What’s Sleep Got to Do With It?
There’s good evidence from short-term randomized controlled trials that if you restrict a person’s sleep, they will eat more calories, even though they actually may burn a few more calories as well. You burn fewer calories when you’re asleep and more when you’re awake. However, this additional calorie burn doesn’t make up for the higher calorie intake. People will eat about 300 extra calories a day when sleep deprived which is quite substantial. What is clear from the long-term observational studies is that there is, in fact, a strong association between insufficient sleep and weight gain over time.
When you put someone in an fMRI (functional magnetic resonance imaging) machine you can look at their brain activity—if they haven’t slept enough, their brain acts like they’re starving. That same response is evident in the brain of someone who has recently started a diet and their brain has initiated a starvation response. They may be feeling hungry, or more tempted by food, maybe they’re feeling a little bit sluggish and cold, those same responses or at least very similar ones occur in the brains of people who are sleep restricted. Inadequate sleep activates some of these same circuits that cause us to be more seduced by food and require more food to feel full. That’s one way it can work.
Sleep restriction also seems to significantly impair your ability to have sound judgments. Also, you often develop what’s called an “optimism bias” which means you’re not very sensitive to the downsides of making a decision. Instead, you are paying more attention to the potential upsides. How that can play out with food is that normally you might say, “Hey, well, you know this donut looks tasty, but I know it’s not good for me. Therefore I’m not going to eat it.” However, if you haven’t slept enough, you justify your choice to eat it because you “need the energy,” or because you’re apathetic towards your goals and you don’t think you’ll make it without a little sugar pick-me-up.