Protein is more potent than carbohydrate for reducing appetite in rats

The purpose of this study was to characterize further the effects of loads of protein versus carbohydrate on subsequent food intake in rats. We used an intraoral cannula to deliver isoenergetic isovolumic loads, in a tightly controlled time frame allowing for both metabolic responses and orosensory components of the load. Our results showed that the gluten load (GLT-100%) induced a greater depression in food intake than an isocaloric wheat starch load (GLT-0%). The types of protein used in the load (total milk protein vs. GLT) did not seem to influence their appetite-suppressive effect. There was a dose-dependent effect of the satiating effects of the protein loads, the GLT-100% load being more effective than either the GLT-35% or GLT-50% loads. Pattern analysis of the meal following the load suggested that animals were more satiated by protein, at least when loads contained 35% or 50% of protein, than by carbohydrate. At least 1 day was necessary before we saw a significant decrease in the energy intake following the protein loads. Thus, the animals had to learn the postingestive effects of the loads before the response stabilized. Taken together, the present results confirm that protein has a greater satiating effect than carbohydrate and extend these results by revealing that the larger the proportion of protein in the food, the larger the satiating effect, and that the quality of protein does not seem to play a significant role.