Friedman presented an overview of the hormone leptin and its role in maintaining weight. His research showed that fat itself is an endocrine tissue that secretes leptin, which, in turn, affects appetite and metabolism. Simply put, when fat is lost, levels of leptin fall, and appetite is increased. Your body is attempting to replace fat and restore the “balance” of leptin. When levels of leptin rise above a certain point, appetite is suppressed. In this way, our bodies seek out some homeostasis, and it’s likely that we have some genetic predisposition to fat, and therefore leptin, levels.