Parenteral nutrition and oral intake: effect of glucose and fat infusions

The effect of intravenous nutrition on voluntary oral intake was studied in healthy male volunteers. Subjects were confined to the Surgical Metabolic Unit for the 17 to 19 day study and were restricted to commercial liquid diet. Each study consisted of three consecutive phases: (1) Ringer's lactate (RL), (2) peripheral parenteral nutrition (PPN) administered for 5 or 6 days as a combination of glucose (caloric load equal to 34% resting energy expenditure, REE), fat (34% REE), and amino acids (17% REE) or a single nutrient infusion of glucose (68% REE), fat (68% REE), glucose (34% REE), or fat (34% REE), and (3) RL for the third period. When all three nutrients or glucose alone (68% REE) were given, subjects decreased daily voluntary food intake within 24 to 48 hr by an amount that closely compensated for the infused calories. Intake was reduced by only 20% to 40% of the infused calories when fat alone (68% REE) was given. There were no significant effects when the lower levels of glucose and fat were given. These data suggest the presence of a postabsorptive control of food intake in humans that is sensitive to the circulating supply of fuels.