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 degrees C gained less weight and body energy then controls fed a normal (25%) protein diet. Energy intake and expenditure corrected for body size [kJ/(kg0.75 X 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 degrees C) suppressed energy expenditure and brown fat activity in animals fed either diet, and gross efficiency was greater in control animals at 29 degrees C than at 24 degrees C but unaffected in the protein-deficient group. The differences in brown fat activity between dietary groups were still apparent at 29 degrees C. The results suggest that thermogenesis induced by feeding low protein diets is not markedly inhibited by a higher environmental temperature.