The effects of a liquid-formula diet supplement containing structured medium- and long-chain triacylglycerols (SMLCT) composed of medium- (10%) and long-chain (90%) fatty acids were compared with those of long-chain triacylglycerols (LCT) on bodyfat accumulation in 13 healthy male volunteers aged 18-20 years. The subjects were randomly assigned the SMLCT or LCT group. The subjects in each group received a liquid-formula diet supplement of the SMLCT or LCT, which provided 1040 kJ plus daily energy intake for 12 weeks. Mean energy intake containing liquid diet throughout the 12-week period did not differ between the SMLCT and LCT groups. Bodyweight of subjects in both groups increased slightly from the baseline throughout the 12-week period, but the differences were not significant. Rates of variation of bodyfat percentage were significantly lower in the SMLCT group than in the LCT group throughout the 12-week period. Comparisons between the SMLCT and LCT groups at baseline and 12 weeks showed no significant differences in any of the biochemical blood parameters. These results suggest that replacing LCT with SMLCT over long periods of time could produce bodyfat loss in the absence of reduced energy intake.