It reads like a too-crazy-to-be-true plot line: The girl who had to have part of her colon removed after she mega-dosed fiber on a diet beloved by celebrities and socialites. Around 2016, when she was in her twenties, the woman says, she paid $6,000 to F-Factor, the New York City-based nutrition practice founded by registered dietician Tanya Zuckerbrot that promotes eating fiber as a way to lose weight. The former private client, who asked to remain anonymous for fear of online retaliation by supporters of F-Factor, did not work with Zuckerbrot directly but another nutritionist at F-Factor, who, she claims, prescribed 50 to 60 grams of fiber a day, about twice the 20 to 35 grams a day recommended by the American Academy of Nutrition and Dietetics and other leading health organizations.
The former client says that she told her F-Factor nutritionist that she suffered from Crohn’s disease, an autoimmune condition that causes severe gastrointestinal distress and abdominal pain, among other symptoms, and was told “high fiber was good for [it].”
Some research supports that theory. But once she began the diet, the F-Factor client’s pain worsened, she told me, and she was not losing weight. At this point, she says, she was told to “drink more water” — and to continue eating the 50 to 60 grams of fiber a day. “My nutritionist told me I was an anomaly because I wasn’t losing weight on the diet,” the woman recalled in a phone interview this summer.
After a few months on the diet, she had her yearly colonoscopy, which revealed a significant increase in polyps, abnormal tissue growths for which Crohn’s sufferers are at an increased risk. “My doctors were surprised by how much worse my condition had gotten and I was told I needed a partial colostomy to prevent colon cancer,” she recalled. The only change in her lifestyle during that time period, she says, was significantly increasing her fiber intake for the four months she was on F-Factor. Following her partial colostomy, she went to see a nutritionist who prescribed a diet that was the “opposite of F-Factor,” she says — 10 grams of fiber a day, or about a fifth of what she was eating before.
Having part of her colon removed has caused numerous medical complications, resulting in multiple hospitalizations since 2018, according to medical records reviewed by Rolling Stone. “I had never been hospitalized before starting F-Factor,” she told me in an interview this week. When we spoke over the summer, the former F-Factor private client described the experience as “falling under the spell” of the popular diet. Now, she says, she wants people to know about what she believes are side effects of the F-Factor diet. (She never told her doctors about having gone on the F-Factor diet, and no doctor has told her that doing so caused her health problems. Her new nutritionist, she says, did suggest there was a connection between eating so much fiber and her Crohn’s flare-up.)
She isn’t the only person who believes that more information should be provided to consumers about the F-Factor diet and related products. The alleged side effects from the extremely fiber-intensive diet are now at the center of a lawsuit filed in the Supreme Court of the State of New York on Wednesday by eight former F-Factor customers, naming Zuckerbrot, two entities related to her, and Nutrablend Foods, the manufacturer of F-Factor’s branded powders and bars. The complaint alleges “on information and belief” that F-Factor products have caused “consumers and plaintiffs significant health issues, including…intestinal blockages requiring emergency surgery, gastric pain, rectal bleeding, intestinal bleeding, impaired liver function, malnutrition, hair loss, fecal impaction, exacerbation of gastrointestinal issues, loss of menstrual cycle, development of gallstones and kidney stones, [and] severe allergic reactions.” (The complaint does not indicate which of these alleged health issues the eight plaintiffs allegedly experienced.) The complaint further alleges that the diet company was negligent with respect to “the safety and well-being of consumers and the general public” by not adequately warning about “the dangers of using F-Factor Products in the way Defendants’ encouraged” (including, the complaint alleges, “the risk of disordered eating”). The plaintiffs are seeking monetary damages in an unspecified amount “to recover for the physical and emotional suffering caused by use of the F-Factor Products and to hold Defendants accountable for their actions.”
In response to the lawsuit, Steven Harfenist, an attorney for Zuckerbrot, told the New York Times the new lawsuit “is based on allegations that have been clearly disproven by medical and scientific experts,” and added, “We are very confident these lawsuits will be dismissed.”
The new suit marks the latest chapter in a controversy that kicked off in mid-2020, when Instagram influencer Emily Gellis began posting complaints about the high-fiber diet, sharing hundreds of anonymous posts from former F-Factor clients and customers who alleged they suffered serious side effects from the regimen. (Over the last two and half years, Gellis has retracted one claim from a woman who made up a fake miscarriage story in an attempt to make a larger point about cancel culture.)
The battle between Gellis, F-Factor founder Zuckerbrot, and their followers continued even after Zuckerbrot and F-Factor brought one defamation lawsuit against Gellis in October 2020 and another in March of this year. In March, Judge Joel Cohen of the New York Supreme Court issued a ruling in Zuckerbrot’s first lawsuit, allowing her defamation claim and a product disparagement claim to continue. Pointing to what he called a “barrage” of Instagram posts leveling serious accusations against Zuckerbrot and F-Factor, “often in intensely personal and vulgar terms,” Judge Cohen rejected Gellis’ argument that the case should be dismissed and ruled among other things that Zuckerbrot sufficiently alleged that Gellis had acted with “actual malice” — in other words, knowing that what she and the anonymous posters said about F-Factor and Zuckerbrot was false or recklessly disregarding whether or not these statements were false. (The judge also rejected Gellis’ argument that she should be protected by Section 230 of the 1996 Communications Decency Act, a federal law established to protect online publishers from liability for third-party material on their sites. As it applies to Gellis’ reposts, at least one legal expert views this part of the ruling as a mistake.)
The latest complaint filed Wednesday against Zuckerbrot and F-Factor alleges that F-Factor products were defective in manufacturing, distribution, inspection, and marketing, among other areas. F-Factor’s nutritional powder has some of the highest concentration of fiber compared to similar products on the market (Metamucil, for example, has around half the amount of fiber), yet, the new complaint alleges, the company has failed to properly warn consumers about the possible side effects of ingesting so much fiber. Even Peter Costello, the former chief operating officer of F-Factor who left the company last year, replied to customer feedback on Facebook that a warning about gastric distress was “an interesting idea that we will fully evaluate,” according to screenshots shared by Gellis and reviewed by Rolling Stone.
“The dosing on F-Factor is obscene,” says Dr. Eric Goldstein, a physician at New York Gastroenterology Associates, who says he has treated a number of people who have done the diet and suffered from side effects including unsafe weight loss, constipation, and cramping. “If you look at the average market standard for fiber powders, it’s four, five, or six grams per serving.”
One sample day on F-Factor, promoted on the company’s social media page, consisted of 78 grams of fiber from both powder and whole food sources. Supplements, Zuckerbrot has noted, “are a simple and healthy way to ensure you meet your needs when you aren’t getting [fiber] from whole foods.” Many doctors and nutritionists agree — but the sheer amount of fiber is a concern to some. To put F-Factor’s recommended dosage in context, the 50 to 60 grams of daily fiber that the former private client of F-Factor with Crohn’s disease says she consumed is “enough for four days,” Goldstein says. While he did not treat her or see her medical records, Goldstein tells Rolling Stone that “it’s plausible that a person could have colon damage from an excess of fiber.”
None of the medical conditions listed in the Oct. 12 complaint have been proven to be linked to F-Factor products. Discussing the controversy on a recent podcast with host Dr. Danielle Bellardo, a cardiologist, Dr. Kevin Klatt, a nutrition researcher and registered dietitian, said that it seemed “overwhelmingly implausible” that F-Factor’s standard recommendation of 35+ grams of fiber daily for women, 38+ grams for men could have caused sort of colon damage a former F-Factor client reportedly suffered, saying there must have been an underlying condition. And, to “correct the record” about the allegations in Gellis’ Instagram posts, F-Factor claims that “out of 174,000 distinct orders in the last 2+ years, we have had only 50 health-related complaints, less than .03 percent of total orders.” (The new lawsuit counters by alleging that this statement is “false based on information and belief” and that Zuckerbrot made the claim “in order to mislead consumers, including Plaintiffs, into believing F-Factor Products are safer than they actually are.”)
However, the new complaint alleges that Zuckerbrot failed to warn customers, including the plaintiffs, of the possible dangers of consuming F-Factor products, by not including warnings on packaging as to proper usage, and telling consumers “that if they want to learn how to use the F-Factor powders properly, they must purchase Defendants’ book The F-Factor Diet.”
Zuckerbrot has made her position on fiber intake clear to her more than 100,000 Instagram followers: “There are no upper-limit recommendations to fiber intake,” she wrote, repeating what’s published in F-Factor’s FAQs. In 2018, a follower direct-messaged the F-Factor founder asking, “Is there such a thing as too much fiber? What is the most amount of fiber you would recommend a day?” According to screenshots Gellis shared with Rolling Stone, Zuckerbrot responded: “There is no such thing as too much fiber, stick to however much your stomach can handle and if you eat a lot of fiber be sure to drink tons of water. The recommended amount is not more than 80g per day.”
However, in private, Zuckerbrot has conveyed a slightly more nuanced message According to a direct Instagram message Gellis shared with Rolling Stone, another former private client, Zuckerbrot advised that client to balance the high quantities of fiber — which can sometimes have a constipating effect — with “Colace [a stool softener] and lots of water.” (In response to this allegation, Zuckerbrot says: “Fiber combined with adequate fluids lead to soft stools that are easy to pass which is why laxatives and stool softeners are not part of the F-Factor Diet. Since fiber is the cornerstone of F-Factor, I would never recommend any patient take Colace, or any stool softener, regularly. In a case where a patient did experience constipation then I would recommend a stool softener, like Colace, to alleviate discomfort. However, if a patient were experiencing chronic constipation, I would refer them to a gastroenterologist to explore an underlying etiology.”)
Zuckerbrot’s anonymous superfan Instagram accounts have joined the fray, with some seeming to view the alleged health issues as almost comical. In response to a call for plaintiffs to join the lawsuit that was filed today, one account responded: “Never knew you could sue for farting. Cabbage farmers, watch out.”
But why on earth would anyone want to ingest copious amounts of fiber? Because, for many, the diet really works. F-Factor clients — including celebrity clientele — have lauded the diet (and Zuckerbrot) for “going the extra mile” and “helping to lower cholesterol.” In a testimonial on the F-Factor website, media personality Donny Deutsch calls himself “a satisfied client and a huge fan,” because the diet “works without compromising my lifestyle.” The confection store entrepreneur Dylan Lauren gushes that “Tanya did the impossible — she helped me clean up my diet, lose weight, and feel healthy, without giving up occasional indulgences in candy.” And the actor Brian Dennehy says he lost 90 pounds on F-Factor, adding, “This is the best I’ve felt in years!”
Some medical and nutrition professionals, too, have commended Zuckerbrot’s approach to health and wellness, pointing out that most Americans do not get enough fiber and its myriad of health benefits. Jermone Zachs, assistant clinical professor at Mount Sinai, praised Zuckerbrot’s “scholarly approach” as a “gift that gives forever.” (According to the newly filed complaint, Zuckerbrot has allegedly compared herself to Mother Teresa.)
Zuckerbrot, it seems, has found the ultimate hunger hack with this nondigestible nutrient. “F-Factor makes you feel full on a very low-calorie diet,” explains Tamara Duker Freuman, a registered dietitian specializing in gastrointestinal issues who routinely treats patients with side effects from high-fiber diets including F-Factor.
F-Factor’s tagline, “Dine Out. Eat Carbs. Drink Alcohol,” sounds pretty appealing. But, as one New York City dietician put it, “any diet that encourages wine but not bananas is, no pun intended, absolutely bananas.”
For many F-Factor acolytes, it’s not just a high-fiber diet they buy into — it’s the glamorous lifestyle that Zuckerbrot (who, as alleged in the new complaint, has charged more than $1,000 an hour for her services) broadcasts frequently on Instagram. There she is gallivanting on the best beaches in the world, from Mykonos to the Seychelles, showing that a middle-aged mom of three can still wear string bikinis, or dining at trendy restaurants in Aspen, St. Barth’s, and Capri. Her feed seems to play on the aspirations of her clientele to have “the perfect life,” with thinness being a key factor.
For a time, Zuckerbrot also perpetuated thin as an ideal by posting quotes like, “What you eat in private, you wear in public.” While she no longer promotes content like that, F-Factor still sells an F-Factor intentions bracelet, which Zuckerbrot says should be worn “on the hand that holds the fork, reaches for the bread basket, or dips into the candy bowl.”
Explaining her business philosophy to the New York Post in 2010, a few years after she set up her practice, Zuckerbrot said, “People will do anything to lose weight….People go on Survivor and eat bugs. If you want something badly enough, you do it.” Cue the former private client who went to Paris with her husband and wouldn’t eat any bread, and other followers of the diet who say they are still afraid of bagels, bananas, and pasta. (The new lawsuit alleges “the use of F-Factor Products and associated diet plans can result in disordered eating and the development of eating disorders.”)
Goldstein recently told me that he was struck by the psychological impact of the diet on the former clients he has treated. “There is this sense from people who have participated with F-Factor,” Goldstein says, that “if you aren’t losing enough weight, you are doing something wrong.”
One woman, an educator in her forties, recalls “getting kind of righteous with friends about the diet.” After all, she had lost 20 pounds in three months by adding more fiber to her meals. (“I looked amazing,” she told me when we spoke last month.) The F-Factor high began to wear off when the educator, who asked to remain anonymous, passed a kidney stone the size of a quarter.
“I was prone to [kidney stones],” she admits, but she believes her condition was “exacerbated by the amount of GiGi crackers, spinach, and berries I was consuming on the diet, leading to a buildup of calcium oxalate.” (Her medical records have been reviewed by Rolling Stone and do show high levels of calcium oxalate. Kidney stones were mentioned as an alleged side effect of F-Factor in the new complaint.)
Yet even passing a kidney stone, an experience some have compared to having a baby without an epidural, didn’t put her off F-Factor. In January 2020, she sent Zuckerbrot a direct message on Instagram asking what she could do to continue eating the F-Factor way without risking building up another kidney stone, according to a screenshot she shared with me. Zuckerbrot, she claims, never wrote back. “The diet really should come with better warnings,” the educator now says.
Some might say that followers of the diet should have consulted their doctors and been more responsible consumers. But Zuckerbrot, a registered dietician with a degree from New York University, one of the top food science programs in the country, positions herself as an authority on nutrition — highlighting the inherent risks of any health professional selling a one-size-fits-all diet on social media. (When asked in 2020 by Today host Sheinelle Jones whether customers are aware of the documented side effects of a high-fiber diet, Zuckerbrot replied, “In the F-Factor book, we encourage people to introduce fiber slowly,” adding that “there is also a warning on our package that says if you are going to use the products for weight management, please read the F-Factor book.”)
Another follower of the F-Factor diet wrote to Zuckerbrot telling her that when she ate 40 grams of fiber in a day, her stomach started to hurt and that she occasionally threw up. According to screenshots shared by Gellis with Rolling Stone, Zuckerbrot wrote back saying that she should introduce fiber slowly, drink lots of water, but that her body should adjust soon. “Give it a few weeks,” she said, signing off with her trademark green heart.
The hitch is that many people don’t adjust, says Duker Freuman, who works at New York Gastroenterology Associates: “Everyone’s GI tract is very different. When the human body evolved, it didn’t involve digesting concentrated mega-doses of fiber.”
One origin story Zuckerbrot offers about F-Factor’s fiber powders — a product line that was launched in 2018 and branded “20/20” to denote their 20 grams of fiber and 20 grams of protein per serving — is that they were developed as a way for the large segment of dieters who missed carbohydrates to be able to eat muffins, waffles, and cookies during the most restrictive phase of the diet, which allows a maximum of around 1,200 calories a day. (Zuckerbrot and the F-Factor website make a point of noting that one doesn’t need to buy the F-Factor powders to follow the F-Factor program.)
“I dare you to eat more than two cups of beans before you want to lie on the couch and die,” says Duker Freuman. “With whole foods, like fruits and vegetables, it’s a real challenge to get past 35 to 40 grams of fiber [per day] because the volume from their bulky fiber and high water content fills you up so quickly.”
F-Factor’s powders — which currently are available in vanilla, chocolate, and unflavored variations, and sell for $50 per bag — contain much more concentrated fiber than in any single serving of unadulterated food, enabling mega-dosing on fiber. Zuckerbot demonstrated to followers how you can add the 20/20 powder to salad dressing, vodka pasta sauce, muffins, macaroni and cheese, French onion soup, and the many other recipes the diet brand promotes. Until around the spring of 2020, she said the company was selling $1 million a month of the powder. An enterprising businesswoman, Zuckerbrot claims she was sui generis as the first registered dietician to have her own line of grocery products (high fiber bars) in national distribution.
“It was all in the marketing,” observes Duker Freuman, referring to F-Factor’s products. “The ingredients in the powders are all ones you could cobble together from Whole Foods at a fraction of the price.”
In Zuckerbrot’s second defamation suit against Gellis, filed in March, she claims that “Gellis’s social media misconduct has caused Zuckerbrot to suffer reputational damage and devastating emotional distress.” Still, Zuckerbrot continues to promote her diet plan and F-Factor’s products, and frames the controversy as a smear campaign started by jealous competitors out for financial gain. Zuckerbrot has characterized the controversy on several Instagram lives as “the worst example of cancel culture.”
The new lawsuit, which names Zuckerbrot as a defendant, alleges she released a statement calling people’s concerns about the diet “rumors and lies,” claiming she went on to delete negative comments from F-Factor’s social media accounts (something, according to screenshots provided by Gellis and reviewed by Rolling Stone, the company’s former COO, Costello, admitted to doing). When asked in the 2020 Today interview about negative comments being deleted, Zuckerbrot said: “We follow the guidelines set forth by Instagram and Facebook, and we have deleted comments that were slanderous in nature, but we take health issues seriously.”
The suit alleges that “a team of Internet bullies…shamed and harassed those who were brave enough to speak out against the F-Factor Products.” Referring to three accountability accounts and claiming that the “Defendants have promoted these accounts to their social media followers,” the lawsuit claims that these accounts operate at the direction of the defendants. The plaintiffs also allege that “Defendant Zuckerbrot, through her Instagram account… has threatened people with legal action for stating that F-Factor Products are ‘unsafe.’” This “campaign” was, according to the lawsuit, allegedly done to “increase the public perception of F-Factor Products and continue to increase sales.”
Zuckerbrot often comes off as incredulous that anyone would have the gumption to question the safety of her powders or her diet. On one Instagram live, while stroking her hair, she argued that, if she hasn’t lost her hair, it’s hard to believe that others might have had that side effect from the diet. And if Zuckerbrot and her family are so healthy while, as she claims, they use more F-Factor products than anyone, how could their powders have possibly made other people sick?
On more than one occasion, Zuckerbrot has cited the company’s certificate of analysis (COA) and independent testing of the powders, which showed they are safe to consume. However, the Oct. 12 complaint alleges that “F-Factor Products also contain elevated levels of heavy metals, including lead.” (Rolling Stone had the unflavored and vegan powders independently tested through the Clean Label Profit, a food safety nonprofit, and the results showed evidence of lead in the powders — something that is disclosed on the packaging with a California Prop 65 Warning required for products that have exposure to chemicals and heavy metals that can cause cancer, birth defects, or other reproductive harm. The complaint does not allege that these levels of lead are dangerous.)
The plaintiffs’ allegations in the just-filed suit suggest that the COA and lab results don’t give the full picture, as they reflect the products’ quality but don’t address concerns about the mega-doses of fiber consumers are being encouraged to consume. The issue, the plaintiffs claim, is about product safety and the instructions given to F-Factor consumers about their usage. “Any healthcare provider has an honor bound to present the downsides or negative effects of an intervention,” says Goldstein. “Even a normal high fiber diet is not without consequences.”
Fiber powders and other supplements exist in a regulatory Wild West where the FDA has little oversight; there is scant control over the multibillion-dollar supplements market. F-Factor, like other companies that manufacture supplements, is not required to provide the FDA with information about its products. Illinois senator Dick Durbin has proposed legislation, the Dietary Supplement Listing Act of 2022, to change this and help tighten oversight on the estimated 80,000 different supplement products that are sold in the United States. “Our bill will give the FDA the information it needs to protect Americans from dangerous products being sold as health supplements,” Durbin said in April.
What is curious is that for a controversy that has potentially such weighty public health implications, the war between Zuckerbrot and Gellis has been framed with some degree of detached bemusement, almost as a punch line. The so-called fiber feud has been compared to the Real Housewives, reduced to nothing more than an Instagram snipe-off between two privileged white women.
“I think people make light of it because much of it has played out on social media, a platform people see as frivolous despite its obvious power in the marketplace,” says Jo Piazza, host of the podcast Under the Influence, which explores influencer culture. “It is also dismissed because the majority of the players are women. If they were men this would be taken much more seriously. There are real consequences to the health allegations being levied, and yet so many people would rather boil it down to a catfight.”