If you're a big fan of French fries, you might want to take a second look at what's landing on your plate. According to a new study from Harvard T.H. Chan School of Public Health, your favorite potato side dish may come with a side of health risk.

Specifically, there's a 20 percent increased chance of developing type 2 diabetes (T2D) if you're indulging in three or more sides of fries in a week.

There's no reason to ban all potatoes just yet. Other forms of potatoes, like boiled, baked or mashed, weren't significantly linked to diabetes. The key takeaway? It's not necessarily the potato; it's how it's prepared.

Even refined grains like white bread were better than fries when it came to diabetes.

The researchers tracked the diets and health outcomes of over 205,000 men and women across three long-running studies: the Nurses' Health Study, Nurses' Health Study II and Health Professionals Follow-up Study. Over 30 years, participants reported how often they ate specific foods, including various potato dishes and whole grains. During this period, more than 22,000 participants had developed type 2 diabetes.

While French fries raised red flags, other potato forms remained in the clear. More importantly, the research team estimated that swapping potatoes — any kind — with whole grains like farro, quinoa or whole wheat bread could lower diabetes risk. Replacing fries with whole grains was projected to reduce the diabetes risk by up to 19 percent. Even refined grains like white bread were better than fries when it came to type 2 diabetes.

“Our study offers deeper, more comprehensive insights by looking at different types of potatoes, tracking diet over decades, and exploring the effects of swapping potatoes for other foods,” Seyed Mohammad Mousavi, lead author of the study and postdoctoral research fellow in the Department of Nutrition at Harvard, explained in a media release.

“We're shifting the conversation from ‘Are potatoes good or bad?' to a more nuanced — and useful — question ‘How are they prepared, and what might we eat instead?'” he added.

That question is at the heart of what makes this research so compelling. The team didn't just crunch numbers; they complemented their findings with a meta-analysis from millions of people worldwide. This involved two separate meta-analyses: one based on data from 13 cohorts examining potato intake and the other from 11 cohorts on whole grain intake, each encompassing more than 500,000 participants and 43,000 T2D diagnoses across four continents.

The results were closely consistent with those of the new study and their conclusion was clear: preparation matters, and whole grain substitution matters even more.

What does that mean for your dinner table? If you're reaching for fries three times a week, your body might be paying the price in the long run. But if you're opting for baked potato or mashed potatoes, and better yet, replacing some servings with whole grains, you're likely making a better nutritional choice.

Passing up fries might just be the simplest step you can take toward lowering your risk of type 2 diabetes.

“The public health message here is simple and powerful,” added Walter Willet, M.D., M P.H. professor of epidemiology and nutrition at Harvard and corresponding author of the study. “Small changes in our daily diet can have an important impact on the risk of type 2 diabetes. Not all carbs — or even all potatoes — are created equal.”

This study arrives at a time when conversations around carbohydrates' effect on health are more complicated than ever.

From keto to gluten-free, it's easy to lose sight of the basics. What this research brings back into focus is the importance of preparation and substitution, not restriction.

And it offers something else that is just as valuable: actionable advice. Swapping French fries for whole grain bread, brown rice or a warm bowl of farro isn't just doable, it's tasty. So, the next time you're deciding between fries and a whole grain salad, consider the long-term payoff. Passing up fries might just be the simplest step you can take toward lowering your risk of type 2 diabetes.

The study is published in The BMJ.