Trans fat (also called trans fatty acid) is created when vegetable oils are hydrogenated. The process saturates the oil and produces trans fat. It also gives margarine its butter-like consistency.
The National Academy of Science has reported that trans fat in food presents a significant health risk for coronary disease. Recent studies also show that trans fat increases the level of LDL cholesterol ("bad cholesterol"), while simultaneously lowering the level of HDL cholesterol ("good cholesterol").
Based on this research and the potential adverse effects of trans fat, the FDA requires nutritional labeling for the presence of trans fat in food products. Products that contain 0.5 g or more per serving are required to list the trans fat content. Small amounts of trans fat are naturally present in some dairy products, including butter. Challenge butter products contain less than 0.5 g per serving.