Happy Physiology Friday!
If you’ve ever felt insatiable after a night of poor sleep, you’re probably not alone. Many are well aware that, for some reason, a lack of sleep seems to make one particularly hungry the next day — and perhaps hungrier for foods that might not be so nutritious.
Sleep deprivation-induced hyperphagia (“overeating”), if chronic, could lead to excess weight gain and poor cardiometabolic and cardiovascular health. If you combine this with the fact that being sleep deprived also reduces the motivation to exercise, it becomes apparent why a lack of sleep is associated with such poor health outcomes. Indeed, poor sleep quality and quantity (sleep duration) have been tied to an increased risk for cardiovascular disease, diabetes, and obesity, among other health maladies.
But correlation (association) does not imply causation. Sure, individuals who sleep less may demonstrate worse health compared to “normal” sleepers, but this could just be the result of other confounding factors. Perhaps people who sleep less also engage in other unhealthy behaviors that predispose them to ill health.
New evidence provides some indication of a causal link between sleep loss and obesity, suggesting that if you sleep less, you may eat more, and this may have dire consequences for weight and cardiometabolic health.
In a study published in the Journal of the American College of Cardiology (JACC), 12 participants completed a randomized, crossover investigation to compare the effects of sleep restriction and normal (control) sleep on energy intake, body weight, body fat and fat distribution, energy expenditure, and appetite hormones.
Each 21-day inpatient condition began with a 4-day acclimation period and ended with a 3-day recovery period — during which participants were given a 9-hour sleep opportunity. Between these, participants completed a 14-day sleep intervention consisting of either sleep restriction or control sleep.
In the sleep restriction condition, participants were limited to 4 hours in bed per night, whereas in the control sleep condition, they were allotted 9 hours in bed. Total sleep duration between the conditions ended up being different by around 3.5 hours.
Throughout the 21-day study, participants were allowed ad-libitum access to food. In short, they could eat whatever they wanted, whenever they wanted. This is one of the major strengths of the study, since this condition mimics real life where 24/7 access to food is an (unfortunate) reality for most.
Sleep restriction led to a 17% increase in calorie consumption, and participants ingested around ~300 calories more when they were sleep restricted compared to when they were well rested. This increase in energy intake came primarily from an increase in protein and fat consumption, which increased by ~13% and ~17%, respectively. This result may be surprising to those who claim that cravings for carbohydrate-laden foods are particularly apparent when one is sleep deprived.
As a consequence of the elevated energy intake, body weight and body fat both increased, which interestingly, occurred in both the control and sleep restriction groups. However, during sleep restriction, participants gained significantly more weight compared to during normal sleep — about 0.5 kg or ~1lb more to be exact.
Where participants gained fat was different between conditions.
During sleep restriction, participants gained fat primarily in the abdominal fat area, gained more subcutaneous fat compared to the control condition, and increased their visceral fat by 11%. In contrast, no changes in visceral fat were observed in the control condition.
No changes in energy expenditure — how many calories participants burned at rest or during normal daily physical activities — were observed in either condition. Similarly, there were no changes in appetite-regulating hormones including leptin and ghrelin, the stress hormone cortisol, or the endocannabinoids 2-AG and anandamide.
This study is one of the first to observe that sleep loss directly causes weight gain as a result of increased energy consumption.
In a previous newsletter, I wrote about a study that seems to compliment these findings in the reverse direction. Sleep extension (adding ~1.2 hours of sleep per night) was shown to decrease energy intake in individuals with obesity, which led to a significant reduction in weight.
It appears that both sleeping more and sleeping less have profound effects on appetite and weight regulation.
Even though weight increased in the normal sleep and sleep restricted groups in this study — likely the result of their having unlimited access to food — participants gained more when sleep restricted. Considering physical activity levels and energy expenditure were the same between conditions, it seems that sleep restriction uniquely affects physiology in some way that predisposes to excess weight gain.
Not only did sleep restriction lead to increased fat mass, but the type of fat mass gained — abdominal visceral fat — is the more harmful type of fat that contributes to insulin insensitivity, inflammation, and is associated with cardiometabolic disease. Even after the 3-day recovery period when weight had returned to normal, sleep-restricted participants displayed higher levels of visceral fat.
The mechanisms behind why sleep restriction led to increased food consumption and unique changes in fat deposition are unclear. None of the appetite or other regulatory hormones assessed seem to be responsible, so this is likely an area for future research.
I have tended to believe that the reasons for eating more during periods of reduced sleep are simply due to being awake for longer (and thus having more opportunities to eat) or the result of a slight increase in appetite secondary to increases in energy expenditure. Less sleep generally means you’ll be more “active” or at least using more energy to maintain wakefulness compared to if you were sleeping. This study doesn’t support that hypothesis — participants neither expended more energy nor were they more physically active during the sleep restriction condition.
How can you apply these findings? For one, if you are trying to reduce your energy consumption for weight management or to improve body composition, you need to be sleeping enough! 7–9 hours per night is probably ideal for most of us. Sure, a bit of self-control can go a long way, but without sufficient sleep, it seems as if our ability to self-regulate is somewhat impaired when it comes to food choices.
In addition, even in the absence of changes in weight, insufficient sleep could negatively impact how and where our body partitions and stores fat. Body composition and body fat distribution (i.e. where we store most of our fat) are crucial arbiters of disease risk. The stubborn “belly fat” that so many complain of is also the most lethal type — and could be the result of poor sleep habits. Perhaps the reason why it’s so hard to shed those last few pounds has something to do with the bedroom rather than the kitchen.
Maybe your experiences align with these findings. Does poor sleep lead you to eat more? Does better sleep help you regulate your diet? I’d love to hear about it in the comments.
Thanks for reading. See you next Friday.
Covassin N, Singh P, McCrady-Spitzer SK, et al. Effects of experimental sleep restriction on energy intake, energy expenditure, and visceral obesity. Journal of the American College of Cardiology. 2022;79(13):1254–1265.