We Asked Some R.D.s What They Really Think About the F-Factor Diet (2024)

You may have seen news swirling about the F-Factor diet over the last few months. ICYMI: The F-Factor diet is a high-fiber diet intended for weight loss and created by Tanya Zuckerbrot, M.S., R.D. Since publishing The F-Factor Diet: Discover the Secret to Permanent Weight Loss in 2006, Zuckerbrot has built a high-profile brand around the diet—at various points attracting celeb followers like Olivia Culpo and Megyn Kelly, serving as the official dietitian to the Miss Universe Organization, becoming a media personality, and running the F-Factor company, which offers nutrition counseling services, diet plans, high-fiber products, branded clothes and accessories, and an app.

This summer, fashion influencer Emily Gellis spoke out publicly about what she believed to be the dangers of the diet, sharing purported screenshots of anonymous Instagram DMs from people who say they experienced a variety of physical and psychological symptoms while on the diet (and/or consuming the F-Factor brand’s fiber-protein powder). Since then, outlets including the New York Times, Insider, and Refinery29 have spoken to several individuals who say that their issues like GI distress, hives, eating disorders, hair loss, and amenorrhea (absence of menstruation) may be linked to the diet—although, as Insider notes, these stories “are anecdotal and don't prove causation.”

Zuckerbrot has categorically denied these allegations. On October 8, 2020, Zuckerbrot’s lawyers announced that she and F-Factor as a company were filing a lawsuit against Gellis for “publishing over 4,500 false, defamatory and/or harassing statements'' starting in July 2020, according to a press release. The suit claims that F-Factor’s monthly sales revenue dropped from $1,000,000 to $90,000 since July. Gellis filed a counterclaim seekingto dismiss Zukerbrot'ssuit. “I have not defamed [Zuckerbrot] and I will do everything I need to do to assert my innocence,” Gellis told the Times. (Representatives for Gellis did not respond to SELF's requests for comment.)

So let’s look at the actual diet behind all the headlines. It is, after all, a part of the diet industry and diet culture that we often critique at SELF for its role in idealizing thinness and whiteness, promoting disordered eating, and skewing our idea of health, among other things. We asked a few registered dietitians (none of whom have treated clients who have followed the diet, or can speak specifically to the allegations) for their take on the diet, and what we can learn from it.

What the F-Factor involves, and how it works

Zuckerbrot positions the F-Factor diet as a unique, science-based “liberating” and “sustainable” approach to weight loss and good health. “F-Factor is not a restrictive ‘fad diet,’” an F-Factor representative tells SELF via email. “For over 20 years, the program has been helping thousands of people lose weight, achieve good health, and maintain a nutritious diet,” the representative continues, later adding that the diet has also helped people to “safely manage” their weight.

The diet supposedly works by “combining lean proteins with high-fiber carbohydrates, which are low in calories and keep you feeling full throughout the day,” according to a site page titled "What Is F-Factor?" “Typical feelings of hunger and deprivation that are usually associated with weight loss are eliminated with the F-Factor Program.” This is supposed to be largely thanks to the “miracle status” of fiber.

Step one, which lasts two weeks and is described as the most restrictive phase of the diet, is supposed to “jump-start” your weight loss. The “average caloric intake is anywhere from 900 to 1,100 calories per day,” Zuckerbrot explains in The F-Factor Diet book. To stay under 35 grams of net carbs a day, you are permitted three serving sizes of specified high-fiber carbs. You can also eat “as many non-starchy vegetables as you like, and 2 to 6 ounces of lean or very lean meat or meat substitute” per meal, according to the book. However, “unrestricted” non-starchy veggies must be “raw, plain or steamed with no oil,” according to the site. And the list of foods to avoid in step one is pretty long: bread, cereal, grains, beans, peas, lentils, pasta, rice, pastries, crackers, most snack foods, baked goods, corn, peas, sweet potatoes, potatoes, yams, fruit juice, medium- and high-fat meats, and all dairy except for plain and nonfat Greek yogurt, Icelandic yogurt, or quark (which count as lean proteins).

Step two allows for a wider variety of foods and three additional servings of carbs (15 grams each). This raises the built-in calorie cap by about 240 when you add in accompanying calories from the increased protein and fat to go along with step two's higher carb intake. The idea is that this calorie increase will prevent your body from thinking it is starving and potentially slowing down your metabolism (which would impede weight loss), the book explains. You remain on step two until you reach your intended “goal weight.”

In step three, you begin the “maintenance phase” that you stay on for the rest of your life. Along with getting three more additional servings of carbs, you’re allowed to eat a small serving of just about anything as long as you continue to stay within the carb and fiber parameters. (“Even a small portion of pasta...isn’t going to get you into trouble,” the intro to step three reads.) And even in the maintenance phase, the diet recommends curbing the intake of certain highly nutritious foods because “there is a difference between healthy and healthy for weight loss,” according to the site. That includes satiating and calorie-dense fats like olive oil, avocados, nuts, and seeds. Similarly, the diet favors low-fat and skim versions of dairy products and calls out ancient grains (like quinoa) for being detrimental to weight loss. “Essentially, the health benefits of ‘health foods’ can be outweighed (pun intended) if they’re so caloric that they cause us to gain weight,” as the page on ancient grains reads.

To meet the dietary requirements and keep weight loss (and weight maintenance) on track, followers are encouraged to consult the F-Factor app or book for recommended foods and portion sizes, and record all of their food and macronutrient intake via food journaling or the app. The company also sells an Intentions Bracelet that is meant to serve as a “daily visual reminder to honor your intentions for looking and feeling your best so that you never settle for mediocrity”—in other words, to apparently help you avoid making food choices that could prevent weight loss or cause weight gain. The packaging tells you to wear the bracelet on the wrist of your dominant hand: “This is the hand that holds the fork, reaches for the bread basket, or dips into the candy dish,” it reads. “This is the hand that will either undermine your intentions or honor them.”

What concerns some R.D.s about diets like F-Factor

The R.D.s we talked to had concerns about various aspects of the F-Factor diet, mostly surrounding what they saw as its restrictiveness and its emphasis on fiber. We grouped what they said into four main critiques.

1. They can be restrictive and hard to follow.

The F-Factor diet is a great example of “diets [that] parade around as an example of ‘liberation’ and ‘flexibility,’ when they are anything but,” Rachael Hartley, R.D., certified intuitive eating counselor and owner of Rachael Hartley Nutrition, tells SELF. “This way of eating is extremely restrictive,” Shana Minei Spence, M.S., R.D.N., C.D.N., founder of The Nutrition Tea, tells SELF. And “the more restrictive a diet is, the less likely it is that people will find it sustainable.” In response to the claim that F-Factor is restrictive and may not be sustainable, a company representative says, “F-Factor’s message is not about restriction, but rather the focus is on adding fiber-rich foods into your diet for fiber’s medically proven health and weight management benefits. From Day 1, F-Factor encourages breakfast, lunch, snack, and dinner and discourages skipping any meals.”

However, many of the eating behaviors involved in adhering to the F-Factor protocol—restricting calories; meticulously counting and recording grams of carbs and fiber; constantly consulting lists of what you can and can’t eat; declining “too much” quinoa, almonds, or veggies cooked in olive oil because the portion size is too caloric—are hallmarks of the type of restrictive weight-loss diets that many R.D.s caution against precisely because of how difficult and unsustainable they can be.

Take calories, for instance. While there are not formal calorie limits in the diet, the average number of daily calories people consume following the diet (according to the book) is quite low, and not enough to be a healthy amount for most adults, Spence says. (Again, as few as 900 calories in step one, with an additional 240 calories, from three more carb servings and additional protein/fat, added per step.) While, of course, calorie needs vary widely based on factors like age, sex, and physical activity, an average woman in her 20s generally needs about 2,000 calories a day for adequate energy, according to the United States Department of Agriculture’s Dietary Guidelines. Not getting enough energy from food can deprive people of the mental and physical energy their brains and bodies need to function well throughout the day, Spence explains.

Because of how the diet is positioned, people may begin the diet expecting a freeing and empowering lifestyle—and may soon find that their actual lived experience trying to adhere to it to be something pretty different, Spence explains. Take the diet’s policy on dessert, for example. While the About page insists, “You will be able to indulge your sweet tooth,” a page about calorie-counting on the site puts strict conditions on that indulgence during step one: “We don’t recommend getting in the habit of having dessert every night, but if you must indulge, and you have not exceeded your daily net carb allotment, be sure it is under 100 calories, and less than 15g net carb.” You might say this stretches the meaning of the word “indulgent.” At the end of the day, “Whenever you have to count on a ‘plan’ or follow a set of rules when eating, the last thing it should be described as is freeing,” Spence says.

2. Fiber is not a miracle nutrient.

Now, let’s talk more about the star of the F-Factor diet. Fiber is generally awesome for our bodies, and most Americans don’t eat enough of this key nutrient. There are two types of fiber: soluble and insoluble. You can read a lot more about how they work and what they do here, but together they help regulate digestion—preventing constipation (by speeding things up), moderating blood sugar spikes (by slowing the rate at which sugar enters the bloodstream), lowering LDL cholesterol levels (by attaching to dietary fat and cholesterol molecules), and promoting feelings of fullness (by adding bulk), as SELF has previously reported. That’s why eating more fiber-rich foods is actually one of the most routine dietary recommendations that R.D.s and doctors make. Pretty much every major health organization you can think of espouses the benefits of the nutrient: The USDA, the Academy of Nutrition and Dietetics, the Institute of Medicine, the American Heart Association, and the American Diabetes Association.

But the F-Factor diet goes quite a lot further than “eat more fiber”—dubbing it a “miracle carb” and selling it as something of a magic gateway to weight loss. (Zuckerbrot actually published a second book in 2012 titled The Miracle Carb Diet: Make Calories and Fat Disappear—with Fiber!) The R.D.s we spoke to were critical of this hyperbolic language because they say it misrepresents what fiber actually does in our bodies. “Yes, fiber is filling, but stating that [it makes] fat and calories magically disappear is incorrect and quite frankly misleading,” Spence says. (According to an F-Factor representative, “F-Factor recommends that all meals are a combination of high-fiber carbohydrates, protein, and healthy fats.”)

Beyond that, the experts we spoke to are concerned that any formal eating plan that glorifies and hyper-focuses on a single nutrient could ultimately do more harm than good. “It takes this kernel of truth, that fiber is good for you, then blows it up to where it's no longer helpful,” Hartley says. The diet does not present a balanced view of nutrition, according to Spence, which can contribute to a distorted perspective on healthy eating. Fixating on fiber above all else when our bodies need a wide variety of nutrients from a bunch of different foods isn’t balanced or healthy, Spence says.

3. There can be such a thing as too much fiber.

“A very generalized rule of thumb is that too much of anything can have a negative effect on our bodies,” fiber included, Spence says. The Dietary Guidelines recommend people aim for roughly 14 grams of fiber for every 1,000 calories in their diet (so about 28 grams if you eat 2,000 calories, for instance). While there is no upward limit set for fiber intake, too much can cause digestive issues like stomach discomfort, bloating, and gas, as SELF has previously reported, and especially when not consumed with enough water. The diet does recommend increasing fiber intake gradually in the beginning and drinking three liters of water a day. But if people don’t slowly add more fiber to their diets while also increasing their water intake, that can result in some GI issues.

“Personally, I have not worked with clients who have attempted this specific dieting protocol, so I’ll refrain from speaking to that,” Cara Harbstreet, M.S., R.D., L.D., of Street Smart Nutrition, tells SELF. “But what I can say is that often when someone shifts to eating large amounts of fiber, the GI effects can be very uncomfortable.” And while eating a lot of naturally occurring fiber can cause problems, it’s much easier to overdo it when it comes to products with added fiber, as SELF has previously reported, because of the extremely high concentrations of fiber they can contain. The F-Factor brand protein powders and bars all contain 20 grams of fiber per serving (mostly from partially hydrolyzed guar gum or soluble corn fiber), which some R.D.s say is a lot of fiber for your GI system to handle all at once.

4. The Intentions Bracelet may promote an unhealthy focus on every bite you eat.

The Intentions Bracelet that’s apparently meant to help people hold themselves accountable may be problematic for some people, Spence says. The bracelet’s function is effectively to serve as a near-constant reminder to think of their food choices, their weight, and avoiding “mediocrity.” “It's pretty much encouraging disordered eating,” Spence says.

The flaws of weight-loss diets like F-Factor in general

There’s plenty that these R.D.s are critiquing about the F-Factor diet generally, but many of their criticisms could apply to countless other weight-loss diets. "It's important to note that the problems aren't just with F-Factor,” Hartley says. While weight-loss diets may vary in their style and rules, it’s pretty standard for these diets to offer “magic” solutions, misleading messaging, and restrictive eating. And they’re all a part of the same diet industry that has serious implications for the way we think about weight, health, what bodies we deem desirable, and our relationships with food.

These kinds of diets can oversimplify weight loss, conflate it with health, and prioritize it over other aspects of well-being. The fact is that weight loss in and of itself is not a healthy goal for many people. It’s often an imperative of diet culture more than medical science, which offers a much more nuanced view of the relationship between weight and health. Plus, weight is in part determined by factors other than your diet, like genetics, socioeconomic status, and medical conditions. On top of all that, most weight-loss diets don’t even deliver on the long-term weight loss they promote. There is evidence that weight loss from dieting can cause physiological adaptations that actually cause weight regain down the road, like changes in levels of energy expenditure and appetite-regulating hormones—throwing into question the idea of an effortless “maintenance phase.”

This issue is compounded by the fact that overwhelmingly, the people selling a particular weight-loss diet are living in thin, white, multi-privileged bodies, Harbstreet points out. And when that person has “R.D.” or another professional health credential next to their name, people are inclined to trust what they say about weight and weight loss. “Though it’s never explicitly said, the tone is that ‘if you eat/live like me, you can look like me,’” Harbstreet says. “This disregards the large genetic component that contributes to body size and appearance, and promotes the harmful thin ideal,” Harbstreet says.

This can all have a negative impact on the health and well-being of people caught up in trying to lose weight on these diets. While, of course, any weight-loss diet can be detrimental to physical health if it restricts macronutrients, food groups, or calories in a way that deprives the body of the energy and balanced and varied nutrition it needs, dieting can also take a serious toll on people’s mental health. Restrictive dieting in pursuit of weight loss can help cultivate a fraught relationship with food and body image that, at best, can cause stress and diminish the joy of eating—and, at worst, promote disordered eating behaviors or contribute to the onset of an eating disorder (especially in combination with other risk factors). There is also the emotional distress of feeling like you failed. “Diets always start off as exciting because people are thinking that this is the answer for them,” Spence explains. But if the weight doesn’t come off or stay off as easily as promised, as is usually the case, it’s a set-up for frustration, disappointment, and self-blame, Spence says.

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