Restaurants have changed cooking fats many times since the old announcement that appeared on this page. The lasting lesson is how to choose everyday foods made with better ingredients. Industrial trans fats were widely used in partially hydrogenated oils because they were convenient for frying and shelf life. They are not a health-promoting part of a natural-food diet.
What did controlled feeding studies find?
In a randomized crossover feeding study, 29 adults ate carefully controlled diets that differed in fat composition. Replacing saturated fats with trans fats lowered HDL cholesterol and impaired a measure of artery response called flow-mediated dilation (controlled trans-fat feeding trial). These are cardiovascular risk markers, not a direct count of heart attacks, but the controlled comparison helps show that the fat itself can alter physiology.
A later double-blind crossover trial in 106 adults compared fats including those from partially hydrogenated oil and measured blood lipids (randomized dietary-fat comparison). Such trials helped inform policy. The FDA concluded that partially hydrogenated oils, the main industrial source of trans fat, were no longer generally recognized as safe for food use (FDA final determination).
A practical food-first choice
Choosing minimally processed meals, fruit, vegetables, nuts, and oils such as olive oil is more useful than relying on a restaurant's old marketing promise. Ingredient lists can reveal partially hydrogenated oils, while a zero on a nutrition label may still require context about serving size. The goal is not to fear every naturally occurring trace of trans fat, but to avoid making industrially hydrogenated fat a routine ingredient.
