We all hear about trans fat being bad, but you rarely hear about what it is or why it is bad. I thought about writing it up here, but, frankly, that seemed like a lot of work, and besides, I am not the expert by any stretch. Fortunately, Molecule of the Day, my favorite chemistry blog, read my mind and did a post about trans fats (trans fatty acids, to be precise) the same day that I emailed him my request. Go MOTD! Another good expanation about trans fat. is Wikipedia, especially the discussion page.
It might be a bit much if you don’t have much of a chemistry background, so I’ll try to add my own little explanation: some fat is straight and hard, and some is bent and soft (and we call it oil). Hard fat is bad. This is saturated fat. But we like it because it is good for processed food (including the processing we do at home like baking cookies).
Saturated fat (like butter) is more expensive than oil. So they take the oil, the bent fat, and straighten it out to make it hard. The bends are caused by some double bonds of carbons. Bonds can be bent (called cis) or straight (trans). In nature, they almost always are cis. But with some processing, we can either add some hydrogen to make them saturated fats, or convert the cis double bonds to trans bonds. Both of these changes straighten out the oil, making is harder fat.
This is partially hydrogenated oil, or trans fat. It is shaped like saturated fat, and so it behaves more like saturated fat for food processing, both when we make the food and when our body digests and uses the food. There’s the problem.
Our body sort of thinks that the partially hydrogenated fat is saturated fat because it is straight like saturated fat, but since it isn’t quite saturated fat, it really confuses our bodies in ways we don’t fully understand yet. One thing we for sure knows is that it screwed up our balance of different cholesterols. Saturated fat and trans fat both raises “bad cholesterol,” and trans fat has the bonus effect of also lowering “good cholesterol.” The relationship between fat and cholesterol is another given that we should probably understand more, but I’ll save that for a future post. (I bet you probably didn’t know, or forgot, that cholesterol is a steroid, and that steroids are hormones, and that hormones are lipids, i.e. fats. It’s more complex than that, but they are all related.)
Trans fats are so bad that, unlike regular saturated fats, there is no recommended maximum. Just don’t eat it, or as little of it as possible. That’s why the US now requires that food labels include trans fat in addition to saturated fat and total fat. So look for 0 grams trans fat on the labels and you are set, right? Not quite. There is a catch. The USDA allows manufacturers to round to the nearest 500mg, or half gram. As long as a food has less than a half gram of trans fat per serving, they can put a big zero on that line, even if there is partially hydrogenated oil listed in the ingredients list.
What it comes down to is: look for partially hydrogenated oil in the ingredients list. If it is there, there is trans fat, regardless of what the nutritional information says. And you’ll be surprised how much food has this ingredient once you start looking for it. If you are like me, you’ll find yourself buying fewer and fewer processed foods.
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