Research published in the American Journal of Clinical Nutrition (June 2001;73:1001–1002, 1019–1026) found that trans fats—commonly found in packaged and processed foods—significantly increase the risk of developing type 2 diabetes. Trans fats are present in many cookies, crackers, baked goods, margarines, and some salad dressings, and are typically identified on food labels as “hydrogenated oil” or “partially hydrogenated oil.” Fortunately, these have been banned by the FDA (see below).
The researchers followed 84,204 women aged 34–59 who were free of diabetes, cardiovascular disease, and cancer at baseline in 1980. Detailed dietary intake was assessed using validated food-frequency questionnaires and updated repeatedly in 1984, 1986, and 1990.
The findings were striking. A mere 2% increase in daily calories from trans fats was associated with a 39% increase in the risk of developing type 2 diabetes. In contrast, replacing calories with polyunsaturated fats was protective—a 5% increase in calories from polyunsaturated fats was associated with a 37% reduction in diabetes risk.
These findings highlight the metabolic danger of trans fats and support dietary patterns that emphasize healthier fats, not just lower fat intake overall. The type of fat consumed plays a critical role in insulin sensitivity and long-term metabolic health.
Update: Since this study was published, industrial trans fats have been largely banned from packaged foods in the United States due to their health risks. However, the findings remain important in illustrating how fat quality—not just calorie intake—can strongly influence insulin resistance and diabetes risk.
