Ever wonder why some people never gain weight? They don’t diet, they have never seen the inside of a gym, and they are constantly eating fast food. According to scientists, those guys may have been born without the “fat enzyme.”

The enzyme in the spotlight, MGAT2, is found in the intestines and determines the fate of our food by regulating how it is metabolized: it either makes fat go straight to your waistline, or converts it into energy.

Researchers from the University of California at San Francisco found that mice missing the gene for MGAT2 were able to feast on whatever they want without becoming overweight.

In the study, mice that had the gene knocked out were compared with a group of normal mice. When both sets of mice were fed with a low-fat diet, they grew the same way. But when the little creatures were eating tasty, high-fat foods, the experimental mice weighed 40 percent less and had 50 percent less fat than the normal mice.

Not only does decreasing MGAT activity in mice reduce their chances of gaining weight, it also prevents them from developing harmful cholesterol in their blood and other obesity-related problems.

Hopefully scientists can figure out how to manipulate this gene to create a wonder drug— so we can all go on with our all-you-can-eat buffet without any worries.