We investigated whether a structured medium- and long-chain triacylglycerols (MLCT) diet could decrease accumulation of body fat in healthy humans. The study was conducted under a double-blind randomized design. Ninety-three subjects participated in this study. However, 10 subjects could not consume the specified meal, and one subject wished to opt out. Consequently, the study included 82 subjects. The experimental subjects consumed the test bread, which was made with 14 g of MLCT containing 1.7 g MCFA, daily at breakfast during the study period of 12 weeks, and the control subjects consumed bread made with long-chain triacylglycerols (LCT). All subjects consumed the same standard packaged meals. Body composition parameters were body weight, total body fat and abdominal fat, and blood analyses included serum cholesterol, triacylglycerols and phospholipids. Significant decreases of body weight, the amount of body fat, subcutaneous and visceral fat were noted in the MLCT group as compared with those of the LCT group for 12 weeks (P<0.05). Furthermore, a significant decrease in serum total cholesterol was noted in the MLCT group as compared with that of the LCT group at 8 weeks (P<0.05). However, other serum parameters were not different between the MLCT and LCT groups. The results suggest that the daily intake of MLCT diet could result in a reduction in body weight and in accumulation of body fat, and, moreover, it could reduce serum total cholesterol.