French fries, but not mashed potatoes, linked to type 2 diabetes
1 of 2 | Consumption of french fries, but not potatoes prepared in other ways, was linked to increased levels of type 2 diabetes in a Harvard study released Wednesday. File photo by Bill Greenblatt/UPI | License Photo
French fries, but not mashed, baked or boiled potatoes, were linked Wednesday to type 2 diabetes in a study whose authors say food preparation, as well as the kinds of foods eaten, makes a difference in reducing health risks.
Researchers at Harvard University’s T.H. Chan School of Public Health also found that by swapping out French fries with whole grains, a person can reduce the risk for type 2 diabetes by 19%.
The new paper, led by postdoctoral researcher Seyed Mohammad Mousavi and co-authored by prominent Harvard nutrition and epidemiology expert Walter Willett, was published in The British Medical Journal.
After examining data about the diets and diabetes outcomes of more than 205,000 adults enrolled in a trio of major longitudinal U.S. studies spanning more than three decades, they determined that three servings weekly of french fries was associated with a 20% excess risk of developing type 2 diabetes, or T2D.
Conversely, they saw no significant association between consumption of baked, boiled or mashed potatoes and risk of T2D, despite potatoes being “highly stigmatized” and dismissed as generally unhealthy by some in the nutrition world.
The results led the authors to conclude that how foods are prepared matters just as much as what types of foods are eaten in the risk for diabetes, which last year affected 38.4 million Americans of all ages, some 11.6% of the population. The vast majority of cases are type 2 diabetes, which is highly associated with obesity and poor diet.
“For consumers, the takeaway is simple: how you prepare a food can be just as important as what you eat,” Mousavi told UPI in emailed comments. “A boiled or baked potato has a very different impact on health than the same potato deep-fried at high temperatures in unhealthy oils.”
He said he and his colleagues hope the results will help shift the conversation about healthy diets to into more “nuanced — and useful” directions and away from blanket condemnations of certain foods, which usually are not “‘good’ or ‘bad’ in isolation — it’s always good or bad compared to what.
“If you swap potatoes, especially fries, for whole grains, you gain health benefits; if you swap fries for another fried snack, you probably won’t. Choosing cooking methods that minimize added fats, salt, and harmful compounds, and making thoughtful replacements, is key,” Mousav said
Deep frying is one of the unhealthiest ways to cook, according to the American Diabetes Association, which notes that frying creates trans fats that have been shown to cause heart disease and stroke. Often, frying requires the use of flour or breading, which also adds carbohydrates.
The current study used a new kind of “meta-analytic” approach to estimate how swapping potatoes for whole grains could affect the risk of T2D. It involves 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 involving more than 500,000 participants, including 43,000 with a T2D diagnoses, from across four continents.
While french-fried potatoes and other types of deep-fried foods have long been suspected as a risk factor for T2D, the new study has deepened understanding of the link on several levels, such as by showing the risk is “dose-dependent” and begins at relatively low intakes — even less than one serving of fries per week, Mousavi said.
“Second, we confirm that not all potato preparations carry the same risk, highlighting that deep-frying is the key driver here,” he added. “Third, we compared the effect of fries with other carbohydrate sources and found that, except for white rice, all other carb sources were healthier choices than fries.
“By combining decades of detailed dietary data with a meta-analysis across multiple populations, we provide stronger evidence that it’s not just the food itself, but also the frying process — and what you choose to replace it with — that matters for diabetes risk.”
Some other researchers have suggested that potatoes have gotten a bad rap when automatically lumped in with foods that are considered a risk for diabetes.
Dr. Hana Kahleova, director of clinical research for the Physicians Committee For Responsible Medicine, a Washington-based nonprofit group that advocates for healthier foods, agreed it’s wrong to dismiss potatoes as unhealthy without regard for how they’re prepared.
Rather, some studies “suggest that potatoes, particularly boiled potatoes, may have beneficial effects on body weight and reduce the risk of diabetes,” she told UPI.
“Potatoes can be consumed in many ways,” Kahleova said. “The data from the National Health and Nutrition Examination Survey show that french fries are the most consumed vegetable in the U.S. When Americans eat away from home, french fries make up almost two-thirds of all consumed potatoes.
“At home, most potatoes are consumed as potato chips. The cooking method and the foods people consume potatoes with seem to be responsible for the bad rap of potatoes.”
Some research shows that potatoes can reduce the risk of diabetes and lead to weight loss, including a 2022 study on behalf of the Alliance for Potato Research and Education that found consuming baked white potatoes produced no harmful effects on measured health outcomes and actually provided some cardiometabolic health benefits when substituted for foods such as long-grain white rice.
Similarly, Kahleova cited Finnish and Dutch cohort studies that span a 20-year follow-up period that reported a lower risk of T2D was associated with increased consumption of potatoes, along with an increase in vegetables and legumes.
“In a cohort study conducted in almost 2,000 adults in Iran who were followed for six years, the risk for incident diabetes was 54% lower in people with higher intakes of total potatoes, and 53% lower for high intake of boiled potatoes, compared with those who had the lowest intakes,” she said.
The latest french-fry findings “contribute to the totality of the evidence on eating patterns and their association with health risk,” concurred dietician Stacey Krawczyk, director of nutrition and wellness for the American Diabetes Association.
“Eating patterns that have several weekly servings of fried foods, potatoes in this case, may also have other lifestyle and meal choices that could also contribute to a person’s overall health,” she told UPI.
“We encourage people to choose a variety of foods when building ADA’s Diabetes Plate,” in which potatoes earn a spot on the dish as a “quality carbohydrate” along with starchy vegetables, legumes, whole grains, fruits, milk and yogurt.
“We encourage people to use a foundation of whole and less-processed forms of foods as they build their balanced plate,” Krawczyk added. “In general, using methods of cooking that do not involve frying are preferred.”
Study co-author Mousavi said his study underscores the need to “move beyond” the broad food categories now found in typical nutrition guidelines.
“Lumping all potatoes — or all grains, for that matter — into a single group can hide important differences in health effects,” he said.
“Policy recommendations and public health messaging should highlight not just the food itself, but also its preparation and what it’s replacing, as these factors can dramatically change its nutritional quality and long-term health impact.”