If you've ever finished a full meal and still felt hungry twenty minutes later, leptin is probably part of the story. Leptin is a hormone produced by your fat cells, and its job is simple: tell your brain that you have enough stored energy so you can stop eating.
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​The problem is that this signal doesn't always get through. With excess body fat, the brain can actually become resistant to leptin — a condition appropriately called "leptin resistance." Your fat cells are shouting "we're full," but your hypothalamus stops listening. The result is a frustrating paradox: the more fat tissue you carry, the higher your leptin levels tend to be, yet the hungrier you can feel.
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​Sleep plays a bigger role here than most people expect. Adequate, quality sleep helps keep leptin signaling working properly, while poor sleep lowers leptin and drives hunger up — one of several reasons a bad night's sleep so often shows up as extra snacking the next day.
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​The practical takeaway: weight loss isn't purely a willpower problem. If your hunger doesn't match your intake, leptin resistance may be part of what's going on, and it responds to the same fundamentals — better sleep, gradual fat loss, and consistent eating patterns — rather than white-knuckling through hunger.