Eat fewer calories and exercise more – that’s the age old recipe for weight-loss. But research suggests that we should add one more element to the regime: Get a good night’s sleep.

Studies have shown a link between obesity and lack of sleep, but the association by itself doesn’t give much of a clue as to which came first and doesn’t prove causality. Obesity can cause sleep problems (the most serious of which is obstructive sleep apnea). Being awake at night can increase appetite and night-time-snacking (kale isn't a popular midnight snack), and sleep deprivation can lead to poor food choices and inactivity.

A new review article in The Journal of Health Psychology examines how sleep impacts food intake, and shows that when sleep is disrupted our hormones (such as leptin and ghrelin) drive hunger, our cognition is impaired -- leading to less impulse control -- and we tend to look for pleasurable stimuli such as food to reward ourselves out of our crankiness. 

A study in the Annals of Internal Medicine isolated the effect of sleep quite nicely; it looked at overweight adults on a weight-loss diet, and showed that all other things being equal, lack of sleep hindered the dieter's ability to shed excess body fat.

That study recruited ten overweight healthy adults who were fed a moderate calorie-restricted diet. Dieters were randomly assigned to sleep either 5.5 hours or 8.5 hours each night, for two weeks on each regimen, in a closed clinical research environment. The researchers measured weight, but also measured body fat directly (using dual-energy x-ray absorptiometry or DXA), so they could calculate how much of the weight-loss was loss of fat, and how much of it was lean tissue or muscle loss. The results in this small group were quite clear Although overall weight loss was similar whether the dieters slept 5.5 hours or 8.5 hours, sleep restriction resulted in more loss of muscle and less loss of fat. More than half the weight lost during the 8.5 hours sleep condition was fat, compared to just one quarter in the 5.5 hour sleep condition. During the two weeks of sleep restriction, the dieters also felt hungrier

Sleep and muscle mass during weight-loss

When we ingest fewer calories than we expend – which is what happens on a weight-loss diet – the body goes looking for energy stores, and will break down both fat and protein to make sugars for energy.

The goal of any diet is to lose fat, not muscle. Not only do we like our muscles' look and strength, muscles are active metabolically and burn energy, and loss of muscle during weight-loss diets is part of the reason people who've lost weight are so prone to regain it, and actually need to consume fewer calories just to keep their new weight stable. Preserving muscle is one of the reasons there’s such an emphasis on exercise during a weight-loss diet – working those muscles and building them is protection from dwindling muscle mass and slow metabolism. (For the sake of preserving muscle-bulk it’s also a good idea to avoid extremely low-calorie and nutritionally unbalanced weight-loss regimens.)

So a regime that protects muscle and leads to more fat-loss is very valuable. But don’t get excited just yet: This study involved only ten healthy participants, studied for a short while. But if results are confirmed by other studies this finding could be very important.

How could sleep affect fat loss? The researchers measured the levels of the hormone ghrelin and found that when dieters where on the sleep deprivation regimen ghrelin levels rose. Ghrelin, they reason, has been shown to signal hunger, reduce energy expenditure, hinder the breakdown of fat and increase the liver’s production of sugar. In this calorie deprived state of high ghrelin, the liver needs to make sugar while fat stores aren’t really open for providing building blocks, so it will break down muscle to fill the demand. There are, of course, many other possible ways in which lack of sleep may hamper fat-loss: fatigue may cause a dieter to be less active, and move less, for example.

More sleep less weight?

Sleep is one of the central pillars of good health. Sleep is absolutely critical to keeping us sane and happy. Yet we don’t give sleep as much respect as it deserves. 

Perhaps it's time to address sleep issues as part of any dietary intervention.

Dr. Ayala