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"Hydrogenated oils" (or fats), and especially "partly hydrogenated oils" are quite commonly among ingredients on the food store item's product label. It suggests that many people still don't pay attention to food ingredients, or don't know how unhealthy these fats can be. Here's in little more details what they are, and how do they affect your health.

The term "hydrogenation" refers to a process of transforming unsaturated fats into saturated by adding to their molecules more hydrogen atoms. This makes oil stable, and unhealthy; it destroys most nutrients, while creating some trans-fatty acids and other altered (unhealthy) fat molecules. 

Fats are often "partially hydrogenated", which means that the process of hydrogenation is deliberately stopped at some point before completion, in order to achieve certain level of oil/fat consistency. This is how margarines, shortenings and partially hydrogenated vegetable oils are made.

Don't think - as I used to - that "partially hydrogenated" is less bad than "hydrogenated". It is exactly the opposite. While most of fully hydrogenated fats is in a relatively harmless saturated form, partially hydrogenated fats have significantly higher proportion of toxic, twisted fatty acids in transition from unsaturated to saturated form (hence "trans-fatty"). While most of them are formally still either polyunsaturated, or even super-unsaturated, their structure has changed, making them unhealthy for the body.

The worst of commercial bad fats is probably margarine. It can contain in excess of 60% trans-fatty acids. This, however, doesn't prevent many doctors from recommending it to their patients suffering from cardiovascular disease.

While the rationale for it is that margarine does not contain cholesterol, this long-established medical practice (in the US, not in Europe anymore) is, at the present level of scientific knowledge, inexcusable. Trans-fatty acids do increase total cholesterol and decrease HDL ("good") cholesterol, while interfering with liver function and joining free radicals in causing damage at the cellular level. Beside, it is well documented for some time that cholesterol itself is not a main risk factor for developing cardiovascular disease.

Another health risk of hydrogenated fats, either fully or partially, is that they are often contaminated with metal catalysts used for hydrogenation, nickel and aluminum, as well as other chemical contaminants used during their processing and refining.