If you eat healthy six days out of the week, you’re allowed to go crazy on the seventh, right? Not exactly: Just one day of binge eating on high fat food can mess with your body, a new study in the journal

In the study, researchers recruited 15 healthy volunteers and gave them a pretty pleasant task: For one day, eat a diet full of tasty, high fat foods—like sausage, bacon, fried eggs, burgers, and cheesecake—totaling 78 percent more total calories than their normal daily requirement. Then, they measured their blood sugar readings and compared it to their levels before their feast.

The results? One day of high-fat bingeing decreased their whole-body insulin sensitivity by 28 percent. Insulin sensitivity refers to how sensitively your body reacts to insulin, a hormone that allows your cells to absorb blood sugar from the blood and use it for energy.

If you’re insulin sensitivity is diminished, your body may need more and more insulin to help absorb the blood sugar. Eventually, your pancreas may be unable to crank out enough insulin to complete the task, so the excess blood sugar will begin to build up in your blood stream. That can lead to prediabetes or diabetes down the line.

This findings of this study show that just one day of overeating fatty foods can mess with your body’s ability to process sugar effectively.

“Sustained over-production of insulin—by the pancreas—can lead to pancreatic dysfunction and an inability to produce insulin when it is needed,” study author Carl Hulston said in a statement.

Now, there are a couple of caveats: First, because of how the study was designed, the researchers can’t tell for sure what part of the diet was the problem. Was it the greater number of calories overall? The higher percentage of fats? Or a combination of the two?

Secondly, while the findings show an acute disruption in the body’s insulin sensitivity, the researchers don’t exactly know the health implications of it. For instance, they didn’t study whether the effects persisted after returning to a more regular eating pattern, and if continual periods of binge eating lead to a progressive worsening of insulin measures.

So more research is needed to explore those avenues more deeply. Still, the researchers do believe the effects that they noticed would likely be compounded in groups more at risk of type 2 diabetes—say, those who are overweight and sedentary.