Flavour-specific anticipatory hunger reinforced by either carbohydrate or protein

Recent evidence indicates that rats can learn to avoid aversive consequences of several hours of food deprivation by eating more of food having orosensory characteristics that predict a protracted fast. Two new studies tested if macronutrient composition of a flavoured meal before the reinforcing fast influences this acquisition of anticipatory hunger/satiety in a smooth-brained mammal. In one study, female Sprague-Dawley rats were trained for 11 cycles of 4 days with experimental meals of either carbohydrate or protein flavoured with either grape or cherry, with one odour followed by a 3-h fast and the other by 10 h of food deprivation. Both nutrient groups acquired anticipatory hunger. Then that learnt increase in meal size started to extinguish the hunger-avoidance response to the longer fast. The other study tested if this finding extended to experimental meals that combined carbohydrate and protein, and had vanilla or chicken flavours, to fasts of 4 and 12 h and to male rats as well as females within a training period of 6 cycles of 4 days. Evidence of anticipatory hunger early in training was clear only in the males. The combined results from the two experiments indicate that either carbohydrate or protein is sufficient for negative reinforcement of flavour-specific anticipatory hunger when the shorter fast lasts for 3 h. This food-discriminative anticipatory adjustment of meal size could be an automatically learnt part of hunger management for socially scheduled eating in human beings.