How does sleep affect body weight?

Experts have known for some time that there is a relation between being overweight and sleep. Evidence clearly points to sleep-related pathologies being more common amongst the obese, as being overweight makes it difficult to get adequate rest. The following meta-analyses of observational studies detail this relation:
Furthermore, in terms of the reverse cause-effect relationship, i.e. the impact of a lack of sleep on body weight, certain study findings also back up the hypothesis that disturbed sleep may exacerbate overweight. This is of particular interest as it may shed significant light on the issue of obesity prevention, but well-designed intervention trials would be required to confirm this perspective. And though, as mentioned above, some study findings do point to this being the case, there are many more that don’t.

For example, a 2010 study under the title "Insufficient sleep undermines dietary efforts to reduce adiposity" revealed that when a small group of individuals followed a weight loss diet and the amount of sleep they were allowed was restricted to around 5 hours per day, their percentage of fat weight loss diminished whilst, conversely, their loss of lean body mass (muscle and fibre) increased, which is not at all recommendable. In the 2003 study "Dietary Intake Following Experimentally Restricted Sleep in Adolescents", the authors restricted the number of hours sleep of the research subjects and found that, in those conditions, the subjects ate more higher glycaemic index foods and more sweets.

A body of similar studies was gradually built up and eventually led to a group of researchers undertaking a meta-analysis in 2015 under the title "A Systemic Review and Meta-Analysis of Randomized Controlled Trials of the Impact of Sleep Duration on Adiposity and Components of Energy Balance" (2015). These experts selected the randomised trials conducted to date on the effect of sleep restriction and the changes in body weight and drew the following conclusions:

"(...) This meta-analysis highlights some initial experimental data suggesting that the manipulation of sleep duration or quality may have significant effects on body composition and other energy balance related factors. The findings of this analysis call for additional research using more standardised methods and measures, as well as evaluations of associated outcomes with sufficient sample sizes and durations to ascertain whether a causal relationship truly exists between sleep duration and body weight regulation. Only then can we attempt to quantify the strength of any relationship".

The following figures show some of the results obtained:

Comparison of sleep improvement intervention studies and the effect of body weight compared to control:

Comparison of studies of sleep restriction and the effect on body weight compared to control:

Comparison of studies of sleep restriction on metabolic chamber measures of total energy expenditure or respiratory quotient:

A second meta-analysis was later published under the title "The effects of partial sleep deprivation on energy balance: a systematic review and meta-analysis" (2016). In this case, researchers compiled studies analysing the impact of sleep restriction on energy intake (EI) and expenditure (EE). The following figures show the results on EI, the variable where differences were found:

The authors concluded:

"Evidence [...] suggests that PSD may result in an increased EI, leading to a net positive energy balance of 385 kcal per day. In the long term, this may implicate weight gain: however, it remains to be investigated. We found no significant change in EE, although this may be attributed to variations in measurement techniques across studies. [...] Our results propose that sleep may be a potential novel target for weight management in addition to physical activity and dietary management".

Other recent reviews have produced similar outcomes, both in adults and children, with significant evidence pointing to the same conclusion whilst also acknowledging that more research needs to be done on this issue:

Fortunately, the subject seems to have captured the interests of scientists, with new studies and advances appearing from time to time. A case in point are the recently published results of a study which analysed the effect of shortened sleep on different weight-related variables: energy expenditure, body temperature and appetite. Under the title "Effect of shortened sleep on energy expenditure, core body temperature, and appetite: a human randomised crossover trial" (2017), experts subjected a small group of nine people to two sleep cycles of different lengths: one of 7 hours per day, the other of 3.5 hours per day. In line with the nature of crossover trials, all nine people were subjected to both cycles.

The authors concluded:

"[...] sleep restriction reduced gut hormones (PYY and GLP-1) and increased appetite sensations, but did not alter EE or substrate utilisation [...]. Moreover, a 3-night shortened sleep reduced CBT for 48 hours in healthy young men. Three nights of short sleep duration might lead to a positive energy imbalance. These findings suggest that the quality of sleep time leads to changes in individual energy balance and circadian rhythms and may increase the risk of obesity".

Considerable research still needs to be done on the reasons behind the negative impact of sleep restriction on the body’s metabolism, but most hypotheses revolve around an alteration of the concentration of certain hormones and of the functioning of the body’s reward circuit. Such changes may provoke an increase in appetite and a craving for tastier and more palatable foods which are generally of a more energy dense nature and eaten more compulsively.

The findings of the following studies point to this conclusion:

In short, on the basis of all this research, it’s fair to conclude that good sleep hygiene is likely to be a relatively important factor in the prevention of overweight. Perhaps this factor alone is not enough to lose weight, but it would seem that insufficient sleep may have an important impact on bad eating habits and, consequently, on increasing the risk of obesity.

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