Effects of dietary protein and exercise on brown adipose tissue and energy balance in experimental animals.

The effects of exercise and of dietary protein level on energy metabolism and brown adipose tissue (BAT) activity were investigated in weaning male mice. Mice were fed diets providing low (7.5%), adequate (12.5%) or high (25%) levels of dietary protein. Half of the animals in each dietary group were given moderate exercise by swimming. The lower the level of dietary protein, the greater the increase in food intake, energy expenditure, body fat and BAT mass; however, total-carcass energy, food efficiency and BAT activity were not affected by the level of dietary protein. In experiment 2, BAT was compared in mice swimming at 33 degrees C and 36 degrees C with non-exercised controls. In a third experiment, energy balance and BAT activity were compared in rats exercised at 36 degrees C and in paired weight gain (PWG) rats whose food intake was restricted to achieve weight gains equal to that of the exercised rats. PWG rats maintained carcass energy content equal to that of the controls and significantly greater than the exercised rats by decreasing energy expenditure. Moderate exercise did not affect food intake, whereas rigorous exercise decreased energy intake. Exercise did not affect BAT mass or thermogenic activity; however, mild cold stress did increase BAT activity. Exercise decreased body fat, carcass energy and food efficiency without affecting BAT.