Life-changing habits often begin with small choices—such as how we prepare our everyday foods. A recent study at August 2025 from Harvard T.H. Chan School of Public Health brings new clarity: not all potatoes are created equal, especially when it comes to the risk of type 2 diabetes. The key question isn’t simply whether potatoes are “good” or “bad,” but how we cook them—and what we choose to eat instead1.
Deep Dive into the Harvard Study
This research is one of the largest and longest studies of its kind, drawing on over 205,000 adults from three major U.S. health studies:
- Nurses’ Health Study (NHS) – Began in 1976, following registered nurses across decades.
- Nurses’ Health Study II (NHS II) – Started in 1989, with younger nurses.
- Health Professionals Follow-up Study (HPFS) – Since 1986, tracking male health professionals.
Participants were free of diabetes, cancer, and cardiovascular disease at the start. They were followed for up to 36 years, with food intake recorded every 4 years using detailed food-frequency questionnaires.
Researchers specifically examined total potato intake and broke it down by preparation method:
- French fries – deep-fried potatoes, often with added salt and oils.
- Baked, boiled, or mashed potatoes – non-fried preparations.
- Other potato-based dishes (like potato salad) were noted but not the main focus.
Over the study period, over 15,000 new cases of type 2 diabetes were diagnosed among participants.
Key Findings of the Study
- French fries raise diabetes risk
- People who ate three or more servings of French fries per week had a 20% higher risk of developing type 2 diabetes compared to those who ate less than one serving per week.
- This effect remained even after adjusting for body weight, age, activity level, smoking, and other dietary factors.
- Baked, boiled, or mashed potatoes are neutral—but still starchy
- No clear increased risk was found for these forms when eaten in moderate amounts.
- However, replacing them with whole grains still brought a modest reduction in risk.
- Food swaps make a difference
- Replacing one serving per day of total potatoes with whole grains reduced type 2 diabetes risk by 4%.
- Replacing one serving of French fries with whole grains reduced risk by 19%—a much bigger drop.
- The carbohydrate quality matters
- Potatoes—especially fried ones—are high-GI foods that can cause rapid spikes in blood sugar and insulin.
- Over time, these spikes contribute to insulin resistance, which is a direct pathway to type 2 diabetes.
Why French Fries Are the Worst Offender
French fries combine three diabetes-promoting factors:
- High Glycemic Load – The starch in potatoes turns quickly into glucose, spiking blood sugar.
- Frying Damage – High-heat frying produces compounds like acrylamide and oxidized fats, which are harmful to metabolic health.
- Calorie Density – Frying soaks potatoes in oil, making them calorie-heavy and easy to overeat.
How Cooking Methods Affect the Glycemic Index (GI)
- Fried potatoes (French fries): High GI plus added fats; faster starch breakdown; harmful oil byproducts.
- Boiled potatoes: Moderate-to-high GI; less calorie-dense; GI can be lowered if cooled before eating.
- Mashed potatoes: GI can be high due to the smooth texture, which speeds digestion.
- Baked potatoes: Often high GI when hot; cooling increases “resistant starch,” which digests slower and may help blood sugar control.
Bottom line: The way potatoes are prepared changes how they affect your blood sugar—and therefore your long-term diabetes risk.
Why a Low-Carb Diet Strengthens the Findings
The Harvard data fits perfectly with the low-carb approach:
- Reduce high-GI carbs (like fries, white bread, sugary drinks).
- Replace with nutrient-dense, fiber-rich foods like vegetables, nuts, seeds, and moderate whole grains.
- Stabilize blood sugar, improve insulin sensitivity, and help maintain healthy weight.
In other words: low-carb eating doesn’t mean “no carbs”—it means “better carbs.”
My Take as a Low-Carb Advocate
From my perspective, this research is another clear sign that carb quality matters more than carb quantity alone. You can eat the same vegetable—potato—but the way you prepare it can turn it into either a harmless side dish or a blood-sugar bomb.
Here’s what I see in daily practice:
- People who replace French fries with low-carb vegetables—like roasted cauliflower, zucchini fries, or avocado—almost always report more stable energy and fewer cravings.
- Those who keep potatoes but eat them in smaller portions, paired with protein and healthy fats, often find their blood sugar easier to control.
- Cooling potatoes before eating is a small trick that can make a big difference—something most people don’t know.
The Harvard study’s findings are not anti-potato—they’re anti-blood sugar spikes. And the low-carb lifestyle is all about minimizing those spikes while maximizing nutrient density.
If you’re looking for a practical takeaway, it’s this: swap more, spike less. Replace high-GI carbs with nutrient-dense alternatives, and you’ll likely improve not only your blood sugar but also your weight, energy, and long-term health.
How to Apply These Findings at Home
- Limit French fries to an occasional treat.
- If eating potatoes, boil, bake, or mash—and try cooling before eating to lower GI.
- Replace at least one potato serving per day with whole grains, legumes, or non-starchy vegetables.
- Pair carbs with protein or healthy fats to slow blood sugar spikes.
- Focus on overall carb quality, not just the type of food.
Final Thoughts
The Harvard study shows that potatoes are not an all-or-nothing food—but preparation and portion control matter. French fries clearly raise diabetes risk, while other potato forms are safer but still best eaten in moderation. Choosing low-GI, whole-food carbs—or going lower-carb overall—gives your body the best chance at long-term health.
It’s not about “never eat potatoes again”—it’s about making swaps that protect your future health.
- Harvard T.H. Chan School of Public Health. Potatoes may increase risk of type 2 diabetes depending on their preparation. Published June 26, 2024. https://hsph.harvard.edu/news/potatoes-may-increase-risk-of-type-2-diabetes-depending-on-their-preparation ↩
