Abstract
Whey protein is rich in the branched-chain amino acids, L-leucine, L-isoleucine and L-valine. Thus, branched-chain amino acids may, at least in part, mediate the effects of whey to reduce energy intake and/or blood glucose. Notably, 10 g of either L-leucine or L-isoleucine, administered intragastrically before a mixed-nutrient drink, lowered postprandial blood glucose, and intraduodenal infusion of L-leucine (at a rate of 0.45 kcal/min, total: 9.9 g) lowered fasting blood glucose and reduced energy intake from a subsequent meal. Whether L-valine affects energy intake, and the gastrointestinal functions involved in the regulation of energy intake, as well as blood glucose, in humans, is currently unknown. We investigated the effects of intraduodenally administered L-valine on antropyloroduodenal pressures, plasma cholecystokinin, blood glucose and energy intake. Twelve healthy lean men (age: 29 ± 2 years, BMI: 22.5 ± 0.7 kg/m2) were studied on 3 separate occasions in randomised, double-blind order. Antropyloroduodenal pressures, plasma cholecystokinin, blood glucose, appetite perceptions and gastrointestinal symptoms were measured during 90-min intraduodenal infusions of L-valine at 0.15 kcal/min (total: 3.3 g) or 0.45 kcal/min (total: 9.9 g), or 0.9% saline (control). Energy intake from a buffet-meal immediately after the infusions was quantified. L-valine did not affect antral, pyloric (mean number; control: 14 ± 5; L-Val-0.15: 21 ± 9; L-Val-0.45: 11 ± 4), or duodenal pressures, plasma cholecystokinin (mean concentration, pmol/L; control: 3.1 ± 0.3; L-Val-0.15: 3.2 ± 0.3; L-Val-0.45: 3.0 ± 0.3), blood glucose, appetite perceptions, symptoms or energy intake (kcal; control: 1040 ± 73; L-Val-0.15: 1040 ± 81; L-Val-0.45: 1056 ± 100), at either load (p > 0.05 for all). In conclusion, intraduodenal infusion of L-valine, at loads that are moderately (3.3 g) or substantially (9.9 g) above World Health Organization valine requirement recommendations, does not appear to have energy intake- or blood glucose-lowering effects.
Highlights
High-protein diets, when compared with diets high in carbohydrate or fat, appear to have more potent effects to decrease appetite and body weight and improve glycaemic control in obese people with and without type 2 diabetes [1,2,3,4]
We have investigated the effects of the branched-chain amino acids (BCAAs), L-valine, which is abundant in whey protein, to elucidate whether L-valine, like L-leucine and L-isoleucine, has potent effects to reduce energy intake and/or blood glucose and to modulate key underlying GI functions
Our study indicates that L-valine, when administered intraduodenally at loads of 0.15 kcal/min or 0.45 kcal/min for
Summary
High-protein diets, when compared with diets high in carbohydrate or fat, appear to have more potent effects to decrease appetite and body weight and improve glycaemic control in obese people with and without type 2 diabetes [1,2,3,4]. In response to intraduodenal administration of whey protein, we have observed direct correlations between plasma concentrations of these amino acids with plasma concentrations of GLP-1 and insulin, and an inverse correlation with energy intake [14], supporting the concept that these amino acids, at least in part, mediate the effects of whey to reduce energy intake and/or blood glucose.
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