The effects of long term intake of catechins on body fat reduction and energy metabolisms during exercise were investigated, in a controlled clinical trial, to confirm the effects of a combination of exercise with catechin intake that has been reported to be effective in reducing obesity. Healthy male subjects (n = 19, mean age .+-. SEM ; 37.6 .+-. 1.1 yr, mean BMI ; 24.0 .+-. 0.5 kg/m2) were randomly divided into two groups and ingested a test beverage in the form of a sports drink containing 0 mg (control) or 570 mg of catechins for 12 weeks. Anthropometric measurements, CT scans and an exercise tolerance test were performed. Total abdominal fat area and visceral fat area which were almost identical initially became smaller in the catechin group compared to those in the control group, indicating the existence of a significant interaction between catechin intake and the test period for the observed values. The rate of fat oxidation during exercise was increased in association with an increase in the intensity of exercise in the catechin group compared to that in the control group, and a significant interaction between catechin intake and exercise intensity in the .DELTA.(12W-0W) values was noted. The catechin group showed a significant increase in the value of maximal oxygen uptake, an indicator of the endurance capacity and the utilization capacity of aerobic energy, at week 12, compared to the initial value. These results show that the long term intake of catechins contributes to body fat reduction in association with increases in rate of fat oxidation during exercise and the maximal oxygen uptake. An important approach for preventing life-style related diseases, one of the risk factors of which is obesity, is suggested.