Sleep deprivation is linked to weight gain in adults at cardiometabolic risk

As a randomised clinical trial, this study provides a high level of evidence. Although it included fewer than 100 participants, it remains highly informative. Its randomised crossover design, strong adherence, and the use of complementary assessments (including actigraphy, MRI, and others) make it an outpatient study that closely reflects real-world conditions, more so than the classic laboratory experiments involving severe sleep restriction. It provides causal evidence that six weeks of mild but sustained sleep restriction (up to 1.5 hours less sleep per night) results in a modest yet clear increase in body weight (+0.45 kg), waist circumference, and sedentary time in adults at high cardiometabolic risk. The main limitations are the relatively short duration of the intervention (likely insufficient to detect clear changes in fat distribution versus lean mass), the small sample size for subgroup analyses by sex or menopausal status, and the fact that the study population already had an elevated cardiometabolic risk. Consequently, the findings cannot be directly extrapolated to healthy individuals without this underlying risk. It is plausible that the effect would be similar, or perhaps somewhat smaller, in metabolically healthy adults, but this remains uncertain. From a practical perspective, these findings support the inclusion of sleep as a modifiable factor in strategies aimed at preventing obesity and cardiometabolic disease. However, the observed effect is modest, and longer-term evidence is still needed. From a public health perspective, I find these results particularly concerning. People are sleeping less and less because of increasingly long working hours and today's sedentary lifestyles, both of which contribute to weight gain and make it more difficult to prevent and manage obesity and other chronic diseases.

I find this study, which consists of two clinical trials, particularly compelling. Although the number of participants is relatively small, it clearly demonstrates the biological impact that sleep quality and duration have on health. The study design is especially robust: sleep restriction was objectively measured using wrist-worn actigraphy, with participants reducing their sleep by around 90 minutes per night (in practice, the average reduction was 78 minutes, which could simply reflect those evenings when we go to bed later than usual). Even over this relatively short period, participants gained almost half a kilogram on average. The intervention lasted only six weeks, but if this effect were sustained over time, as the authors suggest, it could amount to around 4 kg of weight gain over the course of a year. We already know that insufficient sleep adversely affects metabolic health. In this trial, in addition to weight gain, participants also experienced a modest increase in waist circumference. The authors suggest that sleeping less leads to increased compensatory sedentary behaviour, as well as hormonal changes, including higher leptin levels associated with increased fat mass. We now understand that metabolic health is closely linked to sleep health. Metabolic health is influenced not only by what we eat and how physically active we are, but also by stress and sleep. This is particularly concerning given the amount of time people now spend using screens, which often reduces the amount of sleep they get. As this study showed, delaying bedtime appears to encourage a more sedentary lifestyle and is also associated with metabolic changes, including increased leptin levels, which may contribute to weight gain. Sleep should no longer be regarded as a passive component of wellbeing, but as an active biological intervention. It should therefore be considered a cornerstone of the clinical management of metabolic disease, overweight, obesity and diabetes. A simple way of summarising these findings is that sleeping less can also make us heavier. Sleep deprivation promotes weight gain through its effects on physical activity and subtle metabolic changes. When managing patients with metabolic disease, overweight or obesity, improving sleep quality should be regarded as an important biological target alongside diet and physical activity.

Is the study of good quality?

“The study is well conducted and addresses a genuinely interesting topic about which very little is currently known. The idea builds on previous research, although none of those studies explored the issue in such depth. It also includes a sufficient number of participants to support the findings, as the design is based on data from two clinical trials.”

Are there any limitations that should be taken into account?

“Yes. The authors acknowledge several limitations in the paper, but, in my view, the most important is that the results are not conclusive. They found only a trend towards weight gain when sleep was restricted by an hour and a half, but there is no clear evidence to support a definitive association.”

What are the implications of the findings, and how do they fit with the existing evidence?

“It cannot be concluded that there is a relationship between sleep restriction and weight gain.”

To what extent can these findings be extrapolated to people without metabolic risk?

“Based on the data presented in this publication, we cannot extrapolate the findings to people with metabolic risk—only speculate. However, given the positive trend towards weight gain observed, I believe it would be very worthwhile to conduct longer-term studies incorporating a broader range of cardiometabolic markers, as the study’s hypothesis is consistent with the pattern suggested by the data.”