The 11 potential confounders, including sex, obesity (BMI ≥ 27 kg/m2), use of various antidiabetic medications, and statin, were poorly correlated with plasma cytokine levels of IFN-γ, IL-17A, IL-17F, IL-2, IL-10, IL-22, TNF-α and TGF-β, and the model performance improved after adding the 6 selected genera into the linear regression model (Additional file 1: Tables S9 and S10). Here, IL17F is linked to obesity due to melanocortin 4 receptor deficiency.