What are trans fatty acids, and where do they come from?
We're used to hearing about saturated and unsaturated fatty acids. Saturated fatty acids - which come from animal fats (meat, lard, dairy products) as well as tropical oils such as coconut and palm oils - raise the levels of LDL cholesterol. Unsaturated fats - which come from vegetable oils - in general, do not increase cholesterol levels, and may reduce them. Because saturated fatty acids were found to be bad for you a couple decades ago, the food industry wanted to switch to using unsaturated fatty acids. Unfortunately, unsaturated fatty acids become rancid relatively quickly. To combat the instability of unsaturated fatty acids, manufacturers began to "hydrogenate" them, a process that makes them more stable. The result was a more solid and longer lasting form of vegetable oil, called "partially hydrogenated" oil. Unfortunately, when unsaturated vegetable fats are subjected to the process of hydrogenation, a new type of fatty acid is formed. This new type of fatty acid is called trans fatty acid. So when manufacturers began substituting partially hydrogenated vegetable oils for saturated fats in processed foods, they began adding - for the first time - relatively large amounts of trans fatty acids to the typical diet. So what's the problem with trans fatty acids?
Trans fatty acids turn out to increase total cholesterol levels and LDL cholesterol levels, and to reduce HDL cholesterol levels. In other words, trans fatty acids are detrimental to cardiac health. Which is worse - saturated fatty acids or trans unsaturated fatty acids? Both saturated fats and trans fatty acids are bad for you. Saturated fats are almost always found in foods that also contain cholesterol, so saturated fats offer a "one-two" punch to heart health. On the other hand, trans fatty acids not only increase LDL cholesterol, they also decrease HDL cholesterol. So while nobody can say yet definitively which is worse, it does appear...
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