In my experience as a trainer I have come to realize that losing weight and getting in shape is very challenging for the everyday person. Especially in America where work comes first and sleep second. We are encouraged to burn the midnight oil and told that that sleep is for the weak. Unfortunately, this couldn’t further from the truth. Lack of sleep is making people weak and fat. .The latest statistics from stateofobesity.org state that 38% of adults are obese and of that percentage, 8% are extremely obese. To put this perspective, 1 in 3 adults are obese. Yes, exercise and diet play a huge role, but they aren’t the only things that matter. After all, sleep determines what we eat and how we perform in the gym. However, we have forgotten how influential sleep can be. But don’t worry, by the end of this post you will know the importance of sleep and how it influences your hunger.

The National Sleep Foundation  recommends 7-9 hours of sleep per night, but according to their data, the majority of people are barely sleeping the recommended amount. According to the National Sleep Foundation the average person sleeps 7.5 hours per night from 11pm- 6:30am.  This lack of sleep wreaks havoc on the body causing a spike in hunger. I come across this frequently with my clients. They tend to make poor dietary choices and consume more meals on the days where they sleep less. This sparked my curiosity and led me to a study titled: Effects of Experimental Sleep Restriction on Weight Gain, Caloric Intake, and Meal Timing in Healthy Adults.

The study was published in the journal Sleep. It included 225 healthy adults, with 198 of them participating in the sleep restriction group and 27 of them in the control group (normal sleep). The sleep restricted group slept for 10-12 hours the first two nights and then slept a total of four hours per night for the next five nights. While the control group slept for 10 hours each night. In addition to the sleep restriction, the subjects in both groups were not allowed to exercise, but they did have access to books,television, and video games. Also, the subjects were encouraged to eat as little or as much as they wanted throughout the day.

By the end of the study, the sleep restricted group had gained significantly more weight compared to the control group (1). This is evident in the graph below:


As you can see from the graph, the sleep restricted subjects had a 1kg (2.2 lbs) weight change versus the control group. Now, this may not sound significant, but this weight gain occurred in only five days. Can you imagine how much weight the subjects would have gained if the study was extended for a month, or a year?

So why does sleep restriction cause weight gain?

The authors of this study believe that the delayed bedtime (sleep restriction) led to a higher calorie intake through increased meal frequency, but not through increased portion size.The scientists aren’t sure exactly why the meal frequency increased, but they hypothesized that it could be due to the hunger hormone, ghrelin, which is responsible for keeping us satiated. Generally speaking, when we are restricted from sleep (less than 7 hours) our ghrelin levels increase causing a spike in hunger (2). This spike in ghrelin could be the reason for the increased  meal frequency and ultimately the increase in weight gain. But I don’t think this was the only reason. In previous posts I have written about the benefits of time restricted eating and how late night eating can cause weight gain. I believe the increased meal frequency caused the subjects to consume more calories before bed which played a role in their weight gain and the authors agreed:

“Subjects consumed additional calories during the late-night period when they remained awake...We also observed an increase in the proportion of calories from fat during late-night hours; this increase may be particularly contributory to weight gain”(1)

However, this is only one study and it wasn’t without limitations. For example, I am curious to see what would have happened if the participants were allowed to exercise. After all, we do eat out of boredom and I wonder if this led to more calories consumed. Then again, both groups were restricted from exercise and only the sleep restricted group gained weight.

The human body is extremely complex. There are many questions that we don’t know the answers too, but we know for certain that sleep is needed in order for the body to function properly. We may not be entirely sure why inadequate sleep causes weight gain, but the data is clear. In one of the largest sleep studies done to date, the authors concluded that sleep restriction has been shown to promote weight gain(1). This study proves that sleep has an impact on body composition and must be included in the obesity prevention conversation. So if you are struggling to adhere to a healthy lifestyle, it is imperative that you fall asleep before 10:30pm. Trust me, it works.

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