FAT AND CARBOHYDRATE METABOLISM IN HUMANS-A Study of Nutritional and Hormonal Effects.

As an index to the rate of fat utilization in human subjects, the recovery of all radioactive carbon dioxide in the expired air was measured for one hour following intravenous injection of palmitate-1-C(14). In the normal fasted subject, about 10 per cent of the injected dose was recovered, and the proportion was lowered to about 5 per cent by administration of glucose. With prolonged fasting, the recovery of radioactive carbon dioxide did not change, despite a rising concentration of fatty acids in the serum. This was interpreted as due to the development of a balance between increasing mobilization and oxidation and was thought to indicate increasing fatty acid oxidation. In chronic undernutrition and diabetes mellitus there was increased fatty acid oxidation due presumably to adaptation to a chronic increase in fat utilization for energy. Administration of human growth hormone did not increase fat oxidation but prevented the usual inhibition produced by glucose. This was interpreted to mean that growth hormone increases fat utilization only indirectly by inhibiting the usual preferential utilization of glucose over fat.