Lack of sleep makes you fatter and even leads to muscle loss, regardless of diet. Check this out.
Since when did not getting enough sleep become a bragging right? "Dude, I only sleep 5 hours a night!" Congratulations. How many times can you hit yourself in the naughty bits with a hammer before training?
Like getting inadequate sleep, it doesn't make you tough, but it certainly affects your efforts in the gym. While you may be able to "function just fine" on a few hours of sleep, doing so still short changes your body composition goals.
In one study, the group of people that slept 8.5 hours a night lost more fat than the group that slept a mere 5.5 hours a night. Additionally, the group that slept less lost significantly more muscle (60%!) than the group that got the full 8.5 hours. Both groups ate roughly the same amount of calories per day. Just another reason why body comp is more complicated than just "calories in versus calories out."
Where do you think your recovery really comes from? Babies tend to do two things after they are born – eat and sleep a lot. Why? Because to grow the body requires a tremendous amount of rest. So if you aren't getting an adequate amount of sleep, then when are you giving your body the extra time it needs for this process to take place?
Getting the mind and body to relax at night can be a problem. Make sure your circadian rhythm, which is established via dark and light, is functioning normally. When it's dark, your body releases more melatonin. When it's light, it reduces melatonin output and increases appropriate amounts of more excitatory hormones.
The light you expose yourself to can upset the release of natural melatonin by the body, and delay your restful state for sleep. Reduce TV, laptop, and cell phone use in the evenings, unless you're up late reading my articles, and open up the curtains so that your body is awakened by natural sunlight each morning. Morning sunlight exposure will help get your circadian rhythm back in order.