Cell Wall-Formed Dietary Fiber in Tartary Buckwheat Governs Selective Enrichment of Phytochemicals to Enhanced Postprandial GLP-1 Response

Glucagon-like peptide-1 (GLP-1) is well-known for its biological functions in glucose homeostasis which aligns closely with the antidiabetic function of whole grain foods (WGFs). Although postprandial GLP-1 responses to WGF have been extensively studied, the influence of cell wall-formed dietary fiber (CW-DF), as the main functional component of WGFs, on the GLP-1 response remains poorly understood. Here, Tartary buckwheat flour fractions with different particle sizes (small particle size (SF: 0.2 mm), middle particle size (MF: 0.6 mm), and large particle size (BF: 0.9 mm)), reflecting different degrees of cell wall integrity, were used to investigate how particle size modulates GLP-1 secretion. The in vivo mouse study showed that intact endosperm cells from Tartary buckwheat grains significantly increased the postprandial GLP-1 response. Further study demonstrated that only the hydrolysate from BF augmented GLP-1 secretion from enteroendocrine STC-1 L-cells, which is all positively correlated with the selectively enriched phytochemicals in BF particles (ononin, ginkgolide C, pristimerin, and pentadecanoic acid). Significant correlations between particle size, phytochemical profiles and GLP-1 release demonstrated that the integrity of CW-DF is essential to the nutritional properties of WGFs. Molecular docking simulations suggested putative interactions between phytochemicals and bitter taste receptors in GLP-1 secretion. Thus, cell wall integrity is a pivotal regulator of the health benefits of WGFs, offering a mechanistic rationale for minimal processing to harness the health benefits of WGFs through targeted endogenous GLP-1 production.