If you’ve read any of the posts I’ve made you’ve already heard my recommendation to get more sleep. In fact if you read any of the blogs that I read, you’ve read a few other sciency posts on why sleep is important. Stephen Guyenet outlines a study in this one that found that people who got more sleep lost more weight from fat when they lost weight.
There’s a lot of information about why you should sleep more. Many of us don’t get enough for a variety of reasons. I have a strong feeling that our reduced sleep time is as influential as any other single factor in the rise of obesity. The CDC calls it a public health epidemic!
That report says: “According to data from the National Health Interview Survey, nearly 30% of adults reported an average of ≤6 hours of sleep per day in 2005-2007. In 2009, only 31% of high school students reported getting at least 8 hours of sleep on an average school night.”
Ok, so it seems pretty clear that lots of people aren’t getting enough sleep. I think there’s a lot of emphasis on the effects on our movement and exercise when we are not getting enough sleep. I’d like to highlight some big picture studies that talk about some of the hormonal impacts that occur from even short term sleep reduction.
We all know that one of the goals of exercise is to improve insulin sensitivity. Well these two studies show that just 7 days of 4-5 hours of sleep resulted in signs associated with insulin resistance in healthy young men:
In one of the studies they tried to attenuate the effect with modafinil, an alertness medication, which had no effect. This shows that it’s not just “fatigue” causing the metabolic changes, it’s neurohumoral. The reduced sleep causes real modifications in the people’s biology.
The gurus try to tell us that it’s the carbs increasing our appetite. Lustig is selling a “sugar blocks leptin” theory also. That has some merit to it, but what if it was more simple then that? What if we are sleeping on average 2 hours less per night then 40 years ago and THAT is making us hungry. What if wide swaths of America are overweight as much because we stay up too late watching TV or doing facebook? Well I’ve been thinking that may be the case ever since I saw this doozy:
This is a great study. It was a group of normal weight but relatively sedentary individuals. They were brought into the hospital and all their food was measured, but they could eat ad-lib. They were split into two groups and spent 2 nights in the lab getting used to the environment and getting their food measured, etc. Sleeping how much they wanted the first nights the groups were matched for sleep. Then they took the experimental group and limited them to 2/3 their normal, which in the study was an average of 5.2 hours while the control group continued to sleep an average of about 7 hours. This lasted for 8 nights. They continued to measure both groups calorie intake during that time and also measured their activity through a physical activity monitoring system (PAMS).
The results are pretty surprising. Mostly surprising at how big the change is. No change in activity levels between groups. No change to levels of ghrelin or leptin (which was actually the hypothesis). Huge change to calorie intake. The sleep deprived group increased intake by over 600 calories and the control group decreased by about 100 calories per day during the experimental period. Let me repeat: an hour and a half decreased sleep resulted in a nearly 600 calorie increase in intake. This persisted even after two recovery nights (where the experimental group slept a lot more than their baseline) with the calorie intake still being increased by ~150 kcal. This resulted in a statistically significant increase in weight over the study period of 0.9 kg (~2 pounds).in less than two weeks.
There are some limitations to the study. The groups were small and the experimental group had a much lower baseline intake during the free living period. This could imply some baseline metabolic differences between the two groups, but even that doesn’t bother me. Even without a control group this would be an interesting result. The fact that the controls aren’t perfectly matched, but still had roughly static intake during the study period does help suggest the increase in intake is heavily influenced by the sleep deprivation.
By sleep deprivation of course I mean, “being forced to sleep like large portions of the American population.”
Go to bed.