LEP and obesity due to melanocortin 4 receptor deficiency: A scheme network indicating the correlations among the key metabolites, the strain contributors to the key metabolites, and the three obesity-relevant clinical parameters (BMI, leptin, and adiponectin) was then drawn, as shown in Figure 1D. As shown, the three folates, folate (fol), tetrahydrofolate (thf), and 5 methyltetrahydrofolic acid (5mthf), that negatively correlated with BMI are mainly produced by strains of Bifidobacterium longum, a category of well-established and multifunctional probiotics (Figure 1D).