Research suggests reduced hours of sleep have negative effects on metabolism. In adults, sleeping four hours a night, compared with 10 hours a night, appears to increase hunger and appetite — in particular for sweet foods. There appears to be a strong link between lack of sleep and obesity. One explanation might be that sleep duration affects hormones regulating hunger — ghrelin, and leptin. Another contributing factor might be that lack of sleep leads to fatigue and results in less physical activity. So now you have another reason to get a good night's sleep.