Most of us have experienced periods where we’ve eaten a little more than usual. A holiday. A long weekend. A stressful week. A celebration.
Traditionally, we’ve thought about overeating mainly in terms of weight gain. But emerging research suggests something even more interesting may be happening -changes in the brain itself.
A recent study found that just five days of consuming extra high-fat, high-sugar foods altered how healthy young adults’ brains responded to insulin, even before significant weight gain occurred. Some of these changes were still detectable after participants returned to their normal eating patterns.
So what does this mean for brain health?
Your Brain Runs on More Than Willpower
When most people hear the word insulin, they think about blood sugar or diabetes. What many don’t realise is that insulin also plays an important role in the brain.
Insulin helps regulate appetite, energy balance, reward processing and feelings of fullness. When insulin signalling is working well, the brain is better able to recognise when we’ve had enough to eat and helps regulate food-related reward pathways.
In this study, researchers found that a short period of overeating calorie-dense, highly processed foods reduced the brain’s sensitivity to insulin. Interestingly, these changes occurred in healthy young adults who were not overweight and showed no signs of metabolic disease. In other words, the brain appeared to respond to the diet before the bathroom scales did.
Why This Matters
The findings help explain why unhealthy eating patterns can sometimes feel difficult to break. When reward pathways become more responsive to highly processed foods and insulin signalling becomes less effective, cravings can increase and feelings of fullness may become less reliable. Researchers suggest this may create conditions that encourage ongoing overeating.
This doesn’t mean that five days of holiday eating will permanently damage your brain but it does remind us that our brains are constantly adapting to the environments we create for them.
Just as repeated healthy habits strengthen brain networks that support wellbeing, repeated exposure to highly processed foods may strengthen pathways that make those foods more appealing.
The good news? The brain remains remarkably adaptable throughout life.
The Bigger Picture: Brain Health Is Built Daily
One of the most important messages from this research is that brain health isn’t determined by a single meal, a single day or even a single week. What matters most is the overall pattern.
At Brainfit®, we often talk about the concept of “brain deposits”. Every day we make small deposits or withdrawals from our future brain health through the choices we make around:
- Nutrition
- Physical activity
- Sleep
- Stress management
- Social connection
- Lifelong learning
No single decision makes or breaks brain health. It’s the accumulation of small actions over time that matters most.
What To Do After a Period of Overindulgence
If you’ve recently enjoyed a holiday, celebration or indulgent weekend, resist the urge to punish yourself with extreme diets or guilt. Instead, focus on returning to your normal healthy routines:
Prioritise Protein and Plants
Aim for meals built around quality protein, vegetables, fruit, legumes and whole grains.
Move Your Body
Physical activity helps improve insulin sensitivity and supports healthy brain function.
Get Back to Consistent Sleep
Poor sleep can increase cravings and make healthy choices more difficult.
Stay Hydrated
Sometimes fatigue and cravings can be made worse by mild dehydration.
Focus on Progress, Not Perfection
A few days of less-than-ideal eating do not define your future brain health.
The Brainfit® Takeaway
Perhaps the most important lesson from this research is that the brain is listening to what we repeatedly do. Our eating habits don’t just affect our waistline; they influence the systems that regulate appetite, reward, motivation and long-term brain health.
The encouraging news is that this works both ways. Just as the brain adapts to unhealthy habits, it can also adapt to healthy ones. Every nutritious meal, every walk, every good night’s sleep and every healthy choice is another small investment in the health and resilience of your brain.
And those investments add up.
This article was inspired by recent media coverage of research published in Nature Metabolism. You can read more about it here.
References
- Kullmann S. et al. (2025). A short-term, high-caloric diet has prolonged effects on brain insulin action in healthy men. Nature Metabolism.
- Psychology Today (2026). Just Five Days of Junk Food Can Rewire the Brain.
A Note About The Research
As with many studies in neuroscience and health, the participants in this research were healthy young men. While the findings are important, more research involving women, older adults and more diverse populations is needed. Understanding how lifestyle factors affect brain health across different groups remains an important priority for future research.
