Abstract
This study determined the effects of increasing loads of whey protein on plasma amino acid (AA) concentrations, and their relationships with gastric emptying, blood glucose- and appetite-regulatory hormones, blood glucose and energy intake. Eighteen healthy lean men participated in a double-blinded study, in which they consumed, on 3 separate occasions, in randomised order, 450-mL drinks containing either 30 g (L) or 70 g (H) of pure whey protein isolate, or control with 0 g of protein (C). Gastric emptying, serum concentrations of AAs, ghrelin, cholecystokinin (CCK), glucagon-like-peptide 1 (GLP-1), insulin, glucagon and blood glucose were measured before and after the drinks over 180 min. Then energy intake was quantified. All AAs were increased, and 7/20 AAs were increased more by H than L. Incremental areas under the curve (iAUC0–180 min) for CCK, GLP-1, insulin and glucagon were correlated positively with iAUCs of 19/20 AAs (p < 0.05). The strongest correlations were with the branched-chain AAs as well as lysine, tyrosine, methionine, tryptophan, and aspartic acid (all R2 > 0.52, p < 0.05). Blood glucose did not correlate with any AA (all p > 0.05). Ghrelin and energy intake correlated inversely, but only weakly, with 15/20 AAs (all R2 < 0.34, p < 0.05). There is a strong relationship between gluco-regulatory hormones with a number of (predominantly essential) AAs. However, the factors mediating the effects of protein on blood glucose and energy intake are likely to be multifactorial.
Highlights
High-protein diets, including those that incorporate about 2–3 serves of dairy protein, are effective in the management of obesity and associated cardio-metabolic conditions [1,2,3,4,5]
amino acid (AA) within foods containing an intact or hydrolysed protein and how they collectively influence the modulation of glucose- and appetite-regulatory hormones, as well as energy intake
We have established for the first time that 450 mL, isoosmolar test drinks containing either 30 or 70 g of pure protein substantially increased the plasma AA responses of only 7 of the 20 AAs in a load-of-protein dependent manner
Summary
High-protein diets, including those that incorporate about 2–3 serves of dairy protein, are effective in the management of obesity and associated cardio-metabolic conditions [1,2,3,4,5]. Several studies have reported dose-dependent effects of whey protein on concentrations of blood glucose- and appetite-regulatory hormones, including cholecystokinin (CCK), glucagon-like peptide-1 (GLP-1), insulin and glucagon [10,11,12,13,14,15]. In healthy individuals, whey protein in loads of 4.5–18 g (in a drink containing 25 g glucose) dose-dependently lowered postprandial glycaemia and increased insulin, with a minimum of 9 g required for a significant effect [8]. There is no information about the relationships between the release of specific AAs with glucose- and appetite-regulatory hormones, gastric emptying and energy intake responses following the consumption of protein-enriched drinks
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