Saint Louis University researchers say that eating too much fast food–a diet high in fat and sugar–can cause serious damage to the liver in as little as a week.

In mice, just one month on a diet that mimicked fast food resulted in an increase in liver enzymes–a key indicator of liver damage–and the beginnings of glucose intolerance, they found. In another study by researchers in Sweden’s University Hospital of Linkoping, people who ate fast food and were sedentary for a month began to have a sharp rise in liver enzymes within a week.

To reverse this damage, the researchers say to limit fast-food (high-calorie, high-fat) restaurant visits to no more than once a week, choose the healthiest options, exercise regularly, and have key liver enzymes measured regularly.

Saint Louis University Medical Center News Release