Meanwhile, the secondary question was set as “is there a difference in the RBP4/visfatin levels between periodontitis patients with obesity and those without obesity and were periodontal healthy?” The random effect model was selected and, in the included two studies, no significant difference in serum RBP4 level [23,26] was found between the groups of obese participants with periodontitis and systematic healthy participants without periodontal diseases (NnP) (Figure 4, SMD = 6.76; 95% CI: −5.34–18.87, p = 0.27). The gene discussed is RBP4; the disease is periodontal disorder.