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Energy Balance and Mitochondrial Function in Liver and Brown Fat of Rats Fed "Cafeteria" Diets of Varying Protein Content^1,2,

Department of Physiology, St. George's Hospital Medical School, Tooting, London SW17 ORE, U.K.

Rats fed "cafeteria" diets with low (7%, LP) normal (23%, NP) or high (33%, HP) protein contents showed increases in metabolizable energy intake (kJ/kg^0.75, 23–41%) and in energy expenditure (36%) compared to controls fed stock diet (27% protein). The high metabolic rates were inhibited by ß-adrenergic blockade with propranolol. All rats fed cafeteria diets deposited more fat than controls, but the LP diet depressed growth, and these animals also showed the lowest energetic efficiency. Brown adipose tissue (BAT) mass and protein content were increased in all groups fed cafeteria diets, but the largest changes occurred in LP-fed animals, and the smallest in the HP group. Hepatic mitochondrial -glycerophosphate shuttle activity and plasma triiodothyronine levels were elevated twofold in rats fed LP cafeteria diet compared to controls, but the other cafeteria diet groups showed little or no changes, and shuttle activity in BAT was not affected by any of the diets. Blood glucose and plasma insulin levels were similar for control, NP and HP animals, whereas glucose levels were slightly lower and insulin levels were very much lower in the rats fed LP cafeteria diet.

KEY WORDS: • diet-induced thermogenesis • cafeteria diet • protein intake • brown adipose tissue • rat

¹ This work was supported by grants from the National Science Foundation, U.S.A. (R.S.T.) and The Royal Society (N.J.R.).

² A preliminary report of these results has been presented to the Nutrition Society, May 1982.

³ Permanent address: Department of Human Nutrition & Foods, University of Vermont, Burlington, Vermont 05405.

Manuscript received 11 March 1982.