French Fries and Diabetes: Why Fried Potatoes Raise Risk, But Baked and Boiled Potatoes Don't

In a world where type 2 diabetes (T2D) is becoming increasingly common, understanding the impact of daily diet on the risk of developing it is especially important. A new study from the Harvard T. H. Chan School of Public Health sheds light on the role of potatoes, one of the most popular carbohydrate sources in the diets of millions of people.

What was researched and how?

The researchers pooled data from three large longitudinal cohort studies in the United States: the Nurses' Health Study, the Nurses' Health Study II, and the Health Professionals Follow-up Study. A total of 205,107 people participated in the analysis, who responded to detailed questionnaires every 2-4 years for 30-36 years:

• Frequency of consumption of staple foods, including French fries, baked, boiled, and mashed potatoes, and various whole grain products (bread, pasta, cereals such as farro).
• New diagnoses, particularly type 2 diabetes, as well as changes in weight, physical activity, smoking, medication use, and other lifestyle factors.

Over the entire follow-up period, 22,299 participants reported the development of T2DM. Statisticians adjusted the data for age, body mass index, total energy intake, and other variables to assess the independent effects of different forms of potatoes on disease risk.

Main results

1. French Fries and Type 2 Diabetes Risk

   • Three servings of French fries per week (approximately 150–180 g raw tubers before cooking) were associated with a 20% increased risk of T2DM.

   • This is most likely due to the high fat content and glycemic load (rapid rise in glucose and insulin levels), as well as the formation of fat oxidation products during deep frying.

2. Baked, boiled and mashed potatoes

   • Eating three such servings per week did not statistically significantly affect the risk of T2DM. That is, the structure of the starchy product itself, without excessive fat and extreme cooking temperatures, does not contribute to the development of the disease.

3. Benefits of Whole Grain Products

   • Replacing three servings of potatoes (any form) per week with whole grain pasta, bread or cereal reduced the risk of T2D by 4%.

   • If we were talking specifically about replacing French fries, the reduction reached 19%.

4. Additional meta-analysis

   • The authors conducted two large meta-analyses: one using data from 13 cohorts on potato consumption (over 400,000 participants), and the second using data from 11 cohorts on whole grains (over 500,000 participants).

   • Their results confirmed that each increase in French fry consumption by three servings per week resulted in an approximately +16% increase in the risk of T2D, while replacing it with whole grains reduced the risk by 7–17%.

Why French Fries Are "More Dangerous"

1. High glycemic load (GL).
   Fried potatoes are quickly digested, causing a sharp jump in blood glucose and insulin levels. Chronic “glycemic peaks” lead to insulin resistance, the main pathogenetic link in type 2 diabetes.

2. Starch transformations.
   When fried, some of the starch is converted into easily digestible dextrins, further accelerating the absorption of carbohydrates.

3. Fats and oxidation products.
   Deep-frying oil contains saturated and trans fats, and high temperatures promote the formation of toxic oxidation products (acrolein, aldehydes), which negatively affect metabolism.

4. Low fiber content.
   Unlike whole grains, French fries contain virtually no dietary fiber, which slows down digestion and improves tissue sensitivity to insulin.

Practical advice

1. Reduce the proportion of French fries.
   Make French fries a "rare guest" on the table: no more than once every two to three weeks.

2. Prepare alternative dishes.
   Bake potato wedges with a minimum amount of oil or steam mash them - this way vitamins are preserved and the glycemic load remains moderate.

3. Add whole grains.
   Replace some of your regular potatoes (especially French fries) with whole-grain pasta, brown rice, quinoa, or farro. This will help add variety to your diet and reduce your risk.

4. Control your portions.
   Try not to exceed the serving size of starchy foods (potatoes, rice, pasta) more than 150 g in cooked form at one time.

5. Include fiber.
   Add vegetables, legumes, and whole grain salads to your main dishes — this will improve digestion and slow down the absorption of carbohydrates.

Summary

This study highlights the importance of not only what we eat, but also how we cook it and what we can replace unhealthy foods with. Potatoes themselves are not a “health enemy,” but their culinary transformation (especially in deep frying) can increase the risk of chronic metabolic disorders. Small but conscious changes in diet can be an effective strategy for preventing type 2 diabetes at both the individual and societal level.