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Sleep not, gain a lot (of weight), suggests a new review published Wednesday in the European Journal of Clinical Nutrition.

UK scientists analyzed 11 earlier studies looking at the effects of sleep deprivation on calorie intake. Several of the studies involved comparing people who willingly got 3.5 to 5.5 hours of sleep a night to those who slept anywhere from 7 to 12 hours. Despite being awake longer, these fitful sleepers didn’t expend significantly more energy during the next 24 hours than regular sleepers did, and because they also ate more while awake, they ended up taking in more calories than their counterparts. On average, they took in 385 calories more per day.

“The main cause of obesity is an imbalance between calorie intake and expenditure and this study adds to accumulating evidence that sleep deprivation could contribute to this imbalance,” explained senior author Dr. Gerda Pot, a researcher in the Diabetes & Nutritional Sciences Division at King's College London, in a statement released by the university. “So there may be some truth in the saying 'early to bed, early to rise, makes a man healthy and wise.'”

Pot’s team also found that deprived sleepers adopted a slightly different diet, noshing less on proteins but more on fats, with the latter having more calories per gram. The amount of carbohydrates they ate, however, stayed the same.

There are likely numerous reasons why poor sleep can contribute to weight gain. Citing a small study of 26 volunteers, the researchers noted that people's brains behaved differently when sleep deprived, with the areas associated with reward lighting up more when presented with food than they did under normal circumstances. That might indicate that sleep-deprived people become more motivated to seek out food. Elsewhere, other research has shown that messing with our internal body clock can trigger a wealth of health complications over the long run, including obesity, by disturbing the production of hormones. And the lack of sleep may make us less able to exercise regularly. 

While the ‘how’ is certainly important to figure out, Pot and his colleagues hope to use these latest findings as a springboard to more proactive research. In particular, by using sleep as a weapon against obesity.

“Our results highlight sleep as a potential third factor, in addition to diet and exercise, to target weight gain more effectively,” said lead author and fellow King’s College researcher Dr. Haya Al Khatib. “We are currently conducting a randomised controlled trial in habitually short sleepers to explore the effects of sleep extension on indicators of weight gain.”

The researchers also hope to study the link between sleep and weight gain for longer lengths of time and outside of controlled situations in the lab.

Source: Al Khatib H, et al. The Effects Of Partial Sleep Deprivation On Energy Balance: A Systematic Review And Meta-analysis. European Journal of Clinical Nutrition. 2016.