Obesity and type 2 diabetes mellitus (T2D) are two major public health problems that have motivated the scientific community to investigate the high contribution of genetic factors to these disorders. The peroxisome proliferator activated by gamma 2 (PPARg2) plays an important role in the lipid metabolism. Since PPARg2 is expressed mainly in adipose tissue, a moderate reduction of its activity influences the sensitivity to insulin, diabetes, and other metabolic parameters. The present study aims to contribute to the elucidation of the impact of the Pro12Ala polymorphism associated with T2D and obesity through a meta-analysis study of the literature that included approximately 11500 individuals, from which 3870 were obese and 7625 were diabetic. Statistical evidence supports protective effect in T2D of polymorphism Pro12Ala of PPARg2 (OR = 0.702 with 95% CI: 0.622; 0.791, P <0.01). Conversely the same polymorphism Pro12Ala of PPARg2 seems to favor obesity since 1.196 more chance than non obese was found (OR=1.196 with 95% CI: 1.009; 1.417, P < 0.004). Our results suggest that Pro12Ala polymorphism enhances both adipogenic and antidiabetogenic physiological role of PPARg. Does Pro12Ala polymorphism represent an evolutionary step towards the stabilization of the molecular function of PPARg transcription factor signaling pathway?