Food have leptin

Leptin acts on receptors in the hypothalamus of the brain where it inhibits appetite by (1) counteracting the effects of neuropeptide Y (a potent feeding stimulant secreted by cells in the gut and in the hypothalamus); (2) counteracting the effects of anandamide (another potent feeding stimulant that binds to the same receptors as THC, the active ingredient of marijuana); and (3) promoting the synthesis of α-MSH, an appetite suppressant.

Leptin hormone role of in obesity and food intake by Ray Sahelian, M.D. Leptin is a hormone secreted from adipocytes (fat cells) and functions to suppress appetite and increase energy expenditure. Leptin is a proinflammatory cytokine. In contrast, ghrelin, a protein known to trigger feeling of hunger, increases during periods of fasting and decreases after a meal.

It's a grim statistic: Most people who go on a diet and lose weight end up regaining that weight within a year. Doesn't sound too promising. Why does this happen? Well, there are many reasons.