Should You Try to Pay off Sleep Debt on Weekends?

We all occasionally have periods of time in which we don’t get as much sleep as we’d like. When we repeatedly restrict our sleep like this, we soon suffer from widespread deterioration in metabolic health, brain function, and more.

As I’ve discussed on the blog before, when people who have been habitually restricting their sleep then extend their sleep, they experience improved health and performance. These sleep extension studies generally involve prolonging sleep for at least a week, but a more common scenario is for people to try to pay off sleep debt on weekends after restricting their sleep before workdays.

Scientists have therefore attempted to study the effects of this pattern. The most recent of these experiments was done by Ken Wright from the University of Colorado Boulder, a scientist whose work I admire greatly. The study explored the effects of weekend recovery sleep on food intake and insulin sensitivity, a key determinant of risk of developing diabetes. The research received lots of attention and sparked much discussion, so in this blog we’ll explore it in more detail.

The experiment was impressively well carried out, and it must have been tough to do. It isn’t the easiest study to describe and make sense of, and this is perhaps why some of the more simplistic descriptions of it in the popular press are a bit misleading. I’ll do my best to not get bogged down in minutiae, but I’m keen to share details of the research that are important to interpreting it.

To begin, let’s review what the scientists did.

The participants were healthy but sedentary young adults (50% female). To document their baseline sleep patterns, they wore Fitbit-like devices for one week before visiting the lab. For the last three of these days, they were given baseline diets designed to maintain their bodyweights, and participants were prescribed brief exercise sessions to standardize their physical activity at this time too.

Participants were then divided into three groups, and all of these people then spent nine nights in the lab:

During the nine nights, the participants had access to as much food as they wished. They were kept indoors in typical room lighting (the rooms had windows), and they were sedentary other than two, 20-minute exercise sessions each day in which they repeatedly stepped on and off low steps.

On the final day before the experiment, participants were kept in very dim light to assess their melatonin rhythms. This was repeated on the first Tuesday and the second Monday. As I explain in the humanOS courses on our bodies’ clocks (available to Pro members), melatonin is primarily synthesized during the biological night and is the best marker of the timing of the clocks in our brains that orchestrate when our bodies are prepared for certain activities (physical activity, digesting food, and so on).

To record sleep during the experiment, the researchers used polysomnography on the first Monday and Tuesday, the Friday, the Saturday, the Sunday, and the second Monday. Polysomnography basically entails covering people in electrodes and wires to record brainwaves, blood oxygen concentration, heart rate, breathing, and eye and leg movements. It’s uncomfortable, but it’s the gold-standard way of measuring sleep.

To determine the effects of sleep patterns on how effectively the participants disposed of glucose in their blood, the scientists measured intravenous fasted insulin sensitivity at baseline (on the first Monday) and on the morning of the second Tuesday.

Now that I’ve spent so long describing what the scientists did, what did they find?

Sleep restriction led to more than 12 hours of lost sleep over the whole working week. Needless to say, weekend recovery sleep didn’t allow participants to fully repay this debt – from Friday night to Monday morning, they only slept a total of 1.1 hours more than they did at baseline. The analysis of the polysomnography data collected on the weekend also suggests that participants still had a sleep debt after weekend recovery sleep.

On the second Monday, the melatonin rhythms of participants in the sleep restriction group were delayed by about 25 minutes. However, after weekend recovery sleep, participants’ melatonin rhythms were delayed more still – by roughly 1.4 hours. This disparity between groups probably resulted from differences in their patterns of light exposure.

During sleep restriction, participants consumed substantially more calories than their baseline needs, and much of this extra energy came after dinner. As I have discussed before on the blog and elsewhere, consuming food late in the day tends to be more obesogenic than consuming it earlier.

Weekend recovery sleep reduced energy intake from post-dinner snacks during the weekend, as well as energy intake from pre-dinner snacks during and after the weekend. This suggests some positive effects of recovery sleep on dietary choices.

Nevertheless, by the end of the study, participants’ bodyweights increased similarly in the sleep restriction and weekend recovery groups (by 1.4 and 1.3 kg, respectively). So, the effect of recovery sleep on energy intake didn’t prevent weight gain.

In the control group, insulin sensitivity did not change during the study. In the sleep restriction group, however, whole-body insulin sensitivity declined 13% below baseline after eights nights. By this time in the weekend recovery group, whole-body insulin sensitivity was 27% worse than at baseline.

While the study wasn’t really designed to test this, the researchers explored whether men and women differed in their responses during the experiment. During weekend recovery sleep, women did not sleep longer than at baseline, despite spending more time in bed. What’s more, while men in the weekend recovery sleep group consumed substantially more energy during the first work week (72%), the weekend (40%), and the second work week (65%), these changes were smaller in women (30%, 2%, and 25%, respectively). Given these findings, it’s no surprise that bodyweight increased in men (by 3%) but not women.

In summary, weekend recovery sleep wasn’t enough to repay the workday sleep debt and led to similar weight gain to continuous sleep restriction. In some ways, weekend recovery sleep resulted in worse outcomes than sleep restriction – after all, weekend recovery sleep led to a larger delay in melatonin synthesis and greater deterioration in insulin sensitivity. Believe it or not, I’ve actually glossed over many details of the study in this blog – it had a lot of moving parts and nuances.

Anyway, based on the results, trying to catch up on sleep loss seems a bad idea, right?

I don’t think so. Here are some reasons why:

First, looking at all available studies (including 1, 2, and 3), whether weekend recovery sleep is beneficial or detrimental likely depends on what is being measured, and please note that the latest findings differ from those of similar previous research. For example, one experiment that used similar methods to Wright’s found that weekend recovery sleep reversed the negative effects of workday sleep loss on insulin sensitivity. These results are in line with those of an earlier study of men who habitually restricted their sleep during the working week.

Next, ask yourself this: How representative is the latest study of the kind of workday sleep loss you experience?

There are good data on how people in countries such as the US spend their time. A brilliant recent analysis of how Americans used their time between 2003 and 2016 showed that US citizens have been spending more time in bed at night in recent years.

This makes me happy!

What’s more, among US adults, time in bed on weekdays is typically over 8 hours per night. They do tend to spend longer in bed on weekends, but only a little, and they achieve this through later rise times. Yes, these are of course averages, and they don’t inform us how long these people sleep per se. However, the data do show that the kind of sleep restriction enforced in Wright’s study isn’t necessarily representative of how most of us generally transition between workdays and free days.

Sleep aside, consider also the study setting. The participants had access to as much food as they desired. While not statistically significant, even the control group gained 1 kg, on average. Physical activity was constrained too. To be clear, these variables were consistent between conditions, and the study was very tightly controlled. So, we can attribute differences in outcomes between groups to differences in their sleep. However, if these people were not in what was basically a nine-day long buffet and were permitted to move more, it’s possible that the differences between groups would have differed.

The advice I’ve been giving and will continue to give is to try to catch up on lost sleep when you can. Studies like this certainly make me less sure that this is always the best recommendation, but I do think it’s still smart to try to accumulate as much sleep as you can over time. I think about sleep in the same way that I think about the role energy intake in bodyweight regulation – occasional overeating is fine, the most important thing is calorie intake over longer periods (a week, for instance).

Now, when you sleep in after losing sleep, I suggest you do the following things to avoid your recovery sleep from delaying your body’s clock:

Sleep well tonight!

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