In thousands of Instagram posts, which have included video monologues and screenshots of messages between Ms. Gellis and often anonymous dieters who followed the F-Factor plan or bought products from the company, Ms. Gellis asserted that F-Factor products were causing rashes and other ailments. She also accused Ms. Zuckerbrot of encouraging disordered eating habits, both through the dietary advice she dispensed and the company culture she cultivated.
Ms. Gellis also told her followers that she had been contacted by sources who linked their miscarriages to the F-factor diet and products. One of those sources told The New York Times in August that she fabricated the story.
Today, lawyers for Ms. Zuckerbrot said they filed a lawsuit in New York, saying that Ms. Gellis has cost her business millions of dollars in revenue because of more than 4,500 “false, defamatory, and/or harassing statements.” F-Factor was making $1 million a month before Ms. Gellis began posting about the company in July 2020, according to the lawsuit. Now the company’s monthly revenue is less than $90,000.
Ms. Gellis said she plans to countersue Ms. Zuckerbrot. “I have not defamed her and I will do everything I need to do to assert my innocence,” she said in an interview.
F-Factor is a diet consulting business; registered dietitians can be hired to coach clients on Ms. Zuckerbrot’s high-fiber eating plan. It requires its adherents to initially follow a 1200-calorie-a-day meal plan. Clients who worked directly with Ms. Zuckerbrot, who has written two books about the diet, have included high-profile figures such as Megyn Kelly. Some clients have paid as much as $25,000 for Ms. Zuckerbrot’s services. In 2018, F-Factor began selling snack bars and powders as well.
“Gellis’s illegal, abusive, and harassing social media misconduct has caused, and continues to cause, devastating financial damages and enormous emotional distress,” the lawsuit says.
Ms. Zuckerbrot is represented by Dan K. Webb, a former United States attorney who has built a private practice focused in part on suing media entities for defamation against companies that sell food. Last summer, Mr. Webb was named as a special prosecutor tasked with investigating the Jussie Smollet case.
The F-Factor products, Mr. Webb said in an interview, “are completely safe and the diet is safe. Ms. Gellis went on a vendetta to try to destroy this company — and she did succeed.”
Ms. Gellis learned of the lawsuit when she received a message on Instagram from a New York Post reporter asking for her to comment.
She addressed Ms. Zuckerbrot directly on Instagram, saying in a video today: “Tanya, you are the devil, you’re the devil, and you are going to get what’s coming to you.” Ms. Gellis criticized Ms. Zuckerbrot for revealing Ms. Gellis’s home address in the lawsuit when the filing was posted on the F-Factor website.
Mr. Webb says that it was Ms. Gellis, and not the pandemic and attendant economic consequences, which has zapped F-Factor’s revenue and growth. A spokesman for F-Factor said that in May the company’s gross revenue from product sales were $1.2 million but that in August sales dropped to $254,000 before hitting last month’s low of about $90,000.
Early this year, Evolution V.C. Partners was poised to make a $2 million investment in F-factor, which it valued at $40 million. “That capital investor has completely withdrawn his commitment to make his investment in F-Factor,” the lawsuit says.
Gregg Smith, the principal of Evolution V.C. Partners, said in an interview that he walked away from the deal with F-Factor without being aware of any internet criticism of the brand from Ms. Gellis or others. “I was exploring an active investment in the company in the spring and became distracted with family health issues,” he said.
While Ms. Gellis is the only defendant named in the lawsuit, Ms. Zuckerbrot also blames her company’s problems on Instagram and on Facebook, its parent company, as well. “Gellis’s conduct was facilitated and made possible by Facebook and Instagram, which were repeatedly and comprehensively notified about Gellis’s gross abuse of their platforms,” the lawsuit states. “Nevertheless, Facebook and Instagram knowingly and intentionally refused to take any action.”
Mr. Webb said he is considering future legal action that might include the platforms. “Those companies are not named because of the immunity Congress gave them but I am looking at certain legal theories and we will see where this goes,” he said.
A spokesman for Facebook did not immediately return a request for comment.
In addition to the lawsuit filed by Ms. Zuckerbrot, three sources say that they have been interviewed by a representative of the Department of Justice about their knowledge of the F-Factor’s company practices.
A representative of that office declined to comment.