Effect of environmental temperature on energy balance and thermogenesis in rats fed normal or low protein diets

Rats fed a low protein (9% metabolizable energy) diet and housed at 24°C gained less weight and body energy than controls fed a normal (25%) protein diet. Energy intake and expenditure corrected for body size [kJ/(kg0.75·d)] were similar in rats fed the two diets, but energetic efficiency was suppressed in low protein-fed rats, and the thermogenic response to norepinephrine and the activity of brown adipose tissue (mitochondrial GDP binding) were both significantly elevated. Housing at a higher temperature (29°C) suppressed energy expenditure and brown fat activity in animals fed either diet, and gross efficiency was greater in control animals at 29°C than at 24°C but unaffected in the protein-deficient group. The differences in brown fat activity between dietary groups were still apparent at 29°C. The results suggest that thermogenesis induced by feeding low protein diets is not markedly inhibited by a higher environmental temperature.