Despite unsaturated oil’s origin, once you’ve zapped it with high-pressure hydrogen, heated it or treated it with chemical solvents it turns into a saturated fat and behaves that way in the body. This hydrogenation process is how vegetable oil is turned into margarine. Hydrogenated fats contain another kind of fat that falls outside the saturated and unsaturated categories. It’s called “trans fatty acids”. It’s basically a molecule that has its head on backwards. For your arteries, trans fats are as bad as (or worse) than saturated fats. Many studies have shown that trans fats raise cholesterol levels in the blood. Even if a label says it’s low in heart damaging saturated fat, it may still contain a large amount of trans fats. Trans fats raise the level of LDL (bad) cholesterol, while reducing the level of HDL (good) cholesterol. Trans fats have been shown to decrease the body’s ability to produce natural substances that regulate many of the body’s functions. Trans fats and hydrogenated fats may interfere with the ability of the cells of the body to metabolize the fats that are good for you. This may damage cell membranes of vital structures, such as the brain and nerve cells.
Hydrogenated fats are also widely used in restaurants for deep-fat frying, so the French fries so popular with children may be full of cholesterol-raising trans fats even if the establishment claims it uses “100% vegetable oil” for cooking.
Current label laws in the US do not require food manufacturers to include information about trans fats in nutrition labeling.