A new study has found that just five days of eating a high-calorie, ultra-processed diet can impair brain function and increase liver fat, even in healthy young men.
Researchers at the Institute for Diabetes Research and Metabolic Diseases in Germany discovered that these short-term effects can last beyond the period of overeating, potentially influencing long-term eating behaviors.
How Overeating Affects the Brain and Liver
The study, published in Nature Metabolism, involved 29 healthy men aged 19–27 with normal weight. Eighteen participants were assigned to a high-calorie diet (HCD) group, where they consumed an extra 1,500 calories per day from processed snacks.
The remaining 11 participants followed their usual diet as a control group. To ensure accurate results, all participants were restricted to fewer than 4,000 steps per day to limit physical activity.
By the end of the five-day period, the HCD group had increased their daily calorie intake by about 1,200 calories. While their body weight did not change significantly, their liver fat content rose from 1.55% to 2.54%, whereas the control group showed no changes.
Brain insulin responsiveness, which plays a crucial role in appetite and metabolism, was also affected. Insulin resistance in the brain has been linked to obesity, type 2 diabetes, and cognitive decline.
Using brain scans and intranasal insulin administration, researchers found that while certain brain regions showed an initial increase in insulin response after the diet, key cognitive areas showed reduced responsiveness one week after returning to a regular diet.
Overeating Affects Reward Processing and Decision-Making
Another significant finding was the impact of overeating on the brain’s reward system, which influences motivation and decision-making. Researchers tested participants using a “go/no-go” task, which measures how well the brain responds to rewards and punishments.
After five days of consuming high-calorie snacks, participants in the HCD group showed reduced sensitivity to rewards, meaning they found positive outcomes less motivating. At the same time, they had an increased sensitivity to punishment, indicating a heightened negative response to mistakes or setbacks.
These changes are similar to patterns seen in people with obesity, suggesting that even a short period of overeating can alter brain function in ways that may encourage unhealthy eating habits in the future.
Long-Term Implications
Although some effects showed signs of reversing after participants resumed their normal diet, they did not fully return to baseline within a week. This raises concerns about whether repeated short-term periods of overeating could lead to lasting changes in brain function, making it harder to regulate food choices and maintain a healthy diet over time.
The study highlights the importance of dietary habits beyond just weight gain. While overeating for a few days may not immediately affect body weight, it can still disrupt brain function, insulin response, and liver health.
These findings suggest that limiting ultra-processed, high-calorie foods is crucial for maintaining not only physical health but also cognitive and metabolic well-being.
The research findings can be found in Nature Metabolism.
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