It's late. I've got a lot on my plate. A lot to do. And most of us do. So here I am, burning the midnight oil along with many of my neighbors. I usually count myself lucky to get 7 hours a night, and I AM lucky. For many parents or other caregivers, for example, 7 hours is unheard-of luxury.
But I am tired. And I'm snacking. Because, well. I'm up late and...and it's LATE. And if I don't eat, well I'll probably just fall over right now.
I'd like to think that my staying up late and my late night snacking are a once in a while thing...but really, it's almost every day.
Is it just me? Probably not. Most of us don't get enough sleep, and those who don't sleep? Snack. But why? And what does this mean for issues like obesity?
Markwald et al. "Impact of insufﬁcient sleep on total daily energy expenditure, food intake, and weight gain" PNAS, 2013.
We know that there has been an increase in obesity in this country. And many people are asking why. There are probably lots of reasons involved: too much sugar, too little exercise, genetics, too much fat. But what about sleep? It turns out that getting less sleep is a risk factor for obesity, but...how are sleep and weight gain related?
It turns out that sleep, or lack thereof, can have a lot of influence on how much we need to eat and how much we feel like eating. For example, sleep deprivation changes hunger hormone levels, which can change food intake, and some scientists hypothesize that decreased sleep can change energy expenditure as well.
But in order to understand just how lack of sleep influences weight gain, well you need to sleep deprive some people. The authors took 8 men and 8 women who reported getting an average of 8 hours of sleep per night into an inpatient facility. They were taken off caffeine one week before the study and were told to stick to 9 hours of sleep opportunity (stay in bed 9 hours) per night for the first week. They also were put on a diet that was calibrated exactly to maintain their current weight.
When they entered the study, they spent the first three days getting a baseline 9 hours of sleep. Then, for 5 days straight (in order to simulate a typical work week), they were limited to 5 hours of sleep per night. During that time they were allowed to eat both scheduled and unscheduled meals. Afterward, the patients were allowed to resume their baseline.
During the sleep periods, the authors measured their levels of ghrelin (which stimulates feelings of hunger), leptin (which subdues feelings of hunger), and melatonin, as well as monitoring their energy expenditure, what they ate, and how much. And of course, the participants were weighed.
What they found was that, while ghrelin was down and leptic was up during the 5 hours of sleep condition (which should mean you were LESS hungry, and in fact, the participants reported being less hungry), the participants all...gained weight. About 0.82kg, or 1.8 pounds over the course of 5 days, which is quite a bit! And they gained weight in SPITE of increase energy expenditure.
Here you can see the energy expenditure over 24 hours during the baseline sleep and long sleep conditions, and during the short sleep condition (the open squares). You can also see the two different 20 min stepping sessions they had participants go through to mimic outside activity. While the normal sleep condition resulted in decreased energy expenditure during darkness (as you might expect, they were sleeping), the 5 hour sleep condition energy expenditure remained high (because, of course, they were still awake). So during the low sleep condition, the participants were actually using MORE energy...but they were still gaining weight.
And why? They were substituting food for sleep.
What you can see here is the caloric intake at different time of day. The low sleep condition ate slightly less at breakfast, and didn't differ for lunch, dinner, or daytime snacks, but that nighttime snacking at the bottom right...that's very familiar.
The participants were taking in more food than they needed (in men, 70% more, and in women, 16% more). And the vast majority of it was carbohydrate.
Yikes. But the good news is that when they were put back on a normal sleep schedule, eating returned quickly to normal, and women actually lost a little weight. A little sleep goes a long way.
The authors hypothesize that when we sleep less, we eat more to make up for the increased energy expended by being awake longer. But in our current environment, where there's lots of food always available...well we'll take in even more than needed. And the results show that sleep may play an important role in how much energy we use and take in, and in the long run, might play a role in obesity.
But there are always caveats. First, this was a short term study, and these people were getting 8 hours of sleep per night previously. They were not USED to getting less sleep. It would be interesting to see if, long term, the body is capable of becoming "used" to less sleep and what that means for energy expenditure. And conversely, if we are used to sleeping less and taking in more food over a long period of time, can we still bounce back once we're getting enough sleep?
Secondly, the meals were all planned. While the subjects could eat as much or as little as they wanted, there's a lot of social pressure to clear your plate, and this may also have prevented them from eating WHAT they wanted. It would be interesting to see what the energy intake looked like if all their favorite or usual foods were present instead of just what the study gave them.
I'd also be interested to see how the low sleep might interact with something like stress, and how that might affect energy metabolism and food intake. After all, most of us aren't getting less sleep in a normal environment. We're doing it because we're stressed. What does that do to our hunger-related hormones? Or energy expenditure? Our food intake?
Future studies will hopefully look at these conditions. But in the meantime, I'm going to sleep. Before I start snacking again.
Markwald, R., Melanson, E., Smith, M., Higgins, J., Perreault, L., Eckel, R., & Wright, K. (2013). Impact of insufficient sleep on total daily energy expenditure, food intake, and weight gain Proceedings of the National Academy of Sciences, 110 (14), 5695-5700 DOI: 10.1073/pnas.1216951110