Obesity is one of the most common health problems among modern people. However, since the process of weight gain is often gradual, many people only suddenly realize they are fat when there are obvious changes in their body shape. This also gives some people a lucky mentality: since it takes a certain amount of time to gain weight, it's okay to indulge in overeating for a short period and then return to a healthy diet.

But a recent paper in "Nature - Metabolism" may dispel this idea. Scientists from the University of Tübingen in Germany and the German Diabetes Research Center found that when volunteers continuously consumed a high - calorie diet for only 5 days, a large amount of fat would accumulate in the liver. More significantly, the individual's brain's response to insulin would be disrupted and adapt to the short - term dietary changes. This means that as long as one fails to control their diet for a while, the brain will maintain a negative insulin response for a long time, which lays a hidden danger for future obesity.

According to the paper, the researchers recruited a total of 29 healthy male volunteers for the experiment, with a body mass index between 19 and 25. One group maintained a normal diet, while the other group needed to consume high - calorie foods for 5 days, which was equivalent to an additional 1500 kilocalories on top of the normal diet. The food types included various ultra - processed snacks, such as potato chips and chocolate. The researchers followed up with all the individuals and collected data after 5 days. Subsequently, the volunteers in the experimental group returned to their regular diet and were followed up again after one week.

The researchers found that although the volunteers in the experimental group had a rapid increase in calorie intake within 5 days, there were no significant changes in their body weight and body fat distribution. However, the analysis results showed that the liver fat content of the volunteers in the experimental group increased significantly, while there was basically no change in the control group. The accumulation of liver fat is an early sign of fatty liver, which is closely related to metabolic diseases such as insulin resistance and type 2 diabetes. In other words, although the body weight remained unchanged, the body's internal organs had already started to "sound the alarm".

On the other hand, the researchers also delivered insulin to the volunteers' bodies through nasal spray. Insulin can enter the brain via the nose - brain pathway and affect brain activities. Subsequently, the researchers used functional magnetic resonance imaging (fMRI) technology to observe the brain's response. The results showed that after only 5 days of indulgent eating, the regions in the volunteers' brains related to food reward and appetite regulation, such as the right insular cortex and the right midbrain/pons, had a significantly enhanced response to insulin. This means that the brain's "craving" for high - calorie foods became stronger.

One week after they returned to a normal diet, the responses of the hippocampus and fusiform gyrus to insulin decreased significantly. These brain regions could originally actively perform memory and learning functions under the stimulation of insulin, but the high - calorie diet changed this trend, potentially laying a hidden danger for cognitive decline.

In addition to the changes in insulin response, the study also found that a high - calorie diet would affect the brain's "decision - making system". Specifically, after 5 days, the volunteers in the experimental group became less sensitive to rewards and more sensitive to punishments. This means that they may find it more difficult to get satisfaction from healthy foods and are more likely to be tempted by high - calorie foods. This change still existed even one week after they returned to a normal diet, but the degree of influence would be reduced.

These results all indicate that even a short - term dietary indulgence can have a profound impact on the brain and body's metabolic health. Once one has the idea that "it doesn't matter to eat a little more occasionally", it will be more difficult to resist high - calorie foods in the future. To avoid obesity, the best way is to stay away from high - calorie foods and eliminate their negative impacts at the root.