stealth fat
n. A type of fat — known officially as "trans fatty acids" or "trans fats" — that doesn't appear on food nutrition labels.
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.
—Sheryl Gay Stolberg, “F.D.A. Calls For Listing 'Stealth Fat' On Labels,” The New York Times, November 13, 1999
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.
—Jodi Kantor, “Turkey Clubbed,” Slate Magazine, November 13, 1999
1997 (earliest)
The other bad kind, transfats, are what experts call the "stealth fat," hidden in many cookies and crackers and most margarines.
—Al Hinman & Laurie Dhue, “Research Shows Some Fat May be Healthy,” CNN, November 20, 1997