Only three fundamental mechanisms can underlie the development of obesity: 1) relative
increase in energy intake; 2) relative decrease in energy expenditure; and 3) preferential
partitioning of ingested calories to fat storage. That any one of these defects is sufficient to
cause obesity is demonstrated by the phenotypes of animals produced by specific
transgenic manipulations as follows. 1) Disruption of the 5HT2c serotonin receptor results in
hyperphagia and obesity (1). 2) Defective nonshivering thermogenesis (energy expenditure) …