The effect of high fat and high carbohydrate cafeteria diets on diet-induced thermogenesis in the rat.

Young rats fed cafeteria diets of mixed composition, high fat or high carbohydrate (CHO) content exhibited hyperphagia, but the high-fat diet produced the largest, and the high-CHO the smallest increases in energy intake compared to stock-fed controls. Energy expenditure was increased and energetic efficiency reduced by all forms of the cafeteria diet, thus minimizing excess body energy and weight gains. Hypertrophy of brown adipose tissue (BAT) occurred in all cafeteria-fed rats. In separate rats fed a mixed composition cafeteria diet, the acute thermic response to fat was slightly greater than that to CHO, but for stock-fed controls the response to both nutrients was similar. Fat produced increases in thermogenesis in the acute and chronic experiments that were as large as those due to CHO, and these could be due to activation of the sympathetic nervous system or to direct stimulation of BAT metabolism.