French fries are a staple of the American diet, for better or worse. Thomas Jefferson, the third U.S. president, is often credited with helping popularize them in America after enjoying the delicacy as U.S. minister to France in the 1780s.

He’s also sometimes recognized for promoting ice cream and a rudimentary mac-and-cheese dish. So, if overindulgence in these foods has expanded your waistline, you might blame the Founding Father.

Unlike Jefferson, we now know that fries are an unhealthy dish.

Now, a large study by Harvard researchers shows that eating French fries substantially increases the risk of Type 2 diabetes. The researchers tracked 200,000 Americans over several decades and found a 20% higher risk of the disease for those who ate three extra servings of fries a week.

In contrast, scientists found no significant correlation between diabetes and the consumption of baked, boiled or mashed potatoes.

Participants filled out questionnaires about health and diet every two to four years. That amounts to more than 5 million years collectively. The group was composed of medical professionals like doctors and nurses. Why they were exclusively selected is not stated in the study. But medical professionals are considered reliable and accurate in self-reports, which in turn makes the data more reliable.

Researchers found diabetes risk dropped 19% if those three extra servings of French fries were swapped with whole grains, such as brown rice or oats.

The biggest contributor to risk appeared to be weight gain, since the fry aficionados tended to put on the pounds.

So, don’t be Thomas Jefferson. Skip the fries. Grab a baked potato, or better yet some brown rice.