The Effects of Caloric Restriction on Skeletal Growth

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Abstract
In young rats the rate of skeletal growth was roughly proportional to the rate of general body growth when caloric restriction was the limiting growth factor. Restriction of caloric intake to about one-half of that of ad libitum fed control animals, while ensuring an adequate supply of all other nutrients, resulted in a complete cessation of both skeletal and generalized body growth. Histologically the bones of such animals were identical with those usually found in “partial inanition.” In larger, not quite completely grown rats, caloric restriction, sufficient to cause a loss of 40% of their initial body weight, only slightly decreased the rate of skeletal growth. The plasma concentration of calcium was normal in all animals, while that of inorganic phosphate was below normal in the young caloric-restricted animals but not in the older rats. Caloric restriction in young rats, older rats and parathyroidectomized older rats resulted in a markedly elevated plasma alkaline phosphatase activity. However, it is thought that these latter changes in the caloric restricted rats are due to an altered hepatic carbohydrate metabolism rather than to the defective bone metabolism.