The aim of this study was to identify regulatory T cell (Treg) subsets residing in adipose tissue, demonstrate their immunosuppressive functions, and assess the possible role of Sirt1 in their function in overweight subjects.Fat samples were obtained by lipoaspiration from healthy overweight (n = 15) and normoweight (n = 11) subjects. We obtained the stromal vascular fraction and then isolated the mononuclear cells by Ficoll-Hypaque sedimentation. The Treg subsets were analyzed by flow cytometry, the expression of Sirt1 and Foxp3 was detected by western blot, and peroxisome proliferator-activated receptor gamma (PPAR-γ) expression was evaluated by qPCR.We detected low numbers of Treg cell subsets displaying the phenotypes CD4+CD25-Foxp3+, CD8+CD25-Foxp3+, and CD4+CD39+Foxp3+ associated with increased body mass index in overweight subjects. We found lower levels of mRNA SIRT1 expression in adipocytes from overweight subjects than in those from normoweight subjects. In contrast, increased amounts of the Sirt1 and Foxp3 proteins in adipose tissue mononuclear cells from overweight subjects were observed. The immunosuppressive function of CD4+CD25+ Treg cells is higher in cells from obese subject than in those from normoweight subject.Low levels of Treg subsets in overweight subjects with a high percentage of inhibition of proliferation could be related to high levels of the Foxp3 protein. Likewise, the low expression of SIRT1 and PPAR-γ mRNA levels and increased concentration of Sirt1 proteins allows adipose tissue mononuclear cells to respond to stimuli dependent on adenosine receptors and sirtuin pathways.