Hormones in our body influence whether we eat. The main hormones that increase hunger( they tell us : eat! eat!) are ghrelin and neuropeptide Y. Ghrelin is produced in the stomach. Neuropeptide Y is produced in the part of the brain called hypothalamus.
The main hormone that cause satiety is leptin (it tells us : do not eat!) . Leptin is produced by fat cells. Injection of leptin to obese people did not produce results.