You didnt get a good nights sleepIf you’re chronically sleep deprived, dont be surprised if you gain a few pounds without eating a morsel of extra food. A lack of sleep can cause several metabolic problems, says nutritionist Seth Santoro. It can cause you to burn fewer calories, lack appetite control and experience an increase in cortisol levels, which stores fat. Lack of sufficient sleep which experts say is 7 to 9 hours a night for most people also leads to impaired glucose tolerance, a.k.a. your body’s ability to utilize sugar for fuel.