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Summary:

In addition to being a source of essential nutrients for our body, dietary proteins participate in the regulation of energy homeostasis. In a context of obesity epidemic and food overconsumption, the characterization of the role of proteins on health becomes crucial. In general, proteins are known to reduce food intake by stimulating satiety and improving glucose homeostasis, but very few studies have focused on comparing the effects of protein origin on these phenomena. The objective of this work is to compare proteins of different origins on certain homeostasis mechanisms involved in the peripheral regulation of food intake and glucose metabolism. Proteins from various sources of animal or plant origin were thus selected: bovine hemoglobin, caseins, ovalbumin, whey, fish gelatin, peas and gluten. These proteins were first studied and compared in vivo in rats. A first study using metabolic cages determined the effect of proteins on short-term food intake, energy expenditure, gas exchange coefficient, and locomotor activity. A second study investigated the effect of proteins on the regulation of intestinal glucose absorption, on the modulation of the secretion of intestinal hormones and on the inhibition of the DPP-IV (Dipeptidyl peptidase IV) activity and a third study was carried out to determine the effect of proteins on glucose homeostasis.

In parallel, complementary functional studies were carried out ex vivo on parts of rat intestine and in vitro on different intestinal cell models. The proteins were then digested using a static gastrointestinal digestion protocol suitable for the digestion of proteins alone. The results obtained globally highlight an effect of the protein source on energy homeostasis via different action on the followed markers. This work also highlights, for the first time, that an acute protein intake could improve glucose tolerance by inhibiting its absorption by the intestine. Indeed, protein digests were able to decrease intestinal glucose absorption in vitro and ex vivo and acute ingestion of fish casein and gelatine improved glucose tolerance in rats without significant effect on insulin secretion. All of these studies have highlighted the importance of proteins in the mechanisms for regulating energy homeostasis through their interactions on markers of glucose metabolism and food intake, which are both very closely linked. Proteins, depending on their origin, modulate more or less the secretion of satietogenic and pancreatic hormones, the activity of DPP-IV and the intestinal glucose absorption.

The jury was composed of :

•     Didier Remond, Maitre de conférences (HDR), Université de Clermont-Ferrand, Rapporteur
•     Claude Knauf, Professor, University of Toulouse, Rapporteur
•     Claire Gaudichon, Professor, AgroParisTech, Examiner
•     Michelle Bastide, Senior Lecturer (HDR), University of Lille, Examiner
•     Rozenn Ravallec, Professor, University of Lille, Thesis Director
•     Benoit Cudennec, Associate Professor (HDR), University of Lille, Thesis Supervisor
•     Camille Dugardin, PhD, Research Engineer, UMRT 1158, Guest
•     Pascal Dhulster, Professor, University of Nîmes, Guest

Many congratulations.