5 Obesity in Polycystic Ovary Syndrome Carlos Moran 1, 3 , Monica Arriaga 1 , Gustavo Rodriguez 2 and Segundo Moran 3 1 Direction of Health Research and Training, Medical Unit of High Specialty, Gynecology and Obstetrics Hospital No. 4 Luis Castelazo Ayala, 2 General Hospital of Zone No. 8 3 Health Research Council, Mexican Institute of Social Security, Mexico City, Mexico 1. Introduction Polycystic ovary syndrome (PCOS) is an endocrine and metabolic heterogeneous disorder, with a likely genetic origin, influenced by environmental factors such as nutrition and physical activity. The main clinical features of PCOS are related to hyperandrogenism, such as hirsutism, acne and menstrual disorders (Moran et al., 1994; Azziz, et al., 2004; Carmina et al., 2006). PCOS is also associated with overweight or obesity (Azziz, et al., 2004), mainly abdominal adiposity (Moran et al., 1999). The etiology of PCOS is unknown. The genetic origin is based on the observation that PCOS is more frequent among the sisters and mothers of these patients (Lunde et al., 1989; Govind et al., 1999). Moreover, in a study done with twins, a higher correlation in the presence of PCOS is observed more in monozygotic than in dizygotic (Vink et al., 2006). Multiple genes related to the production of androgen, the function of the gonadotropin, the action of insulin and the regulation of energy have been evaluated. Although associations of some genes with clinical disorders of PCOS have been found, in specific regions and determined polymorphisms, the findings of studies and in different populations have not been consistent (Wood et al., 2003). The hypothesis of the origin of PCOS by environmental factors is based on the beneficial results observed by weight loss, and the worsening with increasing weight in these patients. The interaction of environmental factors of PCOS in women affected starts from their prenatal and postnatal life (Abbott et al., 2002). Food habits and lifestyle are also factors in the presentation and the development of PCOS. The influence of the environmental component of PCOS and its interaction with the genetic component has been less studied. Obesity plays an important role in the pathogenesis of PCOS, and the majority of patients with PCOS are overweight or obese; however, these disorders are not considered as diagnostic criteria for PCOS, since not all obese women present hyperandrogenism. 2. Diagnosis The major criteria of PCOS, proposed in the consensus of the National Institutes of Health in Bethesda, M.D., were (in order of importance): a) hyperandrogenism and/or hyperandrogenemia, b) oligoovulation, c) exclusion of other known disorders, and d) possibly