Effect of Single Oral Coingestion of GABA and Malic Acid on Postprandial GLP-1, Glucose, and Insulin Responses in Healthy Volunteers: A Randomized, Double-Blind, Placebo-Controlled, Crossover Study.

SCOPE: This study examines whether coingestion of γ-aminobutyric acid (GABA) and malic acid (MA) before meals enhances glucagon-like peptide-1 (GLP-1) secretion, and which affects subsequent insulin and glycemic responses in humans. METHODS AND RESULTS: Initially, a murine enteroendocrine STC-1 cell line is used to verify coadministration of GABA and MA synergistically induces GLP-1 secretion. Next, 22 healthy adults are given water (50 mL) containing 400 mg GABA and 400 mg MA (Test), or only 400 mg citric acid (CA) (Placebo) 20 min before meal tolerance test (MTT). Interval blood samples are taken postprandially over 180 min to determine GLP-1, insulin, and glucose responses. By comparison to preload of Placebo, preload of Test significantly increases plasma GLP-1 (total/active) levels (incremental area under the curve by 1.2- and 1.6-fold), respectively. However, there are no significant differences in postprandial blood glucose and insulin. CONCLUSION: Coingestion of GABA and MA before meals enhances postprandial GLP-1 secretion. Future studies should explore optimal dosage regimens to find the efficacy of the mixture on insulin and glycemic response.