Potatoes are a perpetually controversial food. They can be part of healthy, whole-foods diet (such as vegetarian, Paleo, or Mediterranean), but they also have a dark side. When researchers from Harvard’s School of Public Health sought to answer the age old question, “Are potatoes healthy?” they found that potatoes—especially French fries–can increase the risk of becoming diabetic.[1]

Study found 7% to 33% higher diabetes risk

The study combined data from nearly 200,000 adult men and women, none of whom had diabetes at the start of the study. Researchers assessed the number of servings of baked, boiled, mashed, or French fried potatoes eaten per week based on scientifically validated food frequency questionnaires.

The results showed that people who ate more potatoes had a significantly higher risk of type 2 diabetes. Compared to people who ate less than one serving per week, those who ate seven or more servings per week had 33% increased risk, while those who ate less than two to four servings of potatoes per week had a 7% increased risk of type 2 diabetes.

People who ate French fries had a higher risk of type 2 diabetes than those who ate baked, boiled, or mashed potatoes. For every three servings of French fries eaten per week, the risk of type 2 diabetes increased by 19%.

Could some other factor, like weight gain, be responsible for the increased risk?

As study was observational, it cannot not prove that eating too many potatoes causes diabetes. Could some other factor be responsible for the correlation? The researchers tried to take into account individual dietary factors, changes in body weight (BMI) over time, and the effect on blood sugar (glycemic load) from all foods except potatoes (to account for the quality and quantity of total carbohydrate). Even when statistically adjusting the data to account for these factors, the results did not change.

This makes it more likely that the consumption of potatoes themselves and not some other factor (like total carbohydrates in the diet or weight gain) is responsible for the association between eating potatoes and diabetes risk. However, even though the researchers tried to control many factors, they could not control for everything. As you’ll see below, it may be that if potatoes are eaten in the context of a healthy diet and lifestyle, they are not correlated with diabetes risk.

Dietary guidelines for potatoes

Potatoes should be considered “refined grains, rather than vegetables,” stressed Isao Muraki, MD, PhD, the lead author of the study, which was published in Diabetes Care.[2] “Potato food consumption should be reduced for people with elevated risk of developing diabetes or insulin resistance.”

To prevent diabetes, he says that people should focus on “healthy foods such as vegetables, fruits, whole grains, and nuts, rather than potatoes.” The researchers estimated that if three servings per week of potatoes (regardless of type) are replaced with whole grains, the risk of type 2 diabetes would decrease by 12%.

Are potatoes healthy in some circumstances?

Not everyone who eats potatoes has an elevated risk, according to another study, published in the European Journal of Clinical Nutrition.[3] When eaten as part of a whole foods-based diet potatoes have a neutral effect on diabetes and may even decrease the risk.[3] A whole foods-based diet is one dominated by foods that are unprocessed and unrefined, or processed and refined as little as possible.

If you’re not at high risk for diabetes and eat a whole-foods diet, potatoes can be a healthy part of your diet. Choose sweet potatoes and purple potatoes to get more phytonutrients than white potatoes. Purple potatoes have particularly high antioxidant activity and phytonutrient content. The purple color comes from the anthocyanins, phytonutrients that act as antioxidants and anti-inflammatories. Purple potatoes have been shown to protect against colon cancer and given their high anthocyanin content, they likely help protect against many other age-related chronic diseases, too.[4]

Cooking methods have been shown in studies to make big differences on the nutritional properties of vegetables, and potatoes are no exception. A study comparing different cooking methods for purple potatoes, for example, found that compared to stir frying, baking, boiling, and frying, steaming and microwaving were the only methods in which the potatoes retained most of the health-promoting compounds found in raw potatoes.[5]

Acrylamide is a neurotoxin and likely carcinogen produced when potatoes and other starchy foods are cooked at high heat, especially frying. French fries, potato chips, and hashbrowns have been found to be major dietary contributors of acrylamide.[6] Whether acrylamide had anything to do with the particularly strong association found between French fry consumption and type 2 diabetes in the study discussed above is unknown. The acrylamide research does suggest, however, that eating too many fried potatoes of any kind is probably not the wisest choice for overall health and longevity.

It’s also a good idea to eat your potatoes cold. The cooling process changes the easily digested starch in hot potatoes into resistant starch, which has less impact on blood sugar.[7]

Tell us about your potato consumption

Are potatoes healthy in your opinion? Do you include them in your diet? Share your experience in the comments section, below.

[1] Diabetes Care. 2015 Dec 17. [Epub ahead of print]

[2] Medscape Medical News. Potatoes Tied to Higher Risk of Type 2 Diabetes; French Fries Worst. Dec 24, 2015.

[3] Eur J Clin Nutr. 2015 Aug;69(8):944-8.

[4] J Nutr Biochem. 2015 Dec;26(12):1641-9.

[5] Food Chem. 2016 Apr 15;197 Pt B:1264-70.

[6] Plant Foods Hum Nutr. 2011 Nov; 66(4): 307–312.

[7] Adv Nutr. 2013 May; 4(3): 393S–401S.

Originally published in January 2016 and updated.