Know it: A mad-scientist project gone wrong, trans fats are created in a lab by partially hydrogenating healthier oils. This process destroys the many good benefits of the original fats. What's worse, consuming trans fats ups your risk for heart disease and metabolic syndrome. Most nutritionists recommend avoiding them altogether, which doesn't sound so hard except current labeling guidelines allow manufacturers to round anything less than 0.5g/serving down to zero. Eat more than a few servings, and you've consumed a significant amount of the Frankenfood.
Avoid it:Anything that says "partially hydrogenated oil," "hydrogenated vegetable oil," or "shortening" on the ingredients list contains trans fats, no matter what the label says.