Why does poor sleep make you gain weight over time?

Poor sleep disrupts the hormones that regulate hunger and appetite. Specifically, it raises ghrelin (the hormone that makes you feel hungry) and lowers leptin (the hormone that signals fullness), so you end up eating more than you need. Sleep-deprived people also tend to crave high-calorie, high-carbohydrate foods because the brain's reward centers become more reactive when tired. Beyond appetite, poor sleep raises cortisol levels, which promotes fat storage particularly around the abdomen. It also impairs insulin sensitivity, meaning your body handles blood sugar less efficiently and is more likely to store excess glucose as fat. On top of that, fatigue reduces physical activity and motivation to exercise, compounding the caloric imbalance over time.