youngmen

Ten pairs of normal men were overfed by 5 MJ/d for 21 d with either a carbo hydrate-rich or a fat-rich diet (C- and F-group). The two subjects in each pair were requested to follow each other throughout the day to ensure simil ar physical activity and were otherwise allowed to maintain normal daily li fe. The increase in body weight, fat free mass and fat mass showed great va riation, the mean increases being 1.5 kg, 0.6 kg and 0.9 kg respectively. N o significant differences between the C- and F-group were observed. Heat pr oduction during sleep did not change during overfeeding. The RQ during slee p was 0.86 and 0.78 in the C- and F-group respectively. The accumulated fae cal loss of energy, DM, carbohydrate and protein was significantly higher i n the C- compared with the F-group (30, 44, 69 and 51 % higher respectively ), whereas the fat loss was the same in the two groups. N balance was not d ifferent between the C- and F-group and was positive. Fractional contributi on from hepatic de novo lipogenesis, as measured by mass isotopomer distrib ution analysis after administration of [1-C-13]acetate, was 0.20 and 0.03 i n the C-group and the F-group respectively. Absolute hepatic de novo lipoge nesis in the C-group was on average 211 g per 21 d. Whole-body de novo lipo genesis, as obtained by the difference between fat mass increase and dietar y fat available for storage, was positive in six of the ten subjects in the C-group (mean 332 (sem 191) g per 21 d). The change in plasma leptin conce ntration was positively correlated with the change in fat mass. Thus, fat s torage during overfeeding of isoenergetic amounts of diets rich in carbohyd rate or in fat was not significantly different, and carbohydrates seemed to be converted to fat by both hepatic and extrahepatic lipogenesis.