When I speculated a while ago about what meme would replace the low-carb craze, the trans fat (Salon.com article) one hadn’t yet really surfaced, but it looks like the next big thing. Like those bags of candy that proudly proclaim ‘0% fat’ (loads of suger, will definitely make you fat, but no actual fat), there’s plenty of unhealthy, fattening food that is now proudly gaining the ‘0% trans fat’ label.
Just a quick backgrounder:
Animal fats are mostly saturated. That is, they have a lot of single bonds between the carbon atoms, and each carbon fills up the rest of its bonding sites with hydrogen. (So, ‘saturated’ because they’re full of as much hydrogen as they can take.) Saturated fats are most often solid, like lard, butter and other animal fats, and tend to be unhealthy for us.
Vegetable fats are most often liquid, like olive oil. This is because they are unsaturated: there are double or triple bonds between the carbon atoms, and less hydrogen. Unsaturated fats are healthier for us – they form less plaque in arteries and are less likely to lead to heart disease.
Trouble is, liquid oils don’t work so well for margerine, or for a wide variety of cooking applications. We replace animal fat with vegetable for health reasons, but the vegetable fat doesn’t taste the same or act the same. So the solution is to add some hydrogen to the vegetable oil – the ‘partially hydrogenated vegetable oil’ you often see as an ingredient. That breaks some of the double and triple bonds and makes the unsaturated fats partly saturated, which makes them more solid and more like the animal fats we’re used to.
With me so far? OK, so pure vegetable oils good (which is why mediterranean diets that use olive oil on bread lead to low heart disease rates), pure animal oils bad, partially hydrogenated vegetable oils middling.
The remaining bit we need to talk about is the ‘trans’. This requires a diagram:
(Fats are long chains. In this diagram, the ‘R’s represent the rest of the chain.) With a double bond between the carbons, if the two hydrogens are on the same side (in this diagram the left side) of the double bond, it’s called a ‘cis’ location (which just means ‘same side’). If they’re on opposite sides, it’s a ‘trans’ (‘across’) location. Trans fats are made as part of the hydrogenation of the vegetable oils, but they’re particularly nasty in terms of hardening arteries and causing heart disease.
So, it’s a good thing to get rid of trans fats, I have no problem at all with that. But as you can see, you can have 0% trans fat and still have heaps of fat in a product from animal fats, pure vegetable oil, and even cis fats. No trans fat is quite a different proposition from no fat at all.
The moral of the story, as always, is caveat emptor – let the buyer beware. Oh – and eat a balanced diet and get some exercise, rather than being swept up by this year’s meme.