You do lose weight while you sleep, but this weight loss is primarily from burning calories at a low metabolic rate and from losing water through sweating and breathing. Your body continues to burn calories during sleep to support basic functions like breathing and circulation. On average, a person burns roughly 200 to 400 calories during a full night's sleep depending on body weight. Additionally, water loss through sweat and exhaled breath also contributes to weight loss overnight, which can amount to around 1-2 pounds by morning. However, this is mostly water weight, not fat loss. Sleep itself does not cause fat loss directly, but getting adequate, quality sleep supports weight loss efforts by regulating metabolism and appetite hormones. Poor sleep is linked to increased hunger hormones, poorer food choices, and reduced fat loss during dieting. Thus, good sleep helps promote fat loss over time by supporting metabolic health and reducing overeating. In summary, weight loss during sleep is due to a combination of calorie burning at rest and water loss. While sleep alone is not a weight loss strategy, it is essential for healthy metabolism and successful weight management.