The Science Behind Sleep and Weight Loss
Hundreds of millions of people will begin their short but intense journey to, in order of commonality: exercise more, loses weight, eat healthier, save money, stop smoking, or learn a new skill. If any of those are you then Godspeed, awesome. I wish you all the best. But I want to put this out there: the resolution that always gets overlooked, the thing that makes your weight loss or fitness goal way easier, is sleep. Now, the science behind sleep has been getting a lot more attention in the last few years because of all the benefits of consistent sleep, but in this video, we’re looking at how sleep can impact weight and fitness specifically. Which, kinda seems counterintuitive. You’d think that by being awake, your heart rate is higher, so you’re burning more calories overall. But in the end, the time you sleep changes some internal chemistry, making your body more likely to use more fat.
Earlier in 2018, a study published in the journal Sleep split subjects into 2 groups. For 2 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 5 days a week and got to sleep however long they wanted to for 2 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. They also reduced something called their resting respiratory quotient, a number that tells us how much of your fuel is coming from carbs versus fat. The group that slept just one hour more had lower resting RQ, meaning at rest they burned more fat. Keep this in mind, this is just one hour’s worth of difference. Even worse, the group that slept less had lower levels of the hormone leptin, a chemical that sends a signal to your brain that says you’re in starvation mode if it gets really low.
Your brain starts looking for ways to save energy, including /using/fewer calories, and signaling for hunger, making you look for calorie-dense foods. Lower leptin literally makes it easier to hang on to fat. And plenty of other hormones are tweaked when you don’t sleep, like insulin, the hormone that allows glucose into your cells. Subjects in experiments that shorten sleep usually show impaired insulin sensitivity – their muscles will actually use about 20-30%/less/ glucose than if they slept normally. Now you’ve got a bunch of glucose hanging out in your blood. There’s also the so-called stress hormone, cortisol, which is bumped up the day after an all-nighter. Extra cortisol works with insulin to tell your body to store that extra glucose as fat, which, remember, you have more of now because your insulin is out of whack. Now, every study that looks at sleep and weight loss is going to be different, so a meta-analysis back in 2015 tried to gather as many studies as they could and find some themes. But they didn’t see a super-strong relationship between many of those metabolic measures.
Yeah, there was /some/ extra weight loss with groups that slept more, but the results themselves weren’t that powerful. But one thing that was consistent among all these studies was the increase in /food intake/. Whether it was measured as calories or portion size, being sleep deprived made subjects more likely to eat. And those behavior choices totally make sense to me. I know when I was sleeping 4 hours a night back in grad school, I would just grab whatever food I could find.
Turns out, it’s not just because you magically lose willpower and croissants start looking at you with a “come hither” look. Our brain chemistry actually changes to make unhealthy food more appealing. Other than leptin turning your body into low power mode, it also signals for a feeling of fullness. Leptin plays this balance game with another hormone called Ghrelin which raises your overall appetite. More ghrelin, more hunger,
but hopefully these hormones are in balance. Sure enough, a sleep study out of Wisconsin showed that people who slept 5 hours per night had a 15% elevation in ghrelin compared to subjects who slept a full 8 hours. Overall, less studies look at ghrelin compared to studies that look at leptin, but they all show that sleep deprivation either increases or doesn’t change ghrelin. None have shown that sleeping less makes you /less hungry/. Sleep deprivation also causes serotonin to decrease, that neurotransmitter that signals for happiness among other things. And you know that sweet or salty food lights up that serotonin and make you happy….
at least when you haven’t been eating them for the past 9 days. Okay, but what if the sleep deprivation is being substituted with exercise? Like, what if I take that extra hour of being awake and workout? Yeah, science says that’s not gonna happen. Not only are you less likely to choose to workout when you’re sleep-deprived, but your peak power output, your motivation, and your ability to recover from exercise are all going to be lower. Even after only one night of sleep loss. And that’s if you even made it to the gym.
So the end message here is that while all your coworkers are gonna start showing up to work with Tupperware of grilled chicken and broccoli next week while bragging about the new rock climbing gym they joined, if you commit to another hour sleep per night, you might be the one who sees the results they’re looking for. If you liked this video, I’d love to hear from you in the comments section. I’m starting to write videos for next year and would love to hear what you want to learn about. Have fun, be good. I’ll see you next week.