Intraduodenal Administration of L-Valine Has No Effect on Antropyloroduodenal Pressures, Plasma Cholecystokinin Concentrations or Energy Intake in Healthy, Lean Men

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.

Keywords: appetite regulation; branched-chain amino acids; glycaemia; gut hormones; gut motility; human.

Figure 1

Energy intake from a buffet meal after 90-min intraduodenal infusions of control, or L-valine at 0.15 kcal/min (“L-Val-0.15”) or 0.45 kcal/min (“L-Val-0.45”). One-way ANOVA was used to analyse the data. Statistical significance was accepted at p < 0.05. Data are means ± SEMs, n = 12.

Figure 2

Scores for hunger (A), fullness (B), desire to eat (C), prospective consumption (D), bloating (E) and nausea (F) during 90-min intraduodenal infusions of L-valine at 0.15 kcal/min (“L-Val-0.15”) or 0.45 kcal/min (“L-Val-0.45”), or control. Repeated-measures two-factor ANOVA, with treatment and time as factors, was used to analyse the data. Post-hoc comparisons, adjusted for multiple comparisons by Bonferroni correction, were used to determine significant differences between treatments if ANOVAs were significant. Statistical significance was accepted at p < 0.05. Data are means ± SEMs, n = 12.

Figure 3

Plasma CCK (A) and blood glucose (B) concentrations during 90-min intraduodenal infusions of L-valine at 0.15 kcal/min (“L-Val-0.15”) or 0.45 kcal/min (“L-Val-0.45”), or control. Repeated-measures two-factor ANOVA, with treatment and time as factors, was used to analyse the data. Post-hoc comparisons, adjusted for multiple comparisons by Bonferroni correction, were used to determine significant differences between treatments if ANOVAs were significant. Statistical significance was accepted at p < 0.05. Data are means ± SEMs, n = 11 for CCK (due to technical difficulties with blood sampling), n = 12 for glucose.