The mechanisms underlying different types of obesity have been gradually clarified. Animal models with hypothalamic, genetic or dietary obesity have been examined with a feedback model. Four common final pathways are involved in this model. One of these final common pathways is the sympathetic nervous system. Most Obesities kNown Are Low In Sympathetic Activity states the MONA LISA Hypothesis. A second common pathway is the endocrine system involving adrenal glucocorticosteroids. The third common pathway is hyperphagia. Although not essential for most obesities, hyperphagia may be essential in animals with injury to the hypothalamic paraventricular nucleus. The final pathway is reduced physical activity. The tonic activity of these systems and their response to changes in the diet affect nutrient partitioning between fat and protein. This framework has been used to review genetic obesity, hypothalamic obesity and dietary obesity.