What it is
Partially hydrogenating a liquid oil makes it more solid. It also makes trans fat. In WHO’s words, “trans fat is produced industrially by the partial hydrogenation of any liquid oils.”1
What WHO says
WHO calls for industrially produced trans fat to be eliminated, and notes it “can be eliminated and replaced with healthier fats or oils.” For adults, it recommends keeping trans fat to “less than 1% of total energy intake, which is less than 2.2 g per day for a 2000-calorie diet.”1
It’s direct about why: high intake of trans fat “increases the risk of death from any cause by 34%, coronary heart disease deaths by 28%, and coronary heart disease by 21%.”1
What the US decided
In 2015 the FDA determined that partially hydrogenated oils are no longer “generally recognized as safe (GRAS) for any use in human food.” In 2023 it revoked the last remaining authorizations, for uses in margarine, shortening and bread, concluding that “these uses of PHOs may be injurious to health.” That took effect on December 22, 2023.2
Fully hydrogenated is a different ingredient
The US decisions are about partially hydrogenated oils. Fully hydrogenated oil is a separate ingredient, and isn’t what they cover. So read the word before “hydrogenated” carefully.