Sleep 'affects weight loss'

“Good sleep is dream recipe to lose weight,” reported the Daily Express. People who get around eight hours sleep a night and reduce their stress levels have double the chance of slimming down, it continued.

This study looked for associations between sleep, stress and success at sticking to a weight loss programme. People who had less than six hours sleep or more than eight hours per day were less likely to achieve weight loss than those who had between six and eight hours. High stress levels also affected weight loss. When combined with poor sleep, stressed people were about half as likely to be successful at weight loss than their less stressed counterparts who got between six and eight hours of sleep.

The results support previous research linking sleep problems to obesity. The findings also make intuitive sense: people who aren’t getting enough sleep and are under stress may have more difficulty sticking to the demands of a weight loss programme. However, this association does not mean that poor sleep causes obesity, or that healthy sleep patterns are a means of achieving weight loss. It is possible that underlying health problems are associated with both poor sleep and obesity.

Where did the story come from?

The study was carried out by researchers from Kaiser Permanente Center for Health Research in Portland, US. Kaiser Permanente is a private health care company. The research was funded by a grant from the National Center for Complementary and Alternative Medicine, National Institutes of Health. The study was published in the peer-reviewed International Journal of Obesity.

The details of the study were generally reported accurately. The Express was incorrect in stating that people getting over eight hours sleep were more likely to lose weight.

What kind of research was this?

This research is a two-phase clinical trial aimed at comparing two different approaches to maintaining weight loss that has been achieved through a weight loss programme. This research paper concentrates on the first initial weight loss phase, constituting a non-randomised, intensive, six-month behavioural weight loss programme.

The researchers measured various factors to see how much they contributed to the success of the programme, including sleep time, screen time (e.g. TV watching), depression and stress levels. Phase 2, the randomised weight loss maintenance part of the study which will be comparing the two different approaches, will be reported at some point in the future.

They point out that disordered sleep patterns have been identified as a likely risk factor for obesity and that a growing number of experimental studies have observed that lower sleep duration is associated with weight gain. This may be due to sleep affecting hormone levels, which in turn are associated with feelings of fullness or hunger. Similarly, they say, an association has been found between screen time and obesity, and between depression and stress and obesity.

What did the research involve?

In this phase of the trial, researchers recruited 472 obese adults to a six-month intensive weight loss intervention programme. The adults had to be 30 years or over with a BMI of 30-50, and weighing less than 400lbs (28.5 stones or 180kg).

The programme was aimed at changing the participants’ behaviour. It involved:

  • reducing their dietary intake by 500 calories a day, with the aim of losing 0.5 to 2lbs weekly
  • eating a healthy low-fat diet
  • exercising moderately most days (at least 180 minutes weekly)
  • recording daily consumption of food, drink and exercise
  • setting short-term goals and action plans to achieve them
  • to attend all group sessions. There were 22 group sessions, led by nutrition and behavioural counsellors over six months

At the start of the trial, trained staff measured the participants’ weight and repeated this at each weight loss session that they attended, as well as at the final visit at the end of the six-month period. Participants who lost at least 4.5kg during this phase were eligible for phase 2 of the trial.

The researchers also recorded other measures at the beginning of the trial, including sleep time, stress levels, depression and screen time. The first three of these were recorded using standardised questionnaires.

They used the Perceived Stress Scale (PSS) to measure stress. This is a self-completed 10 item questionnaire with scores ranging from 0 to 40. Higher scores indicate greater stress in the previous month.

Statistical methods were then used to evaluate whether these factors had any association with success in the weight loss programme, as measured by eligibility for the second phase. They also looked for any association between weight loss and adherence to certain other measures, such as attending sessions, time spent on exercise and keeping food diaries.

What were the basic results?

Over the six-month period:

  • Average weight loss was 6.3 kg, with 60% of participants losing at least 4.5kg (10lbs) (and therefore were eligible for Phase 2 of the study).
  • Participants attended an average of 73.1% of sessions, completed 5.1 daily food records weekly and reported 195.1 minutes of exercise per week.
  • Measurements of both sleep time and lower stress (P=0.024) taken at the start of the trial predicted success in the weight loss programme.
  • In particular, people who reported sleeping between six and seven or between seven and eight hours daily at the start of the study were more likely to lose at least 4.5kg than those who slept six hours or less or eight hours or more.

People reporting both less than six hours sleep and the highest stress scores were only about half as likely to succeed in the programme and progress to the second stage, as those sleeping between six and eight hours, with lower stress scores

Changes in stress and depression levels during the study were also associated with changes in weight loss, although changes in sleep and screen time did not show any association with weight loss. Measures of attendance, exercise minutes and food diaries were all positively associated with weight loss.

Screen time did not have any association with success in the weight loss programme.

How did the researchers interpret the results?

The researchers say that early evaluation of sleep and stress levels in weight loss studies could identify which participants might need additional counselling.

They say that “chronic stress may trigger hormonal reactions that result in an intake of energy-dense foods, so that eating becomes a “coping behaviour” and palatable food becomes “addictive”. Lack of sleep may also affect hormones associated with feelings of fullness or hunger.


This study found that people who slept between six and eight hours a night had a greater chance of achieving their weight-loss goal than those who slept less or more. It also found that lower stress levels were associated with greater success at weight loss, particularly when combined with between six and eight hours of sleep. These findings support previous research linking obesity with poor sleep. It seems intuitive that if someone is not sleeping well and is under stress, then sticking to a weight loss programme will be more difficult.

It should be noted that the study relied on people self-reporting the hours they slept and their stress levels. This introduces the possibility of error. Although people with certain health conditions were excluded, it is possible that those who slept less (or more) had other health problems that also made it difficult for them to lose weight. Also, it is possible that people who slept longer were less likely to lose weight because they were less active generally, rather than because they were sleeping longer.

It is important to point out that the study does not imply that weight loss can be achieved by getting a healthy amount of sleep alone. Asking people about their sleep habits and stress may be a way of identifying those who could need more help with losing weight.

Sensible diet and exercise regimes are proven methods of achieving weight loss. It seems sensible that they would be more difficult to adhere to if people are not getting adequate sleep and/or are under stress.

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