That title seems too good to be true doesn't it? Sleeping to lose weight. How dreamy! ;) Sleep can help you lose weight by allowing your body proper time to rest and repair itself. Your hormones balance, your stress levels lower and your body can make itself more efficient at using energy.
Cortisol is one of our body's stress hormones. It's released from your adrenal glands and plays an important role in how our body uses carbohydrates/sugar for energy. When you're in a life threatening situation, cortisol can make your body release stores of energy for immediate use and sharpen your brain. However, if cortisol remains high because of chronic stress it can contribute to insulin resistance, weight gain, high blood pressure, mental illness and more. When you are sleep deprived your body can release more cortisol than normal to help you stay alert and awake to function during the day. Having elevated cortisol levels works against your weight loss efforts.
Hunger hormones are also balanced when you sleep. Two of the big bosses of hunger and satiety are ghrelin (increases hunger) and leptin (increases satiety). When you sleep sufficiently these hormones are balanced. If you're sleep deprived you'll have more ghrelin and less leptin causing you to overeat and gain weight.
If you've been trying to lose weight but you're not sleeping enough you're working against yourself. Sleep 7-9 hours of sleep and not only will you improve you mental capacity to make healthy choices throughout your day, you'll also optimize your body's ability to lose weight.