Effects of feeding a palatable "cafeteria' diet on energy balance in young and adult lean (+/?) Zucker rats.

1. The effects of feeding a palatable and varied "cafeteria' diet on energy balance were studied in young (5.5 week) and adult (5.5 month) lean male Zucker (+/?) rats. 2. Estimates of metabolizable energy (ME) intake derived from food composition tables were almost identical to values obtained from bomb calorimetry of foods, urine and faeces, and ME intake was elevated by approximately 73% in all "cafeteria' animals compared to stock-fed controls. 3. "Cafeteria' feeding had no effect on the body-weight of young rats but induced excess weight gains in the older animals and resulted in increased deposition of fat and energy in both groups. Energy expenditure, calculated from ME intake and body-energy gain, was elevated by 77 and 57% in young and adult-cafeteria rats respectively. The energy cost of fat deposition could account for only a small proportion of this increased expenditure. 4. The present results confirm previous findings in another strain of rat and show that the increased energy expenditure (i.e. diet-induced thermogenesis, DIT) which occurs in response to hyperphagia is not restricted to young animals but is also seen in older rats. Measurements of resting oxygen consumption after injections of noradrenaline or a beta-adrenergic antagonist (propranolol), and changes in brown adipose tissue mass are consistent with the suggestion that the DIT of "cafeteria'-fed rats results from sympathetic activation of brown fat.