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Fast forward 20 years, and the latest wisdom says that "transfats" are terrible for you. In fact, they are allegedly so bad, they have actually been outlawed in some places. But where do "transfats" come from? Partially hydrogenated oils. And where does partially hydrogenated oil come from? Corn, soy and other non-animal sources of fat.
In other words, groups like the CSPI ran around 20 years ago demanding we get rid of our perfectly healthy animal fat and replace it with these partially hydrogenated oil alternatives (i.e. margarine v. butter). And it turns out, these "fake fats" are waaaay worse for us.
Sounds too good to be true.
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You seem to be a little confused here.
Animal fats are considered unhealthy because they tend to be high in saturated fats. Saturated fats, like tallow and lard, are solid at room temperature. They tend to come from animal sources; these types of fats are liquid at animal body temperatures.
Unsaturated fats - oils, more properly - are liquid a room temperature. They tend to be found in plant sources.
There are different types of unsaturated fats, depending on where the unsaturated double bond is found, and the configuration of the double bond. Fats with a single double bond are mono-unsaturated, more than one double bond are polyunsaturated. Double bonds can be in the the cis- or trans- configuration. A cis- bond "kinks" the fatty acid chain, a trans- bond is more straight.
Saturated fats, mostly from animal sources and some tropical plants, are not "perfectly healthy". They are, however, more difficult to remove from the diet, so the emphasis has been on trans-unsaturated fats.
Unlike cis-unsaturated fats, trans- fats are not commonly naturally occurring, so it is misleading to state the trans-fats "come from" plant oils. Trans fats are chemically synthesized from cis-fats. This is commonly done to extend the shelf life of oils - double bonds are susceptible to oxidation; poly-unsaturated fats become rancid after a time. This is why trans-fats have come to be extensively used in cooking and for margarines.
But don't be confused. Trans-fats are not particularly healthy, but that should not be taken to mean that saturated animal fats are any more healthy. Both raise LDL levels, but saturated fats are somewhat offset by also raising HDL. On the other hand, saturated fats count for a much higher percentage, and are more prevalent in whole foods; for this reason, the emphasis has been on removing trans-fats - cooking oils and the like.
But you should still watch your saturated fats.