Insulin suppresses intake without inducing illness in sham feeding rats

Insulin's effects on consumption were investigated in rats feeding with open gastric cannulas. Insulin produced small but statistically reliable decreases in sham intake. Intake was reduced during the one-hour sham feeding interval by 11 to 18%, however, the second, third and fourth 15-min intervals were reduced by 20 to 33%. An initial increase (first 15 min of sham feeding) following insulin injection offset somewhat insulin's suppressive effects on sham intake. All reductions were obtained by comparing sham intake following 0.1 to 0.75 U insulin per rat to intake following saline. When insulin or saline injections were paired with alternatively flavored sweetened condensed milk during sham feeding, subjects preferred the insulin-paired flavor in a subsequent two-bottle test. After just 6 complete pairings, insulin-paired, flavored milk was preferred at a ratio of almost six to one. The results indicate the effectiveness of insulin in inhibiting intake in a situation in which the actions of other potential satiety mechanisms are minimized. Additionally, insulin accomplishes this without inducing a flavor aversion for the milk sham consumed.