I stumbled across this, thought it was interesting...
In a study appearing in the December 1 issue of the Journal of Clinical Investigation, Michael Rosenbaum and colleagues from Columbia University College of Physicians and Surgeons show that body weight is regulated by coordinate metabolic, neuroendocrine, and autonomic systems that act to actually restore fat mass in individuals attempting to maintain their slim new figure. The authors suggest that our bodies interpret the weight-reduced state as one of relative deficiency in the hormone leptin.
To test their hypothesis, the authors administered "replacement" doses of leptin to lean individuals that had recently lost weight as well as to obese individuals. The authors found that most of the metabolic, neuroendocrine, and autonomic changes that oppose the maintenance of a reduced body weight were actually reversed once circulating levels of leptin were restored to levels that were present prior to weight loss. These mechanisms lie at the center of why more than 85% of obese individuals that have lost weight eventually relapse.
These findings suggest that therapeutics directed at the leptin signaling pathway may, pending longer studies, assist in the maintenance of reduced body weight.
full study here:
quoted text taken from here: