Ultimately, this review found that gut flora such as Akkermansia and Verrucomicrobia, serum albumin levels, inflammatory mediators such as IFN-γ and CRP, leukocyte telomere length, protein, diabetic retinopathy, thyroid dysfunction, obesity, coffee intake, and sleep were all causally associated with the development of DN (Figure 6). Here, IFNG is linked to obesity due to melanocortin 4 receptor deficiency.