Partially hydrogenated oil

You know it's bad for you, but if you're wondering what it is, here's a nice description from the New York Times. The whole article can be found here. What I don't understand is why McDonalds can't just go back to frying in beef tallow instead of trying to invent some other unnatural fat.

[Partially hydrogenated oil] is the perfect fat for modern food manufacturers. Produced by pumping liquid vegetable oil full of hydrogen with a metal catalyst at high heat, the fat stays solid at room temperature - an essential trait for mass-produced baked goods like crackers or cakes. But that is the very process that creates the dangerous trans fat.

The shortening-like oil is an industry workhorse. Its smoothness and high melting point make it a great medium for the creamy filling in an Oreo. In the deep-fat fryer, partially hydrogenated oil can take repeated heatings without breaking down.

It also helps products stay fresh longer on supermarket shelves. Small amounts keep peanut butter from separating. It is even found in products promoted as healthful, like Nutri-Grain yogurt bars and Quaker granola bars.

According to one survey on trans fat issued by the Food and Drug Administration in 1999, partially hydrogenated oil was in 95 percent of the cookies, 100 percent of crackers and 80 percent of frozen breakfast foods on supermarket shelves.