Increasing a large variety of dietary fiber can significantly improve insulin secretion and insulin sensitivity in patients with T2DM by altering the structure of the microbiota; at the strain level, a group of “short-chain fatty acid”-producing bacteria, which are conducive to increasing insulin secretion and insulin sensitivity, can be regarded as “ecological functional groups” necessary for the restoration and maintenance of human health. Here, INS is linked to type 2 diabetes mellitus.