GCG and type 2 diabetes mellitus: Consistent with these findings, a pivotal randomized study demonstrated that a high-fiber diet in patients suffering from type-2 diabetes mellitus significantly affects GM fermentation of carbohydrates, promoting a wider diversity and abundance of butyrate-producing bacteria and improving hemoglobin A1c levels, partly through increased glucagon-like peptide-1 (GLP-1) production [35].