It turns out the way you cook your potatoes could make a real difference for your health.
A massive new study following more than 200,000 U.S. health professionals over four decades finds that eating French fries as little as three times a week is linked to a 20 percent higher risk of developing type 2 diabetes. In contrast, similar amounts of potatoes prepared by boiling, baking, or mashing do not appear to carry the same risk. The research, published in BMJ, also shows that swapping any form of potatoes for whole grains is tied to lower diabetes risk, while replacing them with white rice has the opposite effect.
French Fries Stand Out as the Risk Driver
The study pooled data from the long-running Nurses’ Health Study, Nurses’ Health Study II, and Health Professionals Follow-up Study, tracking 205,107 participants who were free of diabetes, heart disease, or cancer at the start. Over nearly 5.2 million person-years of follow-up, researchers documented 22,299 new cases of type 2 diabetes.
After adjusting for age, lifestyle, body weight, and other dietary factors, the team found:
- Every three weekly servings of total potato raised diabetes risk by 5 percent.
- Every three weekly servings of French fries raised diabetes risk by 20 percent.
- Baked, boiled, or mashed potatoes showed no significant change in risk.
“Our findings underscore that the association between potato intake and type 2 diabetes risk depends on the specific foods used as replacement,” the authors write.
Why Cooking Method Matters
Potatoes are nutrient-rich, providing fiber, vitamin C, potassium, and magnesium. But they are also high in rapidly digested starch, giving them a high glycemic index. That means they can cause sharp spikes in blood sugar and insulin levels. Frying adds another layer of concern by introducing fats, salt, and potentially harmful compounds formed at high temperatures, such as advanced glycation end products, which have been linked to inflammation and metabolic problems.
The researchers note that changes in frying oils over the years may have influenced results. In the 1980s, beef tallow was common, later replaced by partially hydrogenated oils high in trans fats, which were eventually phased out in the U.S. by 2018.
Whole Grains Help, White Rice Hurts
One unique feature of this study was the substitution analysis, which modeled what happens when potatoes are replaced with other carbohydrate-rich foods. Replacing three weekly servings of:
- Total potatoes with whole grains lowered diabetes risk by 8 percent.
- Baked, boiled, or mashed potatoes with whole grains lowered risk by 4 percent.
- French fries with whole grains lowered risk by 19 percent.
Swapping potatoes for non-starchy vegetables, legumes, or even refined grains was also linked to lower risk. But replacing potatoes with white rice increased diabetes risk. The researchers caution that substitution modeling relies on statistical estimates rather than tracking actual diet changes, but the patterns align with a large body of evidence showing benefits from whole grains.
Implications for Diet and Policy
The results add nuance to the potato debate, suggesting that not all preparations carry the same health implications. With their relatively low environmental impact compared to many other staples, baked, boiled, or mashed potatoes can still be part of a healthy and sustainable diet, especially when balanced with fiber-rich whole grains. But when it comes to French fries, moderation appears wise.
In a linked editorial, experts stress the importance of considering both cooking method and what foods potatoes are replacing in the diet when making public health recommendations. They call for more research in diverse populations to confirm the findings and to better guide dietary advice.
Bottom Line
If you love potatoes, the safest bet for your blood sugar may be to skip the fryer and serve them boiled, baked, or mashed, alongside plenty of whole grains. The evidence suggests that this small change could help reduce the long-term risk of type 2 diabetes, a condition affecting more than 500 million people worldwide.
Journal: BMJ | DOI: 10.1136/bmj-2024-082121
ScienceBlog.com has no paywalls, no sponsored content, and no agenda beyond getting the science right. Every story here is written to inform, not to impress an advertiser or push a point of view.
Good science journalism takes time — reading the papers, checking the claims, finding researchers who can put findings in context. We do that work because we think it matters.
If you find this site useful, consider supporting it with a donation. Even a few dollars a month helps keep the coverage independent and free for everyone.