Milk Proteins and Peptides and Energy Expenditure

The quantity of dietary protein in the diet has been demonstrated to affect food and energy intake, energy metabolism and expenditure, and body weight. Increasing protein content in the diet affects different components of energy homeostasis including a decrease in spontaneous energy intake, a decrease in lipogenesis, an increase in lipolysis, or a modification in insulin secretion and insulin sensitivity. An enhancement of thermic effect of feeding has also been proposed but remains to be confirmed. In humans, high protein diets may prevent the loss of lean body mass during energy restriction and protein supplements helped to limit the weight regain after stopping a very low energy diet.

The nature of the protein in the diet is also suspected to influence the metabolic events directly or indirectly involved in energy control through the kinetic and profile of amino acid release, or to the presence of bioactive components acting on specific targets. Milk proteins are of particular interest as they are made of soluble and non-soluble fractions that exhibit different characteristics. Whey proteins are rapidly digested and are especially rich in branched chain amino acids, lysine, tryptophan and cysteine. In contrast caseins are more progressively digested and absorbed and are especially rich in proline and glutamine. Both fractions have been demonstrated to contain bioactive protein or peptide components.

A modification of milk protein composition could improve their effect on energy metabolism. Different milk casein or whey protein components were shown to differently modulate food and energy intake, glucose metabolism, fatty acid and adipose tissue metabolism, or insulin secretion and sensitivity. These effect of the different milk protein fractions were related to the modulation of different processes including the release of gut peptides (ghrelin, CCK, GLP-1, GIP, …) and hormones (insulin, leptin,…), the synthesis of metabolic components (glutathione, serotonin, catecholamins,…), or different factors involved in the regulation of the cellular signalling in different tissues and organs (AMPK, mTOR,…).