Apparently, even just one night without sleep leads people to view junk food more favorably than when they’re well rested. 

Healthy eating is en vogue today, but that doesn’t necessarily mean the food that’s marketed as such is actually good for you. In fact, it can be tough to truly understand the hard line between health food and junk food at times if we want to honestly examine the nutritional content of what’s made available to us. One thing that’s not up for debate though is the prominence of junk food. It’s easy to get and sometimes it can seem as if fast food and processed foods are the only things you can find in a pinch. Of course, our bodies weren't made for processing this kind of food and so consuming it regularly can (and does) have adverse effects on our health. 

The findings of one new study suggest that there’s a direct link between a lack of sleep — something that can have profound negative health impacts — and eating junk food. So what was the discovery? Apparently, even just one night without sleep leads people to view junk food more favorably than when they’re well rested.

Disrupted sleep has already been found in other studies to impact hormone levels and even show a correlation to simply gaining unfavorable inches, and how hungry or full people feel seems to be one factor swinging throughout these studies. This most recent study published in the Journal of Neuroscience, however, says that this may all just be because a lack of sleep impacts brain activity involved in reward and regulation. 

“Whereas previous studies linked this weight gain to disturbed endocrine parameters after sleep deprivation (SD) or restriction, neuroimaging studies revealed up-regulated neural processing of food rewards after sleep loss in reward-processing areas such as the anterior cingulate cortex, ventral striatum, and insula,” the report reads.

“Our data brings us a little closer to understanding the mechanism behind how sleep deprivation changes food valuation,” said Prof Jan Peters, a co-author of the research from the University of Cologne. 

For this study, researchers observed 32 healthy men between 19 and 33 years old, giving them all the same dinner: pasta and veal, an apple, and strawberry yogurt. Afterward, each subject was either sent home with sleep-monitoring devices they would wear throughout the night or kept occupied in the laboratory overnight with activities like games. The next morning they would all return to the lab for surveys as well as measuring blood sugar levels and even hormones linked to stress and appetite. Finally, participants were given photos of 24 snack food items like chocolate and another 24 items that weren’t edible at all, like a hat or coffee mug. They were then asked how much they were willing to pay for each item. 

Another experiment within the study examined brain activity through a functional magnetic resonance imaging (fMRI) scan, while participants were asked to choose whether or not they would buy these same items at fixed prices. One week, one group of participants would do this after sleeping at home and the next, they’d do so after staying at the laboratory and vice versa. 

Data showed that when participants had stayed the night at the laboratory and were sleep deprived, they were more likely to pay more for snack foods than when rested. Tests also showed they had higher levels of a substance called des-acyl ghrelin in their blood, which is related to the “hunger hormone” ghrelin. Meanwhile, the fMRI results showed that sleep-deprived participants had greater brain activity in the amygdala —the region of the brain that processes food as a reward — when shown food images. 

Throughout all of this, whether sleep deprived or not, all participants were consistently similarly hungry when tested and surveyed in the morning, and blood sugar and hormone levels were similar among both groups as well. Researchers said that they’re not sure what creates changes in activity in the amygdala and hypothalamus, concluding that more than just hormone levels from lack of sleep were at play. “We know that changes in other neurotransmitters such as dopamine occur following sleep deprivation, so this might be another candidate,” said Peters.

According to Christian Benedict, an unassociated neuroscientist at Uppsala University says the findings make sense. Benedict points out that sleep-deprivation requires the brain to use more energy, and promoting signals that might increase the consumption of any energy source would be a logical next step. And from this perspective, impulse control is almost antithetical to survival altogether. But he also pointed to potential shortcomings in the research, like the fact that participants weren’t also given photos of healthy foods as a control for monitoring brain activity and responses. “It is not only about sleep. Physical activity matters, dietary things, food, and accessibility. So we should not break it down only to sleep.”

But of course, a lack of sleep has far wider reaching impacts on our health than simply what we choose to eat the next day. It’s a vicious cycle that’s hard to break. After about 19 hours without sleep, your brain starts to function significantly slower. Your reaction time, attention, memory, and mental accuracy all drop significantly — the equivalent of having a blood alcohol concentration of 0.05 percent. Round it out to a full 24 hours without sleep and that brain function is on par with somebody who is legally drunk with a 0.08 BAC. This is because while you’re sleeping, your brain is busy cleaning away and flushing out cellular waste, prepping you for quicker mental processing and even a better mood. As for the rest of your body, muscles recover and fat is burned while you’re asleep. Testosterone and growth hormone levels drop, impairing your protein synthesis so you struggle to build more muscle when you get poor sleep or inconsistent sleep. When cortisol levels rise, fat storage rises as well and muscle mass starts to break down. 

“I think sleep is honestly one of the greatest biohacks and the biggest performance-enhancing thing that you can do,” says sleep expert and Oura Ring creator Harpreet Rai. “Sleep is the foundation of our health and the foundation of our body and mind.”