Whey protein supplementation improves postprandial glycemia in persons with type 2 diabetes mellitus: A systematic review and meta-analysis of randomized controlled trials.

Whey protein (WP) can increase insulin secretion, produce an incretin effect, delay gastric emptying, and regulate appetite, resulting in improved glycemic control. We hypothesized that WP supplementation is associated with postprandial glycemia regulation in persons with type 2 diabetes mellitus (T2DM) and conducted a quantitative meta-analysis of randomized controlled trials (RCTs) to test this hypothesis. We searched PubMed, Embase, Cochrane Library, Scopus databases, and the ClinicalTrials.gov registry for relevant RCTs published before March 2022. We assessed the pooled effects using a random-effects model on glucose and insulin levels at 60 and 120 minutes, total glucagon-like peptide-1 (tGLP-1) at 30 and 60 minutes, and the incremental area under the curve (iAUC) of glucose, insulin, tGLP-1, and glucose-dependent insulinotropic polypeptide. Five RCTs involving 134 persons were included. Postprandial glycemia was significantly lower at 60 minutes (weighted mean difference: -2.67 mmol/L; 95% confidence interval, -3.62 to -1.72 mmol/L) and 120 minutes (-1.59 mmol/L; -2.91 to -0.28 mmol/L) in WP group than in placebo group. The iAUC of insulin was significantly higher in WP group (24.66 nmol/L × min, 1.65-47.66 nmol/L × min) than in placebo group. Although other results favored the WP group, differences between the groups were not statistically significant. The present study showed that premeal WP supplementation is beneficial for postprandial glycemia in persons with mild or well-controlled T2DM without substantial adverse effects. However, the level of certainty of current evidence is not high enough. Further larger and well-designed clinical trials are warranted for evaluating optimal dose and long-term effects of WP supplementation.