As baseball season approaches, I’m getting excited to see our local minor league team hit the field. I’m also looking forward to spending a fun day at the game with friends and family. And, of course, part of that fun includes more junk food than I would normally eat, just like most of us do at a ballgame. A hot dog with extra mustard, a hamburger (or Impossible burger for my vegan friends), some fries, cotton candy, and several sugary drinks—it’s all part of the ballpark experience. Heck, even baseball’s unofficial anthem tells us to “buy me some peanuts and Cracker Jack.” Written in 1908, this almost sounds healthy compared to today’s typical ballpark feast.

One day of overindulgence might not be so bad, but what if that game is the day before Independence Day? Then there are those back-to-back family picnics, barbecues, and long summer nights filled with ice cream, chips, and other high-caloric treats. Still, no harm done if it’s just for a few days, right?

Wrong. According to a recently published study in Nature Metabolism [1], even a short-term binge on high-caloric foods can cause significant changes in brain activity. The type of changes that persist even after returning to a normal diet. Worse yet, these changes resemble patterns seen in people with obesity, even though the participants in this study didn’t gain weight. A junk-food binge can affect your brain long before it shows up on your waistline.

Researchers at the University of Tübingen in Germany recruited 29 healthy young men and split them into two groups. One group maintained a regular diet, while the other consumed an extra 1,500 calories per day for five days, primarily by consuming ultra-processed, high-fat, high-sugar snacks.

At three different time points—before the diet change, immediately after, and one week later—researchers used functional MRI (fMRI) scans to measure the participants’ brain activity. But they didn’t simply measure brain activity in a resting state; they also administered insulin via a nasal spray. You might be wondering, “Why insulin?” Well, insulin, a hormone, doesn’t just regulate blood sugar; it also impacts the brain’s ability to control appetite and food consumption. When insulin signaling in the brain is disrupted, people tend to eat more and struggle with regulating their appetite.

After the five-day binge, the “junk food” group showed increased activity in brain regions involved in food reward and dietary changes. They experienced a pattern that mirrors what is seen in individuals experiencing obesity and insulin resistance.

One week after returning to a normal diet, the same participants showed reduced activity in brain regions linked to memory and visual food cues. In other words, the effects of the high-caloric diet outlasted the binge itself. This suggests that even short-term overeating can disrupt or impact how the brain responds to food, potentially making it harder to regulate eating behavior in the long term.

Consider this: You know that sluggish, foggy feeling that lingers after a weekend of too much junk food? Or how junk food can feel weirdly addictive? This study provides a potential explanation for why that might be happening from a neuroscientific perspective.

The brain adapts quickly to what we eat, and even a brief period of too much junk food can shift insulin activity in ways that resemble early markers of metabolic dysfunction. While these effects might not be permanent, they could make it tougher to resist cravings and regulate food consumption over time.

So, the next time you reach for that extra-large serving of fries, it’s worth considering not just how it might make you feel physically or what it might do to your waistline but also how it could influence your brain’s response to food in the days to come.

Remember: The brain remembers what you eat.