Are obese people resistant to leptin?

Yes: Although leptin is a circulating signal that reduces appetite, obese individuals generally exhibit an unusually high circulating concentration of leptin. These people are said to be resistant to the effects of leptin, in much the same way that people with type 2 diabetes are resistant to the effects of insulin.

Yes: Leptin resistance can result from excessive stress. This stress can be immune system stress, hormonal stress or nervous system stress. The excess stress produces chemicals called "cytokines" which then injure your hypothalamus and impair the hypothalamic response to leptin. Hence the leptin resistance. This explains why so many obese people have trouble losing weight even if they do not eat much.