Potatoes have spent decades on the “foods to limit” list for anyone managing or trying to prevent type 2 diabetes. But a landmark study from Harvard T.H. Chan School of Public Health, published in The BMJ and re-surfaced by ScienceDaily in June 2026, suggests that the entire conversation about potatoes has been pointed at the wrong target.
It is not the potato. It is the fryer.
Researchers tracked 205,107 men and women across three of the longest-running nutrition studies in history, the Nurses’ Health Study, Nurses’ Health Study II, and the Health Professionals Follow-up Study, for nearly 40 years. Participants filled out detailed dietary questionnaires every four years, creating one of the most comprehensive long-term pictures of diet and disease ever assembled.
The finding that made headlines: eating three servings of french fries per week was linked to a 20% higher risk of developing type 2 diabetes. Baked, boiled, and mashed potatoes, eaten in the same quantities, showed no significant increase in risk.
“Not all potatoes are created equal,” said lead author Dr. Seyed Mohammad Mousavi, a postdoctoral research fellow at Harvard T.H. Chan School of Public Health. “Even a small amount of french fries, less than one serving in the week, is associated with a higher risk of type 2 diabetes.”
This article breaks down exactly what the study found, why frying changes everything, what to eat instead, and five potato recipes that keep this beloved vegetable on your plate without the risk.
The Study: 205,000 People, Nearly 40 Years
This is not a small, short-term observational study. It is one of the largest and longest nutrition studies ever conducted on this topic, and that scale is what gives its conclusions real weight.
The research combined data from three major Harvard-affiliated cohorts: the Nurses’ Health Study, the Nurses’ Health Study II, and the Health Professionals Follow-up Study. All participants were free of diabetes, heart disease, or cancer at the start of the study. Every four years, for nearly four decades, they completed detailed food frequency questionnaires that tracked how often they ate french fries, baked potatoes, boiled potatoes, mashed potatoes, and whole grains.
Over the nearly 40-year follow-up period, 22,299 participants were diagnosed with type 2 diabetes.
After adjusting for lifestyle factors and other dietary contributors to diabetes risk, the researchers calculated that for every three weekly servings of total potato intake, the rate of type 2 diabetes increased by 5%. But when they isolated french fries specifically, that number jumped to 20% for the same three-weekly-serving increase.
“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,” Dr. Mousavi explained. “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?”
This level of scale and duration is rare in nutrition science, where most studies are far smaller and shorter. It is why this research is already being cited as one of the most authoritative pieces of evidence on potato consumption and diabetes risk to date.
French Fries vs. Baked vs. Boiled vs. Mashed: The Risk Breakdown
The clearest way to understand this study is to look at how each potato preparation method compared.
| Potato Preparation | Type 2 Diabetes Risk (per 3 weekly servings) |
| French Fries | 20% higher risk |
| Total Potato Intake (all types combined) | 5% higher risk |
| Baked, Boiled, or Mashed Potatoes | No significant increase |
This table is the single most important takeaway from the entire study. The “total potato” category includes french fries, which is why it shows a modest 5% increase. But once researchers isolated french fries on their own, the risk quadrupled relative to the average. Meanwhile, the non-fried preparations, examined on their own, showed essentially no meaningful association with diabetes risk at all.
This distinction matters enormously for anyone managing blood sugar or trying to reduce their long-term diabetes medication and treatment needs through diet. A blanket “avoid potatoes” rule, which has appeared in countless diet guides for years, is not supported by this data. The preparation method, not the vegetable itself, is the determining factor.
Why Deep Frying Changes Everything
So why does frying make such a dramatic difference? The explanation comes down to chemistry and metabolism, not the potato’s natural nutritional profile.
Potatoes themselves are not nutritionally villainous. They are the third most commonly consumed crop in the world and a major source of dietary fiber, vitamin C, and magnesium. But they are also high in rapidly digestible starch, which can cause quick spikes in blood sugar, a property that has long fueled potatoes’ loose association with diabetes risk in earlier, smaller studies.
French fries take that starch profile and compound it with a second problem: the frying process itself.
“Unlike boiled or baked potatoes, french fries are deep-fried in oils that usually contain trans or saturated fats,” the researchers explained. “The way the body metabolizes those fats can contribute to insulin resistance,” a condition in which the body’s cells stop responding properly to insulin, the hormone responsible for regulating blood sugar.
Regular consumption of fried foods is also independently linked to obesity and chronic inflammation, both of which separately increase the risk of type 2 diabetes. This creates a compounding effect: the starch spikes blood sugar, the trans and saturated fats interfere with insulin signaling, and the broader pattern of fried-food consumption tends to correlate with weight gain over time. Each of these factors connects to the weight loss and obesity relationship that researchers have long identified as central to diabetes prevention.
There is also a downstream cardiovascular angle. Insulin resistance does not stay contained to blood sugar regulation alone. Over time, it contributes to the kind of metabolic dysfunction that raises heart health risk as well, making this far more than a diabetes-only concern. Emerging research on fried foods has also pointed to effects on gut health, where chronic low-grade inflammation from regular fried food intake may disrupt the gut microbiome in ways that further compound metabolic risk.
This is precisely why frequent fried-snack habits, like those examined in our piece on snacking patterns in your 40s, deserve closer attention as people move into the decades when type 2 diabetes risk begins climbing most sharply.
The Smart Swap: What to Eat Instead
The most actionable part of this study is the substitution analysis. Researchers did not just measure risk, they modeled what happens when you swap one food for another, and the results offer a clear roadmap.
Replacing french fries with whole grains (such as whole grain bread, pasta, farro, quinoa, or brown rice) was associated with an estimated 19% lower risk of type 2 diabetes.
Replacing baked, boiled, or mashed potatoes with whole grains lowered risk by a more modest 4%, reflecting the fact that these preparations were not particularly risky to begin with.
Replacing potatoes with white rice, however, had the opposite effect, increasing diabetes risk rather than lowering it. This finding alone surprised many nutrition experts, since white rice has often been treated as a neutral or even healthier starch alternative. The study suggests otherwise: white rice’s refined, low-fiber profile behaves more like a problem food than a solution in this context.
The practical takeaway is straightforward. Whole grains are the upgrade, not white rice. If you are looking for inspiration on weaving more whole grains and fiber-rich swaps into your routine, our guide to superfoods that actually work separates genuinely evidence-backed foods from wellness-industry hype, and whole grains land firmly in the “actually works” category.
For people specifically replacing fried snacks with better options throughout the day, our list of healthy snacks that help you beat junk food cravings offers practical, craving-friendly alternatives that do not require willpower alone. And if you are building a broader dietary strategy around blood sugar control, a plant-based diet rich in whole grains, legumes, and vegetables aligns closely with what this study’s substitution data recommends.
How Much Is Too Much?
This is where the study delivers its most sobering detail. There is no identified “safe” threshold for french fries based on this data.
Dr. Mousavi was direct about this: “Even a small amount of french fries, less than one serving in the week, is associated with a higher risk of type 2 diabetes.” The 20% risk figure applies to three weekly servings, but the association begins appearing at intake levels far below that.
This does not mean an occasional order of fries will derail your health. The study reflects long-term dietary patterns measured over decades, not single meals. But it does mean that french fries deserve to be treated as a genuine occasional indulgence rather than a routine weekly menu staple, which is how they function in many American diets today.
For people actively managing blood sugar or working on broader metabolic health, combining smarter potato choices with proven strategies like those covered in our guide to intermittent fasting for beginners can create a more comprehensive approach to diabetes prevention than diet changes alone.
5 Easy Potato Recipes That Won’t Spike Your Diabetes Risk
The good news from this study is that you do not need to give up potatoes. You simply need to change how you cook them. Here are five preparations backed by the study’s own findings, since none of them involve deep frying.
- Herb-Roasted Potato Wedges Cut potatoes into wedges, toss lightly in olive oil, and roast at high heat with rosemary, garlic, and black pepper. Roasting at high temperature creates a crisp exterior similar to fries, without the deep-fry oil absorption.
- Boiled Baby Potatoes with Herbs Boil baby potatoes whole until fork-tender, then toss with fresh dill, parsley, and a small amount of olive oil. Simple, fast, and directly aligned with the “boiled” preparation category the study found had no significant diabetes risk increase.
- Olive Oil Mashed Potatoes Swap butter and cream for olive oil and a splash of low-sodium vegetable broth when mashing. This keeps the comforting texture of traditional mashed potatoes while improving the fat profile.
- Potato and Vegetable Soup Combine boiled potatoes with leeks, carrots, and white beans for a fiber-rich soup that pairs starch with protein and fiber, helping moderate the overall blood sugar response of the meal.
- Loaded Baked Potato with Greek Yogurt Bake a potato until tender, then top with Greek yogurt instead of sour cream, plus chives, a small amount of cheese, and steamed broccoli. This adds protein and fiber directly to the dish, addressing one of the key strategies for reducing the glycemic impact of starchy foods.
Frequently Asked Questions
Are baked potatoes safe for diabetics?
Yes. The Harvard study of over 205,000 people found that baked, boiled, and mashed potatoes were not associated with a significant increase in type 2 diabetes risk. This held true even though the broader “total potato” category showed a modest 5% increased risk per three weekly servings, a number driven largely by french fries within that category. People managing diabetes can include baked or boiled potatoes in a balanced diet, ideally paired with fiber and protein.
How many servings of french fries are safe?
The study found that three weekly servings of french fries were associated with a 20% higher risk of type 2 diabetes. The lead researcher noted that even less than one weekly serving showed an association with increased risk. No safe threshold was identified in the data, so the most practical guidance is to treat french fries as an occasional food rather than a weekly habit.
Is white rice worse than potatoes for diabetes?
According to the study’s substitution analysis, replacing potatoes, including baked, boiled, or mashed varieties, with white rice was associated with a higher type 2 diabetes risk, not a lower one. This challenges the common assumption that white rice is a neutral or healthier carbohydrate option. Whole grains, not white rice, were identified as the better substitution for lowering diabetes risk.
What are the best carbs for preventing diabetes?
The study found that whole grains such as whole grain bread, pasta, farro, quinoa, and brown rice were the most effective substitution for lowering type 2 diabetes risk. Replacing three weekly servings of french fries with whole grains was estimated to lower diabetes rates by 19%, while replacing baked, boiled, or mashed potatoes with whole grains lowered risk by 4%. Whole grains’ higher fiber content slows glucose absorption and supports better insulin sensitivity compared to refined starches.
Why do french fries increase diabetes risk more than other potatoes?
French fries are deep-fried in oils that typically contain trans or saturated fats. The body’s metabolism of these fats can contribute to insulin resistance, where cells stop responding properly to insulin. Frequent fried food consumption is also linked to obesity and chronic inflammation, both of which independently raise diabetes risk. Baked, boiled, and mashed potatoes skip the frying process entirely, which appears to explain why they did not carry the same risk in this study.
The Bottom Line
The Harvard T.H. Chan School of Public Health study, published in The BMJ and built on nearly 40 years of data from over 205,000 people, delivers a finding that is both reassuring and actionable: potatoes are not the problem. French fries are.
Eating three weekly servings of french fries was linked to a 20% higher risk of type 2 diabetes. Baked, boiled, and mashed potatoes carried no significant increase in risk. Swapping fries, or any potato preparation, for whole grains was linked to meaningfully lower diabetes risk, while swapping for white rice made things worse, not better.
As Dr. Mousavi put it, the question is no longer “are potatoes good or bad?” It is “how are they prepared, and what might we eat instead?”
For the millions of people managing or trying to prevent type 2 diabetes, this study offers something rare in nutrition science: clear, practical, and genuinely good news. You do not have to give up potatoes. You just have to put down the fryer.
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