LOS ANGELES — Jillian Michaels has been sued for alleged false advertising by a woman who claims she was duped into buying a diet supplement endorsed by the celebrity trainer.

Christie Christensen, of Lake Elsinore, Calif., is seeking class-action status for the case she filed Tuesday in Los Angeles. Michaels is a hard-charging, no-nonsense trainer best-known as one of the stars of NBC’s hit reality show, “The Biggest Loser.”

Christensen’s lawsuit claims she bought a product called “Jillian Michaels Maximum Strength Calorie Control” last month and that it has failed to lessen her appetite or cause her to lose weight as advertised.

The product and a Web site advertising include the claim, “Two Capsules Before Main Meals and You Lose Weight … That’s It!”

“Ms. Michaels knows better — taking two pills before eating does not miraculously cause weight loss,” the lawsuit states.

Christensen’s suit seeks unspecified damages that are not expected to total more than $5 million.