Studies in animals and humans indicate that diets containing diacylglycerol (DAG) oil (containing >80% DAG) decrease body weight gain and body fat accumulation, especially visceral fat. Body weight and body fat are controlled by energy expenditure, fat oxidation, fat storage capacity, and appetite control. Recent researches indicate that DAG oil, compared with conventional oils, has distinct metabolic effects. We review the evidence concerning the effects of DAG oil intake on fat oxidation and energy expenditure. In humans, dietary DAG is more susceptible to oxidation, and in animals 1,3-DAG, a major component of DAG oil, is rapidly oxidized. Short-term human studies with indirect calorimetry demonstrate greater fat oxidation with DAG oil consumption compared with triacylglycerol (TAG) oil consumption. Furthermore, DAG oil consumption for 14 days stimulates energy expenditure. Based on these reports, enhanced fat oxidation and energy expenditure by daily DAG oil intake could contribute to long-term reductions in body weight and fat accumulation. The literature provides support for the notion that dietary DAG is more rapidly oxidized than dietary TAG, and that, compared with TAG oil, DAG oil consumption increases whole body fat oxidation. The effects of DAG oil consumption on energy expenditure, however, remain inconclusive. (c) 2009 International Union of Biochemistry and Molecular Biology, Inc.