Energy expenditure of 'cafeteria'-fed rats determined from measurements of energy balance and indirect calorimetry.

1. Energy expenditure was determined in rats fed a standard laboratory diet or a varied and palatable 'cafeteria' diet, from metabolizable energy intake and body energy gain over a 15 d experiment. This was compared with measurements of oxygen consumption (Vo2) made over 24 h during the first and second weeks of the experiment. 2. Metabolizable energy intake was elevated by 50% in 'cafeteria'-fed rats and these animals gained more weight and had a higher body fat content than stock-fed controls. Energy expenditure derived from these measurements was 45% higher in the 'cafeteria' group, and the net efficiency for energy gain was significantly reduced. 3. Vo2 was increased by 45% in the 'cafeteria' group and the daily energy expenditure, estimated from Vo2, was identical to that derived from the energy balance for controls, and differed by only 3% for the 'cafeteria' group. 4. These results confirm the high levels of diet-induced thermogenesis previously seen in hyperphagic, 'cafeteria'-fed rats and reaffirm the validity of the carcass balance method for estimating energy expenditure.