Given no enhanced expression of GIP and GLP-1 in duodenal mucosa after 4 weeks following D-LED PBM, alteration of the gut microbiome, dynamic changes in serum GLP-1 and insulin levels, and improved insulin resistance as shown by HOMA-IR from 1 week to 4 weeks in the D-LED PBM group show that duodenal LED PBM may directly affect alterations of the gut microbiome, resulting in lowering serum glucose levels, rather than affecting the duodenal mucosa. This evidence concerns the gene GCG and Insulin resistance.