Triacylglycerols containing medium- and long-chain fatty acids (TML) have medium- and long-chain fatty acids in the same molecule. The effects of dietary TML on serum lipid levels and body fat were studied in six young men belonging to a university rowing club. A double-blind crossover study was performed in which for 3 wk the subjects ingested a liquid diet containing 20 g/d of soybean oil or TML in addition to their regular diets. Throughout the study, they were asked to keep their usual lifestyle, including diet and physical activity. The body composition of the subjects was measured weekly. Blood samples were taken at 0, 2, and 3 wk of each treatment period. There was no significant difference in energy intake between the soybean oil diet period and the TML diet period. The rate of variation of serum triacylglycerol concentration was significantly lower after a consumption of the TML liquid diet for 3 wk compared with the soybean oil liquid diet. The rate of variation of body fat mass was also significantly lower after a consumption of the TML liquid diet for 3 wk compared with the soybean oil liquid diet. However, the serum cholesterol concentration did not change significantly during either dietary treatment. These results suggest that TML, compared with soybean oil, may have the potential to prevent hypertriglyceridemia and obesity caused by consumption of a high-fat diet.