Fully vs. Partially Hydrogenated Oils: Is One Fat Healthier than the Other?

(Originally published Dec. 3, 2008 – Suite101.com)

author cohdra, morguefile.com 2004

Savvy consumers are familiar with the fact that trans fats are found in hydrogenated oils, but there are serious differences in the associated terminology.

Quite often, the words “hydrogenated” and “partially hydrogenated” are used interchangeably in the processed food industry. Both refer to a process whereby a liquid vegetable oil is made into a solid or semi-solid fat (known as a shortening) for use in margarine, peanut butter, baked goods, and similar products. The use of such oils promotes a longer shelf life and a more consistent texture. It’s also cheaper than animal fat alternatives such as butter or lard.

Confusion sets in, however, when the words “hydrogenated” and “fully hydrogenated” are also used interchangeably. While the processing of fully and partially hydrogenated oils is basically the same, the end products are very different – especially in how they relate to your health.


The process of hydrogenation changes an unsaturated liquid vegetable oil into a solid or semi-solid fat by exposing it to a hydrogen gas and a catalyst under varying degrees of heat and pressure. Depending on the duration of exposure, the resulting oil will become more or less saturated, and thereby more or less solid at room temperature.

A partially hydrogenated oil is semi-solid. Being partially hydrogenated means it’s also only partially saturated. The remaining unsaturated oils are chemically converted to health-damaging trans fats.

A fully hydrogenated oil, on the other hand, is a more solid, waxy substance that’s harder to work with. Such fats are often blended with other oils to make them easier to mix into various processed foods. However, the most important characteristic of a fully hydrogenated oil is that it is fully saturated and thus contains virtually no trans fat.


While the health dangers of trans fats from partially hydrogenated oils have been widely documented in both the media and scientific journals, fully hydrogenated oils have yet to be seriously examined for possible health implications.

One obscure study published in The Journal of Nutrition in May 1998 found that fully hydrogenated oil was poorly digested in rats and mostly excreted. Unfortunately, the study didn’t examine health effects that may have resulted from whatever amounts of the oil were digested.

To date, the primary focus of attention has been on the fact that fully hydrogenated oils contain virtually no trans fats. Being fully saturated, they are typically regarded as no different than any other saturated fat in terms of their effects on your health.

One flaw in this view, however, is that healthy dietary oils only remain healthy so long as they aren’t exposed to heat or light. Once so exposed, they oxidize and turn rancid – a process which creates free radicals. And as you might have heard, free radicals are nasty little buggers that have been implicated in everything from aging to cancer…and so should be absolutely avoided.

The process of hydrogenation, by definition, chemically converts unsaturated oils using extremes of heat and pressure to work its magic. Intuitively, this at least suggests that the end product is not as healthy as the starting product.

As an example, hydrogenation is typically performed on polyunsaturated oils. These oils in particular are so fragile that they can begin to oxidize even at room temperature and in low-light conditions. One can thus only imagine the havoc wrought on the oil during hydrogenation.

When considering all the above, those consumers watching out for their health would be wise to shun any product with any variation of the terms “hydrogenated” or “shortening” in the ingredients list – regardless of how the food industry uses them.



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