IT'S never pleasant to learn that an artificial substance in your food might be ruining your health. This is what happened with trans fats when they were "discovered" in the food supply a few years ago, after a high-profile lawsuit against the makers of the Oreo cookie (laden with trans fats, who knew?) captured headlines nationwide. The publicity pushed the Food and Drug Administration to require that trans fats be listed on package labels starting this year. Producers of cookies, cakes, crackers, frozen foods and margarines, all high in trans fats, thus had an incentive to eliminate them from their...