We all know trans-fats are bad, and if you’ve been following this blog, you also know that if partially hydrogenated oil appears in a product ingredient list, that means it contains trans-fats.
But what about FULLY hydrogenated oils?
What you need to know:
To understand this hydrogenation stuff, let’s familiarize ourselves with oils and fat. We promise to make this as simple as possible.
Fat is solid at room temperature; Oil is liquid, but some oils are semisolid at room temperature. All oils and fats are composed of fatty acids. Fatty acids are molecules with lots of carbon, oxygen, and hydrogen atoms. They are classified into 2 main types -
- saturated fatty acids
- unsaturated fatty acids
The two types of fatty acids are quite similar, with the main difference being the amount of hydrogen atoms they contain. Saturated fatty acids have much more hydrogen atoms in them. It “stiffens them up” into a more solid substance.
Each kind of oil is a combination of various fatty acids, some saturated and some unsaturated. The more saturated fatty acids an oil has, the higher its melting point. In other words, the more solid it tends to be at room temperature. For example, palm oil, which has mostly saturated fatty acids, is semi-solid at room temperature.
Food companies like oils with saturated fatty acids because they have longer shelf lives and in baked goods provide a better texture and mouthfeel. Lard, by the way is also highly saturated.
Unfortunately, cheap oils like soybean and cottonseed are not solid at room temperature. That’s where the brilliant invention of hydrogenation comes in – bombard the oil with hydrogen atoms until it changes its molecular structure.
If you do it just right, you’ll have created an oil that is solid enough at room temperature, yet still spreadable (margarine anyone?) This is called partial hydrogenation. Do it too much and you’ll get a fully hydrogenated oil, a solid slab at room temperature.
The chemical structure of the unsaturated fatty acids after the partial hydrogenation turns them into trans-fatty acids. But if you go all the way, they turn into the more familiar saturated fatty acids.
Welcome to the wonderful world of organic chemistry.
From a health perspective, it turns out that trans-fatty acids (trans-fat) cause serious health issues, much worse than saturated fatty acids (saturated fat). That’s why despite their culinary and economical allure, in the past few years oils with trans-fats are being used in less products. (Unfortunately, plenty of foods still contain partially hydrogenated oils.)
What to do at the supermarket:
Avoid products with partially hydrogenated oils,because of the trans fat. Limit products with high saturated fat values, whether naturally occurring, or through full hydrogenation.
- Lefevre M, Mensink RP, Kris-Etherton PM, Petersen B, Smith K, Flickinger BD.
Predicted changes in fatty acid intakes, plasma lipids, and cardiovascular disease risk following replacement of trans fatty acid-containing soybean oil with application-appropriate alternatives. Lipids. 2012;47(10):951-62.
- FAQs about Fats – American Heart Association