Our objective was to study the relationship between the satiety induced by high-protein meals and the activation of brain areas involved in the onset of satiety. In rats, we used immunohistochemistry to monitor brain centers activated by a meal by receiving information from the gastrointestinal tract or via humoral pathways. In the nucleus of the solitary tract (NTS), the acute or chronic intake of high-protein meals led to increased activation of the noradrenergic/adrenergic neurons involved in cholecystokinin-induced satiety. In the arcuate nucleus of the hypothalamus, the melanocortin pathway was also more strongly activated after the acute or chronic intake of high-protein meals. Moreover, the glucagon-like peptide 1 pathway arising from the NTS, which is triggered, among other behaviors, during nonphysiological anorexia, was not activated by high-protein meals, supporting the lack of aversive behavior associated with this diet. Taken together, these results show that the ability of high-protein meals to inhibit food intake occurs alongside the activation, in nutrient-sensitive brain areas, of several specific neuronal populations involved in satiety.
This study was designed to characterize the suppressant effect of yeast protein and purified peptides on energy intake. For this purpose, 5 experiments were carried out using adult male Wistar rats. Rats that consumed ad libitum a standard yeast protein diet ate significantly less and were leaner over 21 d than rats that consumed ad libitum a standard milk protein diet (Expt. 1). Moreover, rats fed a high yeast protein load reduced their next meal and daily energy intake more than rats fed any other well-balanced, amino acid, high protein load (soy, total milk protein, or wheat gluten) and more than those fed a wheat starch diet (Expt. 2). Purified peptides from the yeast protein extract produced similar effects on subsequent energy intake (Expt. 3). Study of the behavioral satiety sequence showed that rats consuming P14-y or P55-y diets ad libitum did not acquire a conditioned food aversion (Expt. 4). Finally, a preliminary study of gastric emptying in rats fed yeast protein loads showed that yeast protein was emptied more rapidly through the pylorus than total milk protein during a meal, which may induce satiety (Expt. 5). Taken together, these experiments show that yeast proteins enhance satiety in rats more than other proteins.
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