Effect of L-Tryptophan and L-Leucine on Gut Hormone Secretion, Appetite Feelings and Gastric Emptying Rates in Lean and Non-Diabetic Obese Participants: A Randomized, Double-Blind, Parallel-Group Trial

Background/Objectives

Gut hormones such as cholecystokinin (CCK)
and glucagon-like peptide-1 (GLP-1) play a role as satiation factors. Strategies
to enhance satiation peptide secretion could provide a therapeutic approach for
obesity. Carbohydrates and lipids have been extensively investigated in
relation to peptide release. In contrast, the role of proteins or amino acids
is less clear. Our aim was to compare the effects of the amino acids
L-tryptophan (L-trp) and L-leucine (L-leu) separately on gastric emptying and
gut peptide secretion.

Participants/Methods

The study was conducted as a randomized (balanced), double-blind, parallel-group trial. A total of 10 lean and 10 non-diabetic obese
participants were included. Participants
received intragastric loads of L-trp (0.52 g and 1.56 g)
and L-leu (1.56 g), dissolved in 300 mL tap water; 75 g
glucose and 300 mL tap water served as control treatments.

Results

Results of the study are: i) L-trp at
the higher dose stimulates CCK release (p=0.0018), and induces a significant
retardation in gastric emptying (p=0.0033); ii) L-trp at the higher dose
induced a small increase in GLP-1 secretion (p=0.0257); iii) neither of the amino
acids modulated subjective appetite feelings; and iv) the two amino acids did
not alter insulin or glucose concentrations.

Conclusions

L-trp is a luminal
regulator of CCK release with effects on gastric emptying, an effect that could
be mediated by CCK. L-trp’s effect on GLP-1 secretion is only minor. At the
doses given, the two amino acids did not affect subjective appetite feelings.