(6) T2D is polygenic and multifactorial, and there are a variety of possible genetic (> 80 genetic susceptibility loci have been identified [76], e.g., TCF7L2, PPARG), environmental (e.g., air pollution by nitrogen dioxide, PM2.5, and PM10 [77]), nutritional (e.g., dietary fiber, fat intake [78]), lifestyle (e.g., physical inactivity [79]) and sociodemographic (e.g., age, ethnicity, education [80]) risk factors involved in the etiology of this disease. This evidence concerns the gene TCF7L2 and type 2 diabetes mellitus.