Three weekly servings of French fries linked to higher diabetes risk
But similar amounts of boiled, baked and mashed potatoes are not associated with a substantially increased risk, say researchers
BMJ Group
Eating three servings of French fries a week is associated with a 20% increased risk of developing type 2 diabetes, but eating similar amounts of potatoes cooked in other ways - boiled, baked or mashed - does not substantially increase the risk, finds a study published by The BMJ today.
What’s more, replacing any form of potatoes with whole grains was associated with a lower type 2 diabetes risk, but swapping them for white rice was linked to an increased risk, the results show.
Potatoes contain several nutrients including fibre, vitamin C, and magnesium, but they also have a high starch content and therefore a high glycemic index, so have been linked to a higher risk of developing type 2 diabetes.
But neither the preparation method for potatoes nor specific foods that potatoes would replace have been considered, both of which are key to evaluating the overall health impact of potatoes.
To address this, researchers investigated the association between intake of potatoes prepared by different methods (boiled, baked, or mashed versus French fries) and risk of type 2 diabetes. They also looked at the impact on health of replacing potatoes with other major carbohydrates, such as whole grains and rice.
Their findings are based on more than 205,000 health professionals from three large US studies carried out between 1984 and 2021. Participants were free of diabetes, heart disease or cancer and completed detailed food questionnaires every four years.
During almost 40 years of follow up, 22,299 people were diagnosed with type 2 diabetes.
After adjusting for lifestyle and dietary factors related to diabetes risk, the researchers found that for every three weekly servings of total potato, the rate of type 2 diabetes increased by 5% and for every three weekly servings of French fries, the rate increased by 20%. However, similar intake of baked, boiled, or mashed potatoes was not associated with a significantly increased risk.
Replacing three weekly servings of total potato with whole grains lowered the type 2 diabetes rate by 8%. Substituting baked, boiled, or mashed potatoes with whole grains lowered the rate by 4%, and replacing French fries lowered the rate by 19%.
In contrast, replacing total potatoes or baked, boiled, or mashed potatoes with white rice was associated with an increased risk of type 2 diabetes.
This is an observational study so no firm conclusions can be drawn about cause and effect and the researchers can’t rule out the possibility that other unmeasured factors may have influenced their results. Most participants were also health professionals of European ancestry, so findings may not apply to other populations.
Nevertheless, they conclude: “Our findings underscore that the association between potato intake and type 2 diabetes risk depends on the specific foods used as replacement. The findings also align with current dietary recommendations that promote the inclusion of whole grains as part of a healthy diet for the prevention of type 2 diabetes.”
So, are potatoes back on the plate? Well, it depends, say researchers in a linked editorial, who note that it is important to consider preparation method and replacement food when guiding the public or informing policy.
They point out that with their relatively low environmental impact and their health impact, baked, boiled, or mashed potatoes can be part of a healthy and sustainable diet, though whole grains should remain a priority, but say future studies from more diverse populations that account for both preparation methods and substitution analysis are needed.
Journal
BMJ
Article Title
Total and specific potato intake and risk of type 2 diabetes: results from three US cohort studies and a substitution meta-analysis of prospective cohorts
Article Publication Date
6-Aug-2025
Potatoes may increase risk of type 2 diabetes—depending on their preparation
Peer-Reviewed Publication Key points:
- In a study that tracked the diets of more than 205,000 adults over decades, three servings weekly of French fries was associated with a 20% excess risk of developing type 2 diabetes (T2D). There was no significant association between consumption of baked, boiled, or mashed potatoes and risk of diabetes. However, swapping any form of potatoes for whole grains was estimated to lower T2D risk.
- The study offers the most comprehensive findings on potatoes and T2D risk to date. Prior studies have not examined the effects of replacing potatoes with other foods.
- According to the researchers, the findings can inform individuals looking to make healthier food choices and policymakers considering national dietary guidelines.
Boston, MA—French fries were associated with an increased risk of developing type 2 diabetes (T2D), while other forms of potatoes—including baked, boiled, and mashed—were not, according to a new study led by Harvard T.H. Chan School of Public Health. The study also found that swapping any form of potato for whole grains may lower the risk of T2D.
The study will be published July 30 in the BMJ.
According to the researchers, while previous studies hinted at a link between potatoes and T2D, the evidence was inconsistent and often lacked detail on cooking methods and the potential effects of substituting other foods for potatoes. “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,” said lead author Seyed Mohammad Mousavi, postdoctoral research fellow in the Department of Nutrition. “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?”
The researchers examined the diets and diabetes outcomes of 205,107 men and women enrolled in the Nurses’ Health Study, Nurses’ Health Study II, and Health Professionals Follow-up Study. For more than 30 years, participants regularly responded to dietary questionnaires, detailing the frequency with which they consumed certain foods, including French fries; baked, boiled, or mashed potatoes; and whole grains. They also reported on new health diagnoses, including T2D, and various other health, lifestyle, and demographic factors, which the researchers controlled for. Over the course of the study period, 22,299 participants reported that they developed T2D.
The study found that three servings weekly of French fries increased the risk of developing T2D by 20%. Baked, boiled, and mashed potatoes were not significantly associated with T2D risk. The researchers calculated, however, that eating whole grains—such as whole grain pasta, bread, or farro—in place of baked, boiled, or mashed potatoes could reduce the risk of T2D by 4%. Replacing French fries with whole grains could bring T2D risk down by 19%. Even swapping refined grains for French fries was estimated to lower T2D risk.
The researchers complemented their study with a novel meta-analytic approach to estimate how swapping potatoes for whole grains could affect the risk of T2D, using data from previously published cohort studies. 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 over 500,000 participants and 43,000 T2D diagnoses across four continents. The results were closely consistent with those of the new study.
“The public health message here is simple and powerful: Small changes in our daily diet can have an important impact on risk of type 2 diabetes. Limiting potatoes—especially limiting French fries—and choosing healthy, whole grain sources of carbohydrate could help lower the risk of type 2 diabetes across the population,” said corresponding author Walter Willett, professor of epidemiology and nutrition. “For policymakers, our findings highlight the need to move beyond broad food categories and pay closer attention to how foods are prepared and what they’re replacing. Not all carbs—or even all potatoes—are created equal, and that distinction is crucial when it comes to shaping effective dietary guidelines.”
Other Harvard Chan co-authors included Xiao Gu, Hala AlEssa, Qi Sun, Frank Hu, JoAnn Manson, and Eric Rimm.
The study was supported by the National Institutes of Health (grants UM1 CA186107, U01 CA176726, and U01 CA167552); the Friends of FACES/Kids Connect; the Medical Research Council Epidemiology Unit (grant MC_UU_00006/3); the UK National Institute for Health and Care Research Biomedical Research Centre Cambridge Theme on Nutrition, Obesity, Metabolism and Endocrinology (grants NIHR203312, NIHR202397); and the Kuwait Heart Foundation.
“Total and specific potato intake and risk of type 2 diabetes: results from three US cohort studies and a substitution meta-analysis of prospective cohorts,” Seyed Mohammad Mousavi, Xiao Gu, Fumiaki Imamura, Hala B. AlEssa, Orrin Devinsky, Qi Sun, Frank B. Hu, JoAnn E. Manson, Eric B. Rimm, Nita G. Forouhi, Walter C. Willett, The BMJ, July 30, 2025, doi: 10.1136/bmj-2024-082121
Visit the Harvard Chan School website for the latest news and events from our Studio.
###
Harvard T.H. Chan School of Public Health is a community of innovative scientists, practitioners, educators, and students dedicated to improving health and advancing equity so all people can thrive. We research the many factors influencing health and collaborate widely to translate those insights into policies, programs, and practices that prevent disease and promote well-being for people around the world. We also educate thousands of public health leaders a year through our degree programs, postdoctoral training, fellowships, and continuing education courses. Founded in 1913 as America’s first professional training program in public health, the School continues to have an extraordinary impact in fields ranging from infectious disease to environmental justice to health systems and beyond.
Key points:
- In a study that tracked the diets of more than 205,000 adults over decades, three servings weekly of French fries was associated with a 20% excess risk of developing type 2 diabetes (T2D). There was no significant association between consumption of baked, boiled, or mashed potatoes and risk of diabetes. However, swapping any form of potatoes for whole grains was estimated to lower T2D risk.
- The study offers the most comprehensive findings on potatoes and T2D risk to date. Prior studies have not examined the effects of replacing potatoes with other foods.
- According to the researchers, the findings can inform individuals looking to make healthier food choices and policymakers considering national dietary guidelines.
Boston, MA—French fries were associated with an increased risk of developing type 2 diabetes (T2D), while other forms of potatoes—including baked, boiled, and mashed—were not, according to a new study led by Harvard T.H. Chan School of Public Health. The study also found that swapping any form of potato for whole grains may lower the risk of T2D.
The study will be published July 30 in the BMJ.
According to the researchers, while previous studies hinted at a link between potatoes and T2D, the evidence was inconsistent and often lacked detail on cooking methods and the potential effects of substituting other foods for potatoes. “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,” said lead author Seyed Mohammad Mousavi, postdoctoral research fellow in the Department of Nutrition. “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?”
The researchers examined the diets and diabetes outcomes of 205,107 men and women enrolled in the Nurses’ Health Study, Nurses’ Health Study II, and Health Professionals Follow-up Study. For more than 30 years, participants regularly responded to dietary questionnaires, detailing the frequency with which they consumed certain foods, including French fries; baked, boiled, or mashed potatoes; and whole grains. They also reported on new health diagnoses, including T2D, and various other health, lifestyle, and demographic factors, which the researchers controlled for. Over the course of the study period, 22,299 participants reported that they developed T2D.
The study found that three servings weekly of French fries increased the risk of developing T2D by 20%. Baked, boiled, and mashed potatoes were not significantly associated with T2D risk. The researchers calculated, however, that eating whole grains—such as whole grain pasta, bread, or farro—in place of baked, boiled, or mashed potatoes could reduce the risk of T2D by 4%. Replacing French fries with whole grains could bring T2D risk down by 19%. Even swapping refined grains for French fries was estimated to lower T2D risk.
The researchers complemented their study with a novel meta-analytic approach to estimate how swapping potatoes for whole grains could affect the risk of T2D, using data from previously published cohort studies. 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 over 500,000 participants and 43,000 T2D diagnoses across four continents. The results were closely consistent with those of the new study.
“The public health message here is simple and powerful: Small changes in our daily diet can have an important impact on risk of type 2 diabetes. Limiting potatoes—especially limiting French fries—and choosing healthy, whole grain sources of carbohydrate could help lower the risk of type 2 diabetes across the population,” said corresponding author Walter Willett, professor of epidemiology and nutrition. “For policymakers, our findings highlight the need to move beyond broad food categories and pay closer attention to how foods are prepared and what they’re replacing. Not all carbs—or even all potatoes—are created equal, and that distinction is crucial when it comes to shaping effective dietary guidelines.”
Other Harvard Chan co-authors included Xiao Gu, Hala AlEssa, Qi Sun, Frank Hu, JoAnn Manson, and Eric Rimm.
The study was supported by the National Institutes of Health (grants UM1 CA186107, U01 CA176726, and U01 CA167552); the Friends of FACES/Kids Connect; the Medical Research Council Epidemiology Unit (grant MC_UU_00006/3); the UK National Institute for Health and Care Research Biomedical Research Centre Cambridge Theme on Nutrition, Obesity, Metabolism and Endocrinology (grants NIHR203312, NIHR202397); and the Kuwait Heart Foundation.
“Total and specific potato intake and risk of type 2 diabetes: results from three US cohort studies and a substitution meta-analysis of prospective cohorts,” Seyed Mohammad Mousavi, Xiao Gu, Fumiaki Imamura, Hala B. AlEssa, Orrin Devinsky, Qi Sun, Frank B. Hu, JoAnn E. Manson, Eric B. Rimm, Nita G. Forouhi, Walter C. Willett, The BMJ, July 30, 2025, doi: 10.1136/bmj-2024-082121
Visit the Harvard Chan School website for the latest news and events from our Studio.
###
Harvard T.H. Chan School of Public Health is a community of innovative scientists, practitioners, educators, and students dedicated to improving health and advancing equity so all people can thrive. We research the many factors influencing health and collaborate widely to translate those insights into policies, programs, and practices that prevent disease and promote well-being for people around the world. We also educate thousands of public health leaders a year through our degree programs, postdoctoral training, fellowships, and continuing education courses. Founded in 1913 as America’s first professional training program in public health, the School continues to have an extraordinary impact in fields ranging from infectious disease to environmental justice to health systems and beyond.
Journal
The BMJ
The BMJ
DOI
Method of Research
Observational study
Observational study
Subject of Research
Not applicable
Not applicable
Article Title
Total and specific potato intake and risk of type 2 diabetes: results from three US cohort studies and a substitution meta-analysis of prospective cohorts
Total and specific potato intake and risk of type 2 diabetes: results from three US cohort studies and a substitution meta-analysis of prospective cohorts
Article Publication Date
6-Aug-2025
6-Aug-2025
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