Why does poor sleep make it harder to lose weight?

Poor sleep disrupts two key hormones: it raises ghrelin, which increases hunger, and lowers leptin, which signals fullness. This combination makes you eat more, particularly craving high-calorie, carbohydrate-rich foods. Sleep deprivation also elevates cortisol, a stress hormone that promotes fat storage, especially around the abdomen. Beyond hormones, poor sleep impairs insulin sensitivity, meaning your body processes glucose less efficiently and is more likely to store it as fat. It also reduces your energy and motivation to exercise, and weakens the prefrontal cortex's ability to regulate impulse control, making it harder to resist unhealthy food choices. Research shows that even with a calorie deficit, sleep-deprived people lose more muscle and less fat compared to well-rested individuals.