Whey protein and satiety in humans : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Nutritional Sciences at Massey University, Manawatu campus, Palmerston North, New Zealand
Protein is the most satiating macronutrient and there is an effect of dietary protein source, with dairy whey protein being particularly effective in promoting satiety in adult humans. The underlying cause for this remains to be elucidated. The objectives were to confirm that whey protein is more satiating than maltodextrin carbohydrate in adult humans, to understand the potential mediating factors and to investigate which characteristic of whey protein gives rise to its satiating effect. Ad libitum food intake at a subsequent test meal after administration of a preload, subjective feelings of appetite (using visual analogue scales) and plasma concentrations of satiety-related hormones and metabolites were determined. Preload diets enriched with whey protein induced a greater reduction in subsequent food intake and suppression in rated feelings of appetite compared with maltodextrin carbohydrate (p<0.05). The time of consumption of the whey protein preload did not influence the satiety response. Plasma concentrations of pancreatic polypeptide hormone, total amino acids, and the branched-chain amino acids appear to play an important role in mediating the satiating effect of whey protein (sustained increases from 15 to 120 min following preload consumption, p<0.05). To determine the underlying characteristic of whey protein causing the satiating effect, the effects on satiety of whey protein components (glycomacropeptide, alpha-lactalbumin, or beta-lactoglobulin) and a free amino acid mixture simulating the amino acid composition of the whey protein were compared with that of the intact whey protein. The amino acid composition of whey protein per se appears to be important in the regulation of food intake and the induction of satiety. The individual constituent proteins or whey protein itself did not promote higher satiety than that found based on providing the free amino acids. The absorbed amino acid profile would appear to play an important role in mediating the satiating effect of whey protein.