The resolution that always gets overlooked, the thing that’s going to make your fitness or weight loss goal, that much easier is sleep. The science behind sleep has been getting a lot more attention in the last few years because we keep on finding all these benefits of consistent sleep.
How Sleep can Impact Weight loss and Fitness
You might think that by being awake, your heart rate is higher and so you’re burning more calories overall. But in the end, the time that you sleep can actually change some internal chemistry, which can make your body more likely to burn fat.
Calories and Sleep
Earlier in 2018, a study published in ”The Journal Sleep’‘ split subjects into two groups. For two months, one group cut calories and slept the regular amount while the other group cut the same amount of calories, but were put on a restricted sleep schedule.
They shortened their sleep by about one hour for five days a week and got to sleep however long they wanted to for two nights a week. Both groups ended up losing about the same amount of weight, but the group that didn’t mess with their sleep schedule actually lost a greater proportion of fat mass. That group also reduced something called their resting respiratory quotient, a number that tells you how much of your fuel is coming from carbs versus fat.
The group that slept just one hour more had a lower resting RQ, meaning at rest, they burned more fat. Keep in mind, this is just one hour’s worth of difference. Even worse though the group that slept for an hour less also had lower levels of the hormone, leptin, a chemical that signals to your brain, that the body is going into starvation mode the lower that that hormone gets.
It forces your brain to start looking for ways to save energy, including using less energy, but also increasing hunger, which is going to make you want to go for those calorie dense foods.
Leptin and Sleep
Lower amounts of leptin literally make it easier for your body to hang on to fat. And plenty of other hormones are tweaked when you don’t sleep, including the hormone insulin, that chemical that lets glucose into your cells, subjects and experiments that shorten sleep usually have impaired insulin sensitivity. Their muscles will actually use 20 to 30% less glucose than if they slept normally and now you’ve got a bunch of extra glucose hanging out in your blood.
Then there’s the so-called stress hormone cortisol, which is elevated the day after you decide to pull an all nighter extra cortisol works with insulin to tell your body, to store that extra glucose as fat. And remember, you’ve got lots of extra glucose now because your insulin is all out of whack.
Relationship between Food and Sleep
Now, every study that looks at sleep and weight loss is going to be a little bit different. So a meta analysis back in 2015, tried to gather as many good studies as they could and find some themes from it, but they didn’t see a super strong relationship between any of these metabolic measures. There was some extra weight loss among the subjects that slept more, but the results overall really weren’t that powerful.
But one thing that was consistent among all these studies was an increase in food intake, whether it was measured in calories or in portion size, being sleep deprived, made subjects more likely to eat. And those behavior choices totally make sense to me.
I know that when I was in grad school and only sleeping four hours a night, I would just grab whatever food I could. I don’t care if it tasted terrible. I just want it easy and convenient. As it turns out, it’s not just because you magically lose willpower and those croissants start looking at you with a comm heather, look, our brain chemistry actually changes a little bit to make all that food more appealing.
Relationship Between Ghrelin and Sleep
Other than leptin, turning your body into low power mode, it also signals for fullness. Remember, this is the one that is reduced when you don’t and leptin has to play this balancing game with another hormone called ghrelin, which raises your overall appetite.
More ghrelin typically means more hunger, but hopefully these hormones are imbalanced. And sure enough, a sleep study out of Wisconsin showed that people who slept for only five hours a night had a 15% elevation in ghrelin compared to subjects who slept their full eight hours.
Overall less studies look at ghrelin than those that look at leptin, but they all show that sleep deprivation either increases or doesn’t change the amount of ghrelin. None have showed that sleeping less makes you produce less ghrelin.
Sleep deprivation and Serotonin
Sleep deprivation also causes a decrease in serotonin that neuro-transmitter that signals for happiness among other things. You know, that sweet or salty foods will definitely bump up your serotonin at least when you haven’t been eating them for the last nine days.
But what if that sleep deprivation is being supplemented with exercise? Like what if I take that extra hour that I’m not sleeping and go work out instead? Science says that’s not going to happen for you. Not only are you more likely to skip going to the gym when you’re sleep deprived, but everything from peak power output motivation during exercise and the ability to recover are all dampened after sleep deprivation, even after just missing work on night of sleep.
So the end message is this while, and your coworkers are going to show up to work next week with their Tupperwares full of chicken and broccoli bragging about the new rock climbing gym they just joined, if you’re the one who commits to another hour of sleep tonight, you might be the one actually seeing results.