We all know we should get more sleep, we're just not very good at it. In fact, we're so BAD at it that 28.3% of us (as of 2007, anyway) got less than 6 hours of sleep per night. Really, are we surprised? After all, there are kids that wake up in the night, stress that keeps us awake, always more things to do, multiple jobs, and only so many hours in the day.
But that lack of sleep can have some not so great effects on our bodies. It decreases things like cognitive performance, increases anxiety, and...it's not good for our waistlines. Sleep loss is associated with higher caloric intake, when you can't sleep you eat. But does this increased caloric intake translate to weight gain?
Spaeth et al. "Effects of Experimental Sleep Restriction on Weight Gain, Caloric Intake, and Meal Timing in Healthy Adults" Sleep, 2013.
The biggest positive point of this study on sleep restriction was how LARGE it was. When doing human studies that are not large scale surveys (which usually involve phone calls or mail in or online and therefore are less expensive) it costs a LOT of money to bring some people in to the lab to do nothing but hang out and sleep for a week, especially if you are watching for things like food intake (and controlling what they eat). I'm very pleased that they got these numbers, 225 people!
The authors took these 225 people, and brought them into the lab. They got two baseline nights (to see how much they naturally slept), 5 sleep restriction nights, and then another 2 recovery nights. But unfortunately, they did not balance the control and sleep restriction, where they were restricted down to FOUR HOURS a night of sleep (ick). They only had 27 controls out of all of these (people allowed to sleep fully all the nights of the study), the rest were sleep restriction. I have to wonder why they did it this way. While the two original nights and the two recovery nights could in theory serve as a partial control, I don't think that those would work. After all, if most people are slightly sleep restricted, the original two nights will be recovery as well, and both sets of recovery nights may not be representative of optimal sleep.
During the study, a very small subset (31 people) of the patients had their caloric intake measured. They could choose food options from a menu or small kitchen nearby, were not restricted in what they could eat, and all the food was recorded and weighed.
And what did they find?
Sleep restriction is not good for your waistline.
What you can see above is the average weight gain for men and women, Caucasian and African-American, following sleep restriction. EVERYONE gained weight after sleep restriction, but men gained more than women, and African American males gained the most. Now, remember "the most" is relative, average weight gain was around 1 kg (or 2.2 lbs), with African American men gaining an average of 1.4 kg or 3.1 lbs. So it's not really that much, but imagine if it were weeks and weeks and weeks of just a few pounds.
But of course, all this weight has to be coming from somewhere. Where is it coming FROM?
Here you can see the daily caloric intake of the 31 people they measured on sleep restriction. You can see that people generally consumed more calories than was good for them at baseline (2500), but this increased with sleep restriction up to 3000 calories per day! Lack of sleep snacking indeed.
And you wonder...on what were they snacking? Were they eating more in general or was there something specific? Well it turns out, when you sleepless-snack, you sleepless-snack on carbs.
(Click to embiggen)
It's small, but what you can see above are the days of sleep restriction (going down the left hand column, where SR is a day of sleep restriction) and the number of grams of each TYPE of food eaten (carbs, fat, or protein) in the columns on the right. While the fat and protein didn't really move, when people were eating sleep deprived, they were definitely eating more CARBS.
So sleep restriction, even for 5 days, produces measurable weight gain (in a very large sample), and for those people who had their calories tracked, that weight gain was coming from carb snacking.
The pros of this study: it was LARGE, 225 is a good number. And it was diverse, 63% were African American and 45% were female. This is one of the best of these studies for diversity and number. BUT, the control and sleep restriction numbers were very skewed, and sadly, while they had a very large and diverse sample with regard to weight in and weight out (I wonder if they needed these kind of numbers to get significance on the weight measures. After all, 3 lbs can be water weight for some people), they only had calorie intake data on a very SMALL sample. It's much more complicated to get, and so I understand why, but it would be, I think, a more complete paper if they had used the large sample to do something similar to the small sample study I featured a few months ago. The people on sleep restriction are gaining weight...where is that weight coming from? At what time of day is it being taken in, and what does it generally consist of?
In addition, I've seen a couple of sleep restriction studies now, looking at the relationship between sleep loss and weight gain. Sleep restriction changes eating-related hormone secretion as well as eating habits. But I'd also be interested to see a longer term series of studies. Most of these sleep restriction studies really can't do much more than a week of keeping someone in the lab. And the survey type studies which associate things like weight and sleep length can't account for other factors (what foods are available, socio-economic status, genetic history, etc). It'd be interested to get a really long term sleep deprivation study going, one for a month or so, and see if the weight gain continues, or if there's some point where your body just...gives up and gets used to it? Not only that, the subjects were NOT allowed to exercise at any point during the study. So for people who don't get enough sleep, is the caloric intake offset by exercise, if they can get exercise?
And of course, what these and other studies DON'T tell us is...how to get more sleep. I'm not just talking relaxation techniques, but rather, who takes care of your kids/parent/other dependent when THEY won't sleep or wake up in the night? How do people make enough money that they don't need to work that second job that whittles away at their sleep? How do we promote things like healthy eating habits and exercise that make it easier to nod off (and help with the eating extra bit), without, of course, impinging on that time needed to get adequate sleep? These are policy questions more than science. All that science can tell you is that when you're not sleeping, you're probably snacking, and that can't be good for any of us.
Spaeth et al. "Effects of Experimental Sleep Restriction on Weight Gain, Caloric Intake, and Meal Timing in Healthy Adults" Sleep, 2013. DOI.