Every now and then, I love a good weekend of indulgence. You know, the kind when you go on a little weekend getaway with your gals and bring out all the chips and dip and order pizzas and beer. And hey, there's totally no shame in getting greasy once in a while. But when that treat-yourself day turns into a week, things can get dicey. According to a recent study published in Nature Metabolism, just five days of consuming junk food can significantly change your brain activity. And those changes don't just revert back to normal once you return to your typical eating routine.
The study followed 29 healthy young men over five days—half of whom maintained a regular diet and half who consumed an extra 1,500 calories per day, mostly comprised of ultra-processed snacks and junk food. Throughout the study, functional MRI (fMRI) scans measured the participants' brain activity. They found that those who consumed extra junk food had similar brain activity as individuals who struggle with obesity and insulin resistance. The results also showed an increase in liver fat. And these changes didn't just go away after the week-long experiment. Even after reverting to their typical diets for another week, the participants who consumed junk food showed reduced activity in brain regions linked to memory and visual food cues.
So, How Exactly Does Junk Food Alter The Brain?
Even though the study was small and only followed men, the findings mimicked similar research conducted on mice, driving home the fact that junk food is highly addictive. Eating a significant amount of junk food over a five-day period negatively impacts how the brain processes insulin, "a key hormone for regulating appetite and food intake," explains Dr. Meghan Garcia-Webb, M.D. Surprisingly, the findings showed that these results persisted even after participants stopped eating junk food. "They also showed up well before the 'typical' markers of unhealthy lifestyle, such as weight gain, food cravings, and insulin resistance in the body," she continues.
Often, junk food is made from processed or refined carbs, preservatives, salt, artificial sweeteners, and added colors, explains medical nutrition specialist Dr. Amy Lee. "These are ingredients that are not recognized by the body and can be a cause of inflammation at all levels, including the brain," she says.
Another finding is that those who ate junk food also showed a decrease in sensitivity to rewards and an increase in sensitivity to punishments, "a pattern that is in line with some theories of addiction," says Garcia-Webb. When the brain requires more of something to get a reward, this typically indicates an addictive pattern. "Here, we have more tangible data that backs up how people often feel in real life—that junk food is addictive," Garcia-Webb explains. And that's just the tip of the iceberg. Previous studies have found an association between ultra-processed foods and negative impacts on mental health, most notably anxiety and depression.
In particular, Lee cautions consumers to be mindful of what their children eat. "I do feel that young kids and adults should avoid [junk food] as the brain is still developing," she notes. As she explains, the earlier your brain is exposed to junk food's addictive qualities, the sooner the body acclimates and begins storing the "key ingredients" that can cause a negative heath impact.
Can You Consume Junk Food Safely?
The participants in the junk food group consumed an extra 1,500 calories daily from ultra-processed snacks and experienced adverse effects. But you don't need to nix high-caloric processed foods from your diet altogether. After all, junk food is delicious. Physician Dr. Jesus L. Lizarzaburu explains, "As time has gone on and our quality of life has improved, we have forgotten that high caloric ultra-processed food are to be enjoyed occasionally and not as frequent as we seem to indulge nowadays."
He recommends paying attention to serving size when indulging in junk food. "If you are going to indulge, make it a smaller size," he says. Plus, decrease the frequency with which you consume these foods. Garcia-Webb similarly recommends limited quantities per week. And if you do want to indulge, she says to go for the highest quality available. "For example, a cookie from a great bakery (or a cookie you make yourself) is going to have fewer, better ingredients and likely be more satisfying than a cookie that comes in a package that can last on shelves for months and is loaded with preservatives," she explains.
And don't forget to couple it all with an overall healthy diet. "Make sure your daily food is for the most part fresh and minimally processed," explains Lizarzaburu. "Enjoy more fruits and vegetables. That way, you can have the treats we all crave from time to time."
