A few cheat days every month are harmless, right? Apparently not. At least, this is what a seminal 2025 paper in Nature Metabolism says.
Researchers at the University of Tübingen found that 5 days of overeating, namely an excess of 1,500 calories per day most of which was in the form of ultra-processed snacks, was enough to cause some impairment in brain function.
This effect was seen even in healthy, young men with normal body weight.
Highlights:
- 🧠 Decreased brain white matter integrity, especially in those parts involved in reward and decision-making processes.
- 💉 Disrupted brain insulin responsiveness, even after returning to a normal diet.
- 😣 Decreased reward sensitivity and increased punishment sensitivity, the brain was less motivated by rewards and more responsive to negative outcomes.
- 🏥 Increased liver fat, without any significant weight gain or change in body fat composition.
The changes were persistent, a couple of effects on brain functions were still evident a full week after the subjects went back to their normal diet.
Why It Matters:
Insulin is not just about blood sugar. In the brain, insulin regulates appetite, reward learning, and cognition such as memory.
When insulin action in the brain is impaired, a state that some researchers are calling “brain insulin resistance,” it can potentially increase the risk for obesity, metabolic syndrome, and even neurodegenerative diseases like Alzheimer’s.
And the scary part? These detrimental effects could set in before the initially visible sign of weight gain.
Bottom line:
A couple of days spent binge eating ultra-processed snacks could seem benign enough, but this study highlights how it can actually rewire your brain quickly and silently.
The brain’s capacity to process rewards, make decisions, and regulate hunger could be affected longer than the few days of overeating.
So you might want to think twice next time you plan a cheat week, not just for the waistline but also for the mind.