The protein-sparing action of protein feeding: absence of relationship to insulin secretion.

The influence of a 2-day fast was compared with that of a modified fast (1.5 g beef protein hydrolysate per kg body wt) on nitrogen metabolism and insulin secretion in three normal young men. During the fast urinary urea excretion indicated a negative nitrogen balance of 10 to 12 g daily in each subjects. With protein feeding nitrogen equilibrium was approached in each instance. Insulin secretion as indicated by the urinary excretion of C-peptide dropped profoundly with fasting to levels which averaged just 13 to 22% of the control base-lines and remained at about these levels during the protein feeding. The fact that this sensitive indicator of insulin secretion disclosed no significant difference during fasting and protein feeding provides strong evidence that the protein-sparing influence of protein feeding cannot be ascribed to the decline in insulin secretion.