Much attention has been paid to the beneficial health effect of tea catechins as one of the effective strategies to prevent obesity. The current study was carried out to investigate the role of tea catechins on the utilization of dietary energy sources in rats. The addition of 1% (w/w) tea catechins, mostly in gallate forms, to the diet brought about significant reductions in body weight gains and abdominal adipose tissue weights after 4-wk feeding periods compared to the control. A 2-d output of feces collected at the third week of feeding was significantly increased by a tea catechin diet (average dry weight+/-SD of 7.2+/-1.5 g) over that with a control diet (3.8+/-0.4 g). Only 0.1% of ingested starch appeared in the feces of rats fed the control diet, whereas 4.8% was excreted in the feces of the tea catechin group. Moreover, both apparent digestibility values for lipid and protein in the rats fed tea catechins were also lower than those of the control, suggesting that tea catechins increased the fecal excretion of these energy nutrients. Of the gross energy that the rats consumed from their respective diets during the fecal collection period, 1.6% (for control diet) and 5.8% (for tea catechin diet) were estimated to be excreted in feces. The energy loss originating from carbohydrate should contribute to the overall amount of energy in the feces, followed by protein. Intake of tea catechins suppressed the intestinal absorption of energy nutrients via the inhibition of digestive enzymes, which may at least partially influence the body fat reduction by tea catechins.