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How Just Five Days Of Ultraprocessed Foods Can Disrupt Your Brain
We've all had those weeks—holidays, vacations, a stressful period filled with takeout—where we indulge in calorie-laden, ultraprocessed foods. But what if just five days of overeating could have lasting effects on your brain's insulin response?
A recent study1 suggests that even short-term indulgence in high-caloric, sugary, and fatty foods can impair brain insulin function long after you stop the unhealthy eating streak. And the kicker? These effects occur even before noticeable weight gain.
Brain insulin: The hidden metabolic regulator
We often associate insulin with blood sugar control, but this hormone plays a crucial role in the brain as well. Normally, insulin acts on the brain to suppress appetite, regulate metabolism, and maintain cognitive function.
However, when the brain becomes resistant to insulin—something commonly seen in obesity and Type 2 diabetes—these functions are disrupted, leading to increased fat accumulation, metabolic disorders, and even cognitive impairments.
What the study found
Researchers set out to investigate how a short-term, high-caloric diet affects brain insulin responsiveness. The study involved 29 healthy-weight men aged 19–27 years. Eighteen participants followed a five-day diet that included an additional 1,500 calories per day of ultraprocessed snacks, while the control group maintained their regular diet.
Using intranasal insulin (a method that directly delivers insulin to the brain) and functional MRI scans, the researchers measured how the brain responded before, during, and after the dietary intervention. The results were eye-opening:
- Brain insulin activity initially increased in reward-related regions, suggesting a heightened response to the influx of sugary and fatty foods.
- Liver fat content significantly increased, even though there was no immediate change in body weight.
- Reward learning was impaired, making participants more sensitive to punishment and less responsive to positive reinforcement—a shift commonly observed in obesity.
- One week after returning to a normal diet, brain insulin response in cognitive-related regions (such as the hippocampus) remained diminished.
The long-lasting effects of short-term overeating
What makes these findings particularly concerning is that the negative effects on brain insulin sensitivity persisted even after participants resumed their regular diet.
While the brain initially showed an exaggerated response to insulin in food-reward pathways during the overeating phase, cognitive-related brain regions (like the hippocampus and fusiform gyrus) showed reduced insulin sensitivity even after the diet ended. This could have implications for memory, decision-making, and metabolic control down the line.
The study also highlights a crucial point: Brain insulin resistance can develop independently of peripheral insulin resistance. This means that even if your blood sugar and body weight remain stable, your brain's metabolism might still be taking a hit from short-term indulgence in ultraprocessed foods.
Implications for long-term health
While this study focused only on young, healthy-weight men, previous research suggests that brain insulin sensitivity declines with age and may be influenced by hormonal factors—particularly in women.
These findings add to growing concerns about how habitual consumption of ultraprocessed foods could prime the brain for insulin resistance, potentially contributing to obesity, metabolic disorders, and even neurodegenerative diseases like Alzheimer's.
The takeaway
So, what does this mean for the average person?
While the occasional indulgence won't wreak havoc, habitual overeating of ultraprocessed, high-caloric foods could have lasting consequences, beyond just weight gain. The study suggests that our brains adapt quickly to dietary changes but not always in a beneficial way.
The good news? While the effects of an unhealthy diet can linger, sustained healthy eating habits can help reverse them over time.