NOS3 and obesity due to melanocortin 4 receptor deficiency: BMI can be regarded as a convenient proxy for energy intake and consumption, as demonstrated by the association between dietary fat and obesity [29], which was represented in a study of the interaction between a polymorphism in the nitric oxide synthase 3 (NOS3) gene and BMI on the risk of type 2 diabetes [30] and in other studies [18].