In general, the obese have no shortage of leptin (given that leptin is produced by fat cells, if anything they tend to have more).
The thinner you become, the lower your leptin levels droop, and the more food it takes to satisfy your appetite.
However, when leptin levels drop, hunger signals go through the roof, often resulting in overeating.
a protein produced by fat cells and involved in regulating food intake and fat storage in the body
1995-2000; < Gk leptos thin