Disrupted sleep can stop you burning fat

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I’m a huge advocate of sleep. There is a mass of evidence which bears testament to the importance of sleep’s role in physical and psychological wellbeing. The other thing is – it’s free.

In recent years there has been growing interest in the scientific community regarding the relationship sleep has with risk of obesity. Generally, the data here has shown a ‘U-shaped’ association, with enhanced risk of obesity seen in individuals who either sleep for very short or very long periods.

Lengthy sleep might be a marker for ill-health, and enhanced risk of excess weight from conditions such as Type 2 diabetes and low thyroid function. Also, there’s just a possibility that long sleepers have relatively sluggish metabolisms, and are generally tired and inactive. As a result, they risk being in ‘positive energy balance’ and gaining weight as a result.

What about those short sleepers though? Well, of course, these individuals may be tired and sluggish during the day (because they’re not getting enough sleep) and be less active over time as a result. However, there is also some evidence that hormonal changes may play a part here too. For example, curtailed sleep has been found to raised levels of the appetite stimulating hormone ghrelin and lower levels of the appetite suppressing hormone leptin. Curtailing sleep has been found to make some people hungrier and eat more. It’s also been found to induce insulin resistance, which is likely to predispose to weight gain.

I was interested to read a study this week in which the effects of ‘sleep fragmentation’ on a variety of metabolic processes was tested [1]. Basically, a group of young healthy men were tested in a ‘respiration chamber’ for two days while they got about 8 hours of sleep each night.

On another occasion, the men were woken by an audible alarm every hour and required to get up to turn the alarm off. This not only interrupted their sleep, but also meant they got less sleep (about 6.5 hours a night compared to about 8 hours a night when there was no alarm).

The results of this study showed that the amount of energy these men metabolised when sleep was disturbed was actually a little higher than before. This seemed to be down to increased activity, which the authors put down to having to get up repeatedly during the night.

Scores of exhaustion roughly doubled under the disturbed sleep conditions, and symptoms of sleepiness increased considerably too.

Perhaps the most interesting findings from this experiment related to the men’s metabolism, and specifically, the rate at which the men metabolised carbohydrate and fat.

In moving from uninterrupted to interrupted sleep, carbohydrate metabolism went up from an average 324 to 346 grams/day (statistically significant).

At the same time, fat metabolism dropped from 61 to 29 grams per day. In other words, the rate at which these men burned fat dropped by half over just two nights of interrupted sleep.

In general terms. I think it’s a gooccccd idea to be an efficient metaboliser of fat, and one nutritional trick that is believed to have merit here is a relatively low-carb, fat-rich diet. However, it seems from this study that if we want to burn fat optimally, it’s important to ensure we get a decent amount of uninterrupted sleep whenever possible.


1. Hursel R, et al. Effects of sleep fragmentation in healthy men on energy expenditure, substrate oxidation, physical activity, and exhaustion measured over 48 h in a respiratory chamber Am J Clin Nutr 2011 First published online July 27, 2011.

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