When it comes to losing weight, we all know the drill. Cut down on carbs, load up on veggies, avoid processed food, hit the gym, skip the cake. But did you know that sleep can, literally, tip the scale on weight loss?

Researchers have puzzled over the connection between sleep and weight maintenance for a decade. They’ve looked at links between sleep duration and obesity, the behavioral impacts sleep deprivation has on food choices, how sleep affects hormones that regulate weight, as well as how much (and what) we eat after a night of restricted sleep.

Although sleep is often overlooked in most weight loss programs, the growing body of research suggests it needs to be considered as part of any successful weight loss plan.

Hormonal changes are to blame

  • Many academic studies, like this study in 2004, show that sleep duration may be an important regulator of body weight because of the role of metabolic hormones in our bodies. Participants with shorter sleep had reduced levels of leptin and elevated levels of ghrelin, the two major players in the human body that regulate appetite and weight gain. Ghrelin is secreted inside the stomach and increases hunger. Leptin, on the other hand, is secreted primarily in fat cells and decreases hunger.

The study found that chronic sleep restriction and changes in these appetite regulating hormones may contribute to obesity. In Western cultures, where food is widely available and sleep often suffers from a highly stressful lifestyle, the problem is exacerbated.

Sleep less, eat more

  • Researchers at King’s College London, conducted a meta-analysis in 2016 of multiple studies and found that, “Sleep deprivation may result in people consuming more calories the following day.” Exactly how many calories is up for debate.
  • One randomized control study found that missing hours of sleep equates to eating 559 calories more the following day! In the study, 12 healthy men were allowed either eight or four hours of sleep. Their food consumption, physical activity, feelings of hunger and desire to eat certain foods were tracked. The sleep-restricted group ate an average of 559 more calories.
  • A similar study divided participants into a group that slept normally, and a group that got one third less sleep than normal for eight nights in a row. Both groups were allowed to eat whatever they wanted. Subjects in the shorter sleep group consumed 594 extra calories per day.
  • The International Journal of Obesity found that sleep problems likely contribute to weight gain. The study looked at BMI and sleep issues for men and women in a five-and seven-year follow-up. It concludes that “to prevent major weight gain and obesity, sleep problems need to be taken into account” and more research is needed.

It’s all in your head

  • This pivotal study from the brainiacs at University of California Berkeley went deep inside the human brain to find out how sleep deprivation affects brain activity when it comes to food desires and choices. Being deprived of one night of sleep, they found, decreased activity in the frontal cortex and insula cortex (the areas of the brain that evaluate appetite) and led to some serious amplification in the amygdala (the reward center of the brain). Translation: sleep deprivation causes our brains to seek the donut instead of the apple.

The science around sleep and weight regulation is evolving, but it’s clear that skimping on sleep is detrimental to our weight. Lack of sleep disrupts our appetite-regulatory hormones and actually wires our brains to seek out calorie-dense junk food. We’ve been trained to associate weight loss with will power, but the research suggests a deeper culprit: sleep.