Yes, it turns out how well you sleep may be affecting your waistline.
A new analysis of existing research found that not getting enough shuteye makes us eat more the following day ― nearly 400 calories more. And we tend to choose less healthy foods, too.
Over the long run those calories add up, according to Gerda Pot, the study’s author and a lecturer in the Diabetes & Nutritional Sciences Division at King’s College London.
“If long-term sleep deprivation continues to result in an increased calorie intake of this magnitude, it may contribute to weight gain,” Pot said. “And ultimately to obesity and [being] overweight.”
The new analysis pooled data from 172 people in 11 different studies that investigated how short sleep affected calorie intake. On average, the analysis found, people ate an additional 385 calories on the days after they hadn’t gotten a full night’s sleep ― ranging from 3.5 to 5.5 hours ― compared to days when they slept at least seven hours.
What’s more, when sleep deprived, people tended to eat more fat and less protein. That’s problematic because fat contains more calories per gram than protein and protein keeps you fuller longer ― so eating poorer quality calories therefore could be leading people to eat a higher quantity of calories overall, Pot said.
There are likely several reasons we tend to eat more when we don’t get enough sleep. One simple idea? “We simply have more hours to eat ― so more time to eat,” Pot said.
There is also evidence that short nights of sleep cause the body to produce more ghrelin (the hormone that tells us we’re hungry) and less leptin (the hormone that helps regulate energy and food intake and tells you when you’re full). And not sleeping enough throws off our circadian rhythm ― our body’s internal clock ― which also helps regulate when we’re hungry and when we eat.
The researchers acknowledge that the 400 extra calories our overtired selves eat per day (according to this study) may even be an underestimate because they only looked at lab-controlled experiments. So this data may not account for other real-life factors that affect how much we eat after a poor night’s sleep (we’re looking at you impulse, mid-afternoon pick-me-up brownie).
But the lab studies do allow the researchers to make a straightforward (and accurately measured) comparison of sleep time, calories consumed and calories expended.
And beyond this lab research, other studies have shown that being sleep deprived may make us more inclined to choose bigger portions and choose foods higher in calories and carbohydrates, too ― and make less healthy choices at the grocery store.
The bottom line: there’s likely several reasons we’re more likely to eat more when we’re overtired ― so it doesn’t hurt to pay extra attention to food choices if you know you’re not well rested. And feel good about catching all the Zs you need ― they could be helping prevent weight gain and obesity (and all the complications that come with both).
Sarah DiGiulio is The Huffington Post’s sleep reporter. You can contact her at sarah.digiulio@.