What is hydrogenated vegetable oil, and why is it bad?

Fat deposits above the fast food fryer (photo by John Lewis - CC-BY)

Fat deposits above the fast food fryer (photo by John Lewis - CC-BY)

Hydrogenated vegetable oil is a manufactured product produced by taking a normal vegetable oil and adding metal as a catalyst. The mixture is heated and hydrogen is forced through it. The hydrogen attaches to the unsaturated vegetable oil. If there’s enough hydrogen, you end up with saturated fat. But if the hydrogen is restricted, you end up with partially hydrogenated vegetable oil (after you remove the catalyst).

In this article, when we talk about hydrogenated vegetable oil we mean this partially hydrogenated vegetable oil.

The food technologists love this hydrogenated oil. It has a nice feel in the mouth, it’s not too runny and not too solid, it doesn’t have much taste, and it keeps very well. And it’s cheap! It can be used to bake biscuits and cakes that don’t go off quickly, or as the main ingredient to manufacture margarine.

When hydrogenation was discovered in the early 1900s and applied to food oils a few years later, it was assumed that the partially saturated end product would be healthier than saturated fats, but this couldn’t have been more wrong.

It turns out that our bodies can’t deal properly with hydrogenated vegetable oil. The hydrogenation changes the shape of the fat molecule (from a cis fat into a trans fat) which our bodies cannot recognise and do not deal with properly. Trans fat provides no known nutritional benefit, and is implicated in heart disease and diabetes. The National Academy of Sciences has concluded that there is no safe level of trans fat consumption.

A 2006 study published in the New England Journal of Medicine estimated that between thirty and a hundred thousand cardiac deaths each year are attributable to the consumption of trans fats. An earlier review in the same journal found that replacing 2% of energy intake from trans fatty acids with cis fatty acids was associated with a 53% decrease in the risk of coronary heart disease. These are huge numbers for a single dietary factor.

The major sources of hydrogentated vegetable oil in the western diet are margarines, commercial baked goods, and fast foods fried in hydrogenated vegetable oil.

Look out for “hydrogenated vegetable oil” on food ingredient labels. It’s also known as vegetable shortening.

And try tasting a biscuit made with butter. You’ll realise that it tastes much better than the one made with hydrogenated vegetable oil.

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