Effect of body weight manipulations on sham feeding in the rat

Rats with chronic esophageal fistulas were permitted to sham-feed a carbohydrate solution (a simplified model food) for a 40-min session each day. Body weight was elevated, then reduced again, by varying the caloric density of the liquid diet by which the rats were maintained. With 1M glucose as tastant, induction of mild obesity caused an abrupt reduction in sham meal size. Sucrose concentration-intake functions were lowered at all concentrations by mild obesity, but without change in slope. Both changes were reversed by weight reduction to around normal body weight; further weight reduction produced no further change. Therefore, some correlate of body weight biases the oral control of bout size. The bias seems to change rather abruptly between one value and another at a weight level slightly above normal.