Led by Leah Cahill, research fellow in the Department of Nutrition at Harvard School of Public Health (HSPH), and An Pan of the National University of Singapore’s Saw Swee Hock School of Public Health, the researchers examined data from more than 100,000 men and women over 25 years. They found that people who ate fried food at least once per week had a greater risk of both type 2 diabetes and heart disease, and that the risk increased as the frequency of fried food consumption increased. For instance, participants who ate fried foods 4-6 times per week had a 39% increased risk of type 2 diabetes, and those who ate fried foods 7 or more times per week had a 55% increased risk, compared with those who ate fried foods less than once per week.
Eating fried foods away from home—where frying oil may not be fresh—posed the greatest risk, Cahill said. With each reuse, oil becomes more degraded, and more gets absorbed into food, which can contribute to weight gain, higher cholesterol, and higher blood pressure—all risk factors for type 2 diabetes and heart disease.