L-glutamine triggers the release of glucagon-like peptide-1 (GLP-1) from L cells in vitro, and when taken before a meal, it reduces postprandial glycemia and increases circulating insulin and GLP-1 in patients with type 2 diabetes (T2D). Our objective was to investigate the effect of orally administered L-glutamine compared with glutamine-depleted whole protein on insulin response in well-controlled T2D patients.
In a randomized trial with a crossover design, T2D patients (n = 10, 6 men) aged 65.1 ± 5.8 yr with glycosylated hemoglobin (HbA1c) 6.6% ± 0.7% (48 ± 8 mmol/mol) received oral l-glutamine (25 g), protein (25 g), or water followed by an intravenous glucose bolus (0. 3 g/kg) and hyperglycemic glucose clamp for 2 h. The glucose response of the glucose bolus was determined by the glucose concentration in the blood. Blood was drawn frequently for analyses of glucose, serum insulin, and plasma total and active GLP-1 and area under the curve of calculated glucose, insulin, total, and active GLP-1 excursions.
Treatments were tested 1-2 weeks apart. Both L-glutamine and protein increased insulin response in the first phase (p ≤ 0.02). Protein (p = 0.05), but not L-glutamine (p = 0.2), increased insulin response in the second phase. Total GLP-1 was increased by both L-glutamine and protein (p ≤ 0.02). We conclude that oral L-glutamine and total protein are similarly effective in restoring first-phase insulin response in T2D patients.
