It feels good to have a little bit of junk food now and then. You just can’t do it too often.

That seems like common sense, but new research suggests that even just five days’ worth of junk food is enough to radically affect insulin sensitivity in the brain, directly leading to the development of obesity.

A study from the University of Tübingen in Germany found that after just five days of eating an extra 1,500 calories that come from junk food like potato chips and chocolate, insulin sensitivity in the brains of study participants dropped. Insulin regulates appetite. It tells the brain when to reduce food intake.

In the brains of the obese, insulin isn’t as effective, which causes insulin resistance and leads to unhealthy weight gain and associated medical issues like diabetes.

Eating Junk Food For Just Five Days Can Put You Down The Path Toward Obesity

While no one part of the study showed signs of significant weight gain during the five days, the researchers did notice a big jump in liver fat, demonstrating that in just five days the body was already responding negatively to the sudden glut of fatty, ultra-processed foods.

The researchers also noticed that the effects could linger even after the participants reverted to their normal diets. Just five days of eating poorly can set you down the path toward obesity. All of this suggests that there’s a lot more at play in the development of obesity than overeating or inactivity.

A lot of it could revolve around how the brain adapts to dietary changes. Even then, some people are naturally more resistant to insulin, thus leading to more insatiable appetites and more weight gain.

The lesson here is that you should make sure to limit those high-caloric days where you release your inhibitions and pig out like you don’t have a care in the world. Those cheat days can easily turn into cheat weeks that can set you up for long-term insulin resistance that can create a feedback loop of insatiable hunger.