Jillian Michaels of "Biggest Loser" fame has been sued for a second time in as many days over a weight loss product a consumer claims is "worthless."

Stephanie Creer claims in her class action lawsuit she has struggled with weight loss her entire life and was "intrigued" into purchasing the product Calorie Control because Michaels was endorsing it.

You know the story ... Creer didn't lose a pound so she's suing.

What's interesting ... the suit is almost a verbatim copy of another class action suit filed against Michael's yesterday -- a suit which also alleges Calorie Control is bogus. But this suit was filed by a different set of lawyers.

After the first suit was filed, Michael's rep told TMZ the product was vetted by experts before Jillian put her name on it and she is confident she'll prevail in court.