Q. What's more important: getting enough sleep or fitting in an early-morning or late-night workout?
A. To change your body composition in the least amount of time, cleaning up your diet and getting seven to eight hours of quality sleep are both essential. Sleep is extremely important for body composition and helps the body and brain restore and rejuvenate in many ways. Plus, sleep (or the lack thereof) affects important hormonal activity tied to appetite and therefore has a direct impact on your ability to lose weight (i.e. body fat).
A 2004 study published online at the Public Library of Science found that people who slept less than seven hours a night ate significantly more and weighed more than those who slept longer. What's more, the more sleep-deprived the person was, the more they ate and the greater their weight gain. These results can be directly attributed to two key appetite-regulating hormones: leptin and ghrelin. Leptin (a hormone secreted by our fat cells) and ghrelin (a hormone secreted in our stomachs) work like a checks and balances system in the body to control your feelings of fullness and hunger. When you don't get enough sleep, your leptin levels drop and your ghrelin levels rise. In other words, you're more likely to crave sugary, high-carb foods (thanks to higher levels of Ghrelin) that have the potential to sabotage your diet.
Growth hormone—which is extremely important for tissue repair, body fat reduction, and healthy immune function—also gets released during sleep.
Now you can see why getting quality sleep is just as important as your workout routine and nutrition. In fact, I would rank sleep and diet as more important than exercise, especially if fat loss (i.e. getting a lean, toned body) is your primary goal.