Effects of whole grain intake on glucagon-like peptide 1 and glucose-dependent insulinotropic peptide: a systematic review and meta-analysis

Abstract

Context: Whole grain intake may control help glycemia and reduce food intake by affecting the secretion of glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP).

Objective: This systematic review and meta-analysis aimed to assess the postprandial and long-term effects of whole grains on GLP-1 and GIP levels.

Data sources: PubMed, Web of Science, and Scopus online databases were searched systematically to identify relevant randomized clinical trials (RCTs) published up to April 2021.

Study selection: RCTs that evaluated the effects of whole grains, compared with refined grains, on the postprandial area under the curve (AUC) value, the postprandial serum concentration of incretins from 0 to 180 minutes, or the fasting level of incretins after at least 14 days of intervention were included.

Results: Nineteen studies were included in the meta-analysis. The results showed that acute intake of whole grains could not significantly change the AUC value of GLP-1 or GIP. However, the AUC value of GIP was reduced more significantly in (1) unhealthy participants (standard mean difference [SMD] -1.08; 95%CI, -2.07 to -0.10; I2 = 75.9%) compared with healthy participants, and (2) those with a baseline fasting blood glucose of ≥99 mg/dL (SMD -0.71; 95%CI, -1.30 to -0.11; I2 = 74.4%) compared with those with a baseline value of < 99 mg/dL. On the other hand, the results of time-response evaluation during 0 to 180 minutes after the intake of test meals showed that serum concentrations of GIP decreased significantly from 0 to 30 minutes (coefficient = -44.72; P = 0.005), but increased from 60 to 180 minutes (coefficient = 27.03; P = 0.005). However, long-term studies found no significant effects of whole grains on fasting concentrations of GLP-1 or GIP.

Conclusion: Whole grain intake did not affect postprandial levels of GLP-1 but enhanced postprandial levels of GIP from 60 to 180 minutes. Further high-quality trials are required to assess the long-term effects of whole grain intake on serum levels of incretins.

Systematic review registration: PROSPERO registration no. CRD42021256695.

Keywords: glucagon-like peptide-1; glucose-dependent insulinotropic peptide; whole grains.