Sleep is hugely important in helping us stay healthy and trim. Log fewer than seven hours and you invite illness into your life. Studies link sleep deficits with higher risks of obesity and heart disease. If you don't sleep soundly, go to bed 15 minutes later the next night, says Men's Health sleep medicine advisor W. Christopher Winter, M.D. If you sleep great but feel groggy in the a.m., go to bed 15 minutes earlier. Repeat to find your ideal amount.