Differential effects of intravenous glucose, amino acids, and lipid on daily food intake in rats.

Three types of nutrient were infused intravenously for 30 min before and during the 17 h when rats were fed to assess the effects of these nutrients on short-term and daily food intake. Infusions of glucose (34 kcal/day for 4 days) reduced food intake from saline baseline levels by 18.8 +/- 1.9 kcal/day. This represents an oral intake reduction equivalent to 55% of each calorie infused. When amino acids were delivered intravenously at 10 and then 20 kcal/day for 4 days, food intake was reduced by 11.9 +/- 1.4 and 20.4 +/- 2.4 kcal/day, which represent oral intake reductions of 112 and 103% of infused calories, respectively. Food intake was reduced 8.2 +/- 0.5 and 16.6 +/- 1.4 kcal/day (or 41 and 42% of calories infused), when a lipid emulsion was delivered at 20 or 40 kcal/day for 6 days, respectively. A combination of all three nutrients (i.v. diet composed of 50% glucose, 13% amino acids, and 37% lipid by calories) identical to the nutrient composition of the oral diet was infused at 20 and then 40 kcal/day for 6 days. Food intakes were reduced by 14.8 +/- 2.0 and 32.3 +/- 3.3 kcal/day, representing 74 and 80% of infused calories. Recovery of food intake to previous saline baseline levels was rapid and complete after the glucose and amino acid infusions but was delayed and incomplete after the lipid and intravenous diet conditions. These results indicate that infused amino acids or a balanced intravenous diet is more effective than glucose or fats in inhibiting daily food intake.