Sleep has to be one of the most indispensable factors for us to manage as active individuals or competitive athletes. Not surprisingly, sleep will often go overlooked in the big picture, getting overshadowed by training hard, nutrition, and the newest supplements on the market. No one immediately looks to sleep as a big enough player in what we’re doing day to day to work towards certain goals, but it serves a much larger purpose than you think. Not only does it impact your energy levels and recovery, but it could very well be the reason that some wind up being less adherent to their diet than they’d like to be without even realizing it.
There are plenty of studies that suggest a link between sleep restriction and weight gain. Some even go as far to say that shorter amounts of sleep are a risk factor for a higher body mass index (BMI) and even claim it as a predictor of one’s weight gain over time. Weight gain and weight loss can be attributed to a plethora of interrelated factors including, but not limited to, one’s psychology, environment, health, and individual circumstances. Unfortunately for some, sleep restriction or irregular sleep schedules is something that can’t be completely avoided (think shift work), but the study to be discussed can still highlight some important considerations regarding sleep and how it can impact the way we approach our meals day to day.
The primary concern of this study was to determine how deliberate sleep restriction would impact an individual’s weight gain, meal timing, and overall caloric intake. A novel characteristic of this study is the fact that this was done in a controlled laboratory environment. There are pros and cons to this choice that can be discussed further, but this essentially allows Spaeth and colleagues to validate the feeding, sleep, and wake times of the subjects which is a pretty great addition.
225 healthy individuals participated in this study, although it is important to point out that only a small subset of this population was observed regarding their subsequent caloric intake, weight gain, and mealtimes (about 37 people total). Subjects had no preexisting issues with sleep, nor did they participate in shift work (irregular sleep and wake hours). In order to make this sleep restriction applicable to the average person, the subjects chosen were those who self-reported their typical duration of 6.5-8.5 hours per night.
The subjects were randomized into 2 groups: sleep restriction (SR) or a control condition. The duration of the study was split into five “protocols” or phases, and these protocols essentially outline the days that make up the duration of the study period. The sleep restricted subjects always started with two baseline nights of sleep which consisted of 10 to 12 hours per night. Following the two baseline nights of sleep, SR subjects arrived at the laboratory and were prescribed 4 hours of sleep per night starting at 4:00 AM and ending at 8:00 AM for five consecutive nights. This would mean SR subjects would experience a period of extended wakefulness coming up to their first night of sleep restriction, since bedtime would be 4:00 AM.
Following the 5 nights of sleep restriction, SR subjects would return to a 10:00 PM bedtime and a small subset of this group would be given 1-2 “recovery days” of sleep consisting of 12 hours of sleep. Excluding baseline and sleep restriction nights, the remainder of the study was spent outside of the laboratory. The control group underwent lab supervision as well, but regardless of the phase that the subjects were currently undergoing the control group always got 10 hours of sleep per night.
While in the lab, none of the subjects were allowed to leave or participate in any kind of exercise activity. Subjects were allowed games, television, books, and other sedentary activities to do during their stay. This can be one of the bigger limitations of the study in the fact that a lab setting does not exactly mimic one’s true level of energy expenditure outside of this type of environment.
Subjects were able to choose meals based on a variety of options provided on a menu, selecting additional foods and drinks available in the lab’s kitchen, and via personal requests to lab monitors and the study’s coordinator. Instructions were given to eat as much or as little as they preferred during their stay.
Subjects were given ample time for meals throughout the day. This included three, 30- to 45-minute blocks of specified mealtimes (1 additional time block was added on SR days). In addition to this, subjects were essentially allowed to eat and drink whenever they felt like it, as long as it didn’t interfere with the administration of neurobehavioral tests.
An interesting, but not surprising, result of this study was that sleep restricted subjects ended up gaining significantly more weight than the control group. SR individuals experienced a larger increase in BMI as well. With that said, we can assume caloric intake changed during SR nights, which it did. For all SR subjects, caloric intake changed significantly between their baseline and sleep restriction days. During days where bedtime was pushed to 4:00 AM, SR subjects consumed more calories. Not only that, but an interesting finding here is that those additional calories were consumed during the late-night period of time the subjects had to remain awake (between 10:00-4:00 AM).
Average meal size didn’t change during sleep-restricted nights, although an increase in total meals was observed (possibly to make up for the added time to their day waiting for bed). Macronutrient ratios did not change very much either and were consistent throughout all protocol days, though it is worth mentioning that fat intake significantly increased on the last SR day (with carbs and protein remaining similar). This would greatly impact one’s ability to overeat and make it easier to do so during late nights as fat is the most calorically dense macronutrient.
While a portion of this study is done in a more controlled or “unnatural” environment from what we are accustomed to normally, these results show us some important implications for sleep and its ability to impact our nutrition and daily intake. While meal sizes were not impacted by a lack of sleep, subjects seemed to compensate, in a way, for the added waketime by adding calories throughout that period. This subsequently leads to weight gain and BMI increases, both of which are not conducive to the majority of health and fitness inclined individuals.
These subjects were not shift workers, but we do still have some insight here on what individuals with spontaneous or irregular work schedules can focus on in order to optimize their nutrition, training, and lifestyle habits. More than anything the body loves consistency, so if you find that your sleep schedule is different day to day, a good start would be to ensure that you get the same amount of rest each night and do the same for your feeding window each day. This allows you to hold some control over these variables and keep them in check while going about your less-than-ideal schedule.
If you want some more thoughts on shift work and our best tips, we’ve got a Team LoCoFit round table episode all about it as well! You can check that out here.
Written By Gillian SanFilippo
Spaeth, A.M., Dinges, D.F., Goel, N. Effects of experimental sleep restriction on weight gain, caloric intake, and meal timing in healthy adults. SLEEP. 2013; 36(7): 981-990.