At this point in time there is unanimity that trans fats are a problem," said Dr. Walter Willett, chairman of the nutrition department at the Harvard School of Public Health. "We sometimes refer to them as a stealth fat because you eat them and they are not on the label.

Parkay and Entenmann's beware: The LAT and NYT front new FDA guidelines that, if accepted, would include a count of trans fatty acids—aka "stealth fat"—on nutrition labels.

The other bad kind, transfats, are what experts call the "stealth fat," hidden in many cookies and crackers and most margarines.