Several mechanisms have been proposed to explain protein-induced satiety, including increased energy expenditure, changes in the concentrations of “satiety” hormones, and changes in central pathways (3,7-9,26).
An increase in energy expenditure, through increased thermogenesis, has been proposed to induce satiety (7,9,18,19,26,27). Since dietary protein stimulates diet-induced thermogenesis to a greater extent than do other macronutrients, it is reasonable to include this as a potential “satiety” mechanism of action. While a relationship between energy expenditure and protein-induced satiety has been observed, most of these findings result from longer-term studies containing fairly large quantities of dietary protein (5,9,19).
Satiety may also be mediated through protein-induced increases in the concentrations of appetite-suppressing hormones such as glucagon-like peptide-1 (GLP-1), cholecystokinin (CCK), and peptide tyrosine tyrosine (PYY) and/or decreases in appetite-stimulating hormones such as ghrelin (9,26,28). However, the effect of increased protein intake on changes in hormone levels is inconsistent (4,9,16,29). For example, a change in hormone levels after a high protein preload occurred in one short-term study (29), whereas in another short-term study no differences in ghrelin, GLP-1, and PYY responses between the high protein and adequate protein intake appeared (16).
Protein-induced changes in “satiety” hormones appear to be related to the amount and type of protein consumed and are mainly involved in short-term protein-induced satiety (5,26,28,30). Whether protein-induced changes in “satiety” hormones are related to satiety ratings or energy intake remains to be conclusively established. Some researchers have shown that while increased intake of specific proteins results in significant differences in hormone responses, these are not necessarily related to satiety ratings or energy intake (31-33).
Along these lines, higher protein diets may also activate specific regions of the brain involved in the central regulation of food intake (26). A study in laboratory rats showed that high protein meals activated satiety-related neuronal pathways in the brainstem and hypothalamus (34).
Dairy proteins – casein and whey – as part of a high protein diet have been shown to increase satiety. However, more research is needed to determine the optimal amount of these proteins and/or servings of dairy foods to reduce energy intake.
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