Sleep deprivation can cause an increase in your appetite and fat round your middle. A decrease in insulin (the hormone released when you take sugar) increases your appetite. Research suggests that less than 7 hours quality sleep per night can result in an increase in weight Leptin plays a key role in regulating energy intake and expenditure including appetite and metabolism. Its effect on the hypothalamus in the brain controls the feelings of being full after eating. Research carried out with mice using leptin did produce a dramatic reduction in weight but unfortunately Leptin may cause adverse effects on blood pressure and sodium metabolism. The best way to ensure adequate leptin levels is to have good quality sleep. Low vitamin D levels can also be a factor in increased weight.