Some Effects of Caloric Intake on Nitrogen Balance in Dogs

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Abstract
Dogs were fed a constant casein nitrogen intake of 3.82 gm/day/m2 of probable body surface. Calories were varied by altering dietary carbohydrate. Two responses to a restricted caloric intake were recognized. The first response, obtained with even a slight reduction in dietary calories, was an increase in the excretion of urinary nitrogen without any change in the nitrogen balance index of the dietary protein, a response which reflected an increase in the catabolism of proteins. Continued feeding of a markedly restricted intake depleted the protein stores of the body. The second response was a decrease in the nitrogen balance index associated with a marked increase in the excretion of both body and dietary nitrogen. This second response followed the first in the presence of a severe caloric restriction and was dangerous to the animal. Some animals resisted the second response much more than others, a resistance which was correlated, at least in part, with the magnitude of the protein stores of the body. It is emphasized that responses to a restriction in calories vary with the physiological state of the animal and with the composition of the diet fed.