Adequate sleep found to be important for healthy body composition

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Many individuals contend that weight control is all about diet and exercise. Of these, the research suggests that dietary change is likely to bring the lion’s share of benefits. However, body weight and fatness are not determined only by these lifestyle factors. Hormonal issues can play a part too. For example, if the thyroid gland is under-functioning, weight tends to go up. And my experience in practice is that if this issue remains untreated, practically no amount of eating less, eating well or increased exercise will put much of a dent in someone’s weight.

One lifestyle factor which may influence hormone levels and also weight is sleep. In fact, there is already a body of evidence which suggests that sleep restriction can alter hormones that control food intake. In particular, sleep restriction has been shown to boost levels of hormones that stimulate appetite (e.g. ghrelin) and suppress levels of hormones that that temper appetite (e.g. leptin). The end result can be increased food intake. See here and here for posts about research which suggests that sleep restriction can indeed cause individuals to eat more.

I was interested to read about a study in which the effects of curtailed sleep on body weight and composition was assessed. A group of adults were put on a calorie-restricted diet (10 per cent less than the amount calculated to maintain their weight) [1]. For two weeks, each of the participants was given a total of up 8.5 hours sleep a night. On another occasion, the same individuals spent a two-week stint in which sleep was restricted to no more than 5.5 hours a night. Actual sleep time, as well as body weight and composition was assessed over the both of the two-week periods.

During the longer sleep phase, average duration of sleep was about 7 and a half hours. In the shorter sleep phase, it was about 5 and a quarter hours.

The weight loss for both phases was about the same (an average of 3 kg/6.6 lbs). But the really interesting thing was that while during the longer sleeping time about half this weight loss was in the form of fat (3.1 lbs), during the shorter sleep time fat loss was only half this loss (1.3 lbs) was fat. Shorter sleep duration reduced the proportion of weight lost in the form of fat by more than half (55 per cent). Fat-free losses were greater in this group, and much of this would come in the form of muscle.

In short, curtailed sleep duration led to smaller fat losses and greater attrition of muscle.

Why short sleep should have this effect is probably complex, and almost certainly involves hormonal changes. One hormone that might play an important role here is cortisol. This hormone is secreted in response to stress, and plays a very important part in the stress response. Higher levels of this hormone can be secreted when sleep is curtailed.

One of cortisol’s effects is to encourage ‘catabolism’, which essentially means the breakdown of body tissues. And one potential target here is muscle, particularly those in the limbs. Cortisol also, however, encourages deposition of fat, specifically in and around the abdomen and trunk. The changes seen with curtailed sleep are consistent with raised cortisol levels, though this study did not look at this specifically.

While we may not know how curtailed sleep alters weight loss, this study does strongly suggest that adequate sleep is important for healthy body composition. It’s another piece of evidence which shows how good sleep habits may enhance health and wellbeing.


1. Nedeltcheva AV, et al. Insufficient Sleep Undermines Dietary Efforts to Reduce Adiposity. Ann Intern Med. 2010;153(7):435-41

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