Eating too much of this favorite food could increase your diabetes risk
New research shows that eating potatoes in this form raises your risk of diabetes by 20 percent. Here's what you need to know.
You might want to think twice before you reach for that last french fry at the bottom of the bag. A new study from a team of researchers at Harvard University found that eating too many fries was associated with significantly higher risk for developing Type 2 diabetes.
In the study published in BMJ, researchers analyzed nearly four decades worth of self-reported dietary data from 205,000 nurses and health professionals, making it one of the most comprehensive studies regarding potato intake and diabetes to date. The results showed those who ate three servings of boiled, mashed or baked potatoes a week had a marginally increased Type 2 diabetes risk of 1 percent. However, respondents who ate three servings of french fries a week had 20 percent risk.
(It’s possible to reverse diabetes—and even faster than you think.)
“The big takeaway? Not all potatoes are created equally,” says Seyed Mohammad Mousavi, the lead researcher and a postdoctoral research fellow in Harvard University’s department of nutrition.
If the findings make you a bit salty, fear not: There are some caveats that might put your mind at ease. So do you need to be worried if you only eat fries occasionally—or if you prefer the sweet potato kind? And if you’re going to keep eating french fries anyway, is there anything you can do to modify diabetes risk? National Geographic put these questions to the experts.
Why are potatoes a top suspect for diabetes?
Scientists have suspected for years that white potatoes could increase our risk of Type 2 diabetes. That’s because when our bodies break down potato starch, it quickly converts into glucose that enters our bloodstream and can cause our insulin to spike.
To learn more about this relationship, Mousavi’s team built upon a 2015 study that had previously looked at this question using the same survey data. This time however, the BMJ study followed participants for a longer period and included 7,000 respondents with new cases of Type 2 diabetes. Mousavi’s study also conducted an additional meta-analysis of similar research worldwide. “That allowed us to cut through the noise and show that the increased risk of diabetes really centers on French fries, not all potatoes,” Mousavi says.
Last Chance - Save up to $20!
(Scientists finally know where potatoes come from—and the answer is very weird.)
Pratik Pokharel, a postdoctoral fellow at the Danish Cancer Institute, who was not part of the study, says the research tracks with his team’s own potato findings. “Higher consumption of potato fries was associated with poorer glucose tolerance and reduced insulin sensitivity. These effects, over time, could increase the risk of developing Type 2 diabetes.”
Do I need to be worried if I only eat fries once a week?
The study defined a serving of french fries as about 4 to 6 ounces, or roughly a medium to large McDonald’s fries. Three servings a week is where scientists identified the 20 percent increase in diabetes risk.
As we know, however, people don’t always stick to recommended serving sizes—particularly in the United States. “We supersize everything,” says Walter Willett, the study’s co-author and a professor of epidemiology and nutrition at Harvard’s T.H. Chan School of Public Health. So if you’re eating one heaping pile of fries once a week, you might still need to listen up.
(Diet soda might be making you hungrier.)
Portioning can help. Johanna Lampe, a registered dietician and experimental nutritionist at the Fred Hutchinson Cancer Center, argues potatoes may be easier than other foods to eyeball to make sure you have the right portion. “French fries, typically eaten as a discrete component, may be even more accurately quantified,” she says.
While no number is “safe” Mousavi says, it’s clear “the more you eat, the steeper that risk gets.”
Are sweet potato fries still safe?
While the study didn’t focus on sweet potatoes specifically, mixed research suggests they do likely have a lower glycemic index. When we break down low glycemic index foods, the glucose enters our bloodstream more gradually. Still, they’re carbohydrates, and might increase diabetes risk if eaten in large quantities, Willett says. Oil, fat, and salt also play a role in risk. Overall, more research is needed.
What can I do to lower my risk?
Knowing how much the potato is revered—it’s the third-most consumed crop, according to the International Potato Center—researchers wanted to provide people with healthy alternatives. And it turns out, Willett says, “the choices make a big difference.”
They found that replacing baked, mashed, or boiled potatoes with whole grains could decrease diabetes risk by 4 percent, while replacing french fries with whole grains decreases risk by 19 percent.
(A cure for type 1 diabetes is close)
One surprise in their findings? Swapping out boiled, baked or mashed potatoes for rice actually increased diabetes risk, likely due to the food’s high glycemic index.
If you’re not drooling over whole grains, you can start slow, says Hilary Seligman, the director of the Food Policy, Health, and Hunger Research Program at University of California, San Francisco. “Just substitute them for refined grains in the two or three products you find most palatable to start,” Seligman says. Whole grain crackers, cereal, or bread are all great options.
What do I do if I want to have fries anyway?
One caveat is that during the time the study was conducted, french fries were mostly cooked using trans fat oils, “many which are banned now,” Mousavi says. So, the topic should be revisited.
When it comes to potatoes, “the focus should be on healthier preparation,” Pokharel says.
Think baked french fries with olive oil. What about air-frying? Mousavi says, “While we didn’t compare air-frying directly, it likely poses a lower risk than traditional deep-frying—but more studies are needed.”
Or start with baby steps. Get a side salad with your burger next time. And opt for smaller portions, Mousavi advises. “The big takeaway is that small everyday choices really do add up.”
