Everything You Should Know About the F-Factor Diet, According to Experts (2024)

Editor's Note: Good Housekeeping first covered the F-Factor diet in 2019, in advance of concerns that have surfaced around the diet's influence on healthy eating habits as well as recent allegations that suggest F-Factor brand food products produce negative physical side effects. Below, we've updated our review of the information and advice shared in Tanya Zuckerbrot's 2006 book, The F-Factor Diet: Discover the Secret to Permanent Weight Loss. Our coverage has been vetted by nutrition experts in the Good Housekeeping Institute, and we are continuing to monitor claims made against the F-Factor program and its founder. As we always advise, it's important to discuss any long-term changes to your diet with your primary healthcare provider before implementing lifestyle changes.

The "F" in F-Factor diet doesn't stand for fad. Registered dietitian Tanya Zuckerbrot's book The F-Factor Diet: Discover the Secret to Permanent Weight Loss first came out in 2006, and her fiber-fueled approach to healthy eating has now stuck around for over a decade. Many celebs (like Katie Couric) have tried the plan, and unlike other trendy "detoxes", this method is based on a premise that increasing your fiber intake may help you lose weight — for good.

"What I love about F-Factor is that it creates a plan in which eating real, wholesome foods and prioritizing nutrient-dense meals and snacks is simple and adaptable to your personal needs and habits," Jaclyn London, MS, RD, CDN, told Good Housekeeping in 2019.

Zuckerbrot, the founder and CEO of the F-Factor brand, says her company has helped nearly 175,000 dieters begin a new program in recent years, but the company has evolved past a singular diet plan. Since the F-Factor program is focused on maximizing fiber consumption (hence the "F"), Zuckerbrot's company also introduced fiber supplements and ready-to-eat products as a new offering to customers. According to a recent report published in the New York Times, Zuckerbrot has faced some criticism online as former clients and customers have alleged that F-Factor products have led to adverse physical side effects over the years — and others claim that some messaging may promote unhealthy eating habits over time.

Here's everything you should know about the F-Factor diet program before you purchase a book, plan, or any of its products.

What is the F-Factor diet?

The F-Factor diet prioritizes upping the amount of fiber you consume in your diet. What's so magical about fiber, you might wonder? "It’s a non-digestible carbohydrate that’s found in the world’s best, most nutritious foods — veggies, fruit, legumes, nuts, seeds, and 100% whole grains," London explained.

Having spent years working with clients with diabetes and heart disease in a private practice in New York, Zuckerbrot explains that she realized that eating more fiber helped people manage blood sugar levels and lower cholesterol — and promoted weight loss in the process. Besides appearing in a slew of good-for-you-foods, natural sources of fiber also fill you up so you're not feeling deprived later in the day. "These patients were simply feeling fuller throughout the day on fewer calories, which led to weight loss without hunger," Zuckerbrot said in an interview with Camille Styles.

The plan prescribes eating three fiber-filled meals and a snack each day, loading up on healthy carbs and lean protein, but also enjoying meals out and the occasional drink. In order to maintain long-term success, you're not supposed to eliminate food groups altogether, but you are asked to constrain the amount of carbohydrates you are eating in total. While the diet doesn't ask you to count calories outright, the careful consideration necessary for tracking servings on all sources of carbohydrates may be confusing to some, explains Stefani Sassos, MS, RD, CDN, a registered dietitian in the Good Housekeeping Institute. "Because you are counting carbs, you are also inadvertently counting calories in a way," Sassos explains, adding that each gram of carbohydrate carries 4 calories. "You are ultimately eating less calories because you're eating less carbs... But the restricted phases aren't meant to be permanent."

Sassos clarifies that the first phase of the F-Factor Diet is designed to last "approximately two weeks," according to Zuckerbrot's book, which also says that you may lose between 4 and 6 pounds at that point. You'll stagger carbohydrate-rich foods back into your diet gradually over the next two phases, and you're meant to remain on the third stage to maintain weight loss over time. You can get all the specifics in the book, but the plan includes three general phases:

1. Jumpstarting Weight Loss: Eat 35 grams of fiber and less than 35 grams of net carbs (3 servings) per day.
2. Continued Weight Loss: Aim for at least 35 grams of fiber and less than 75 grams of net carbs (6 servings) per day.
3. Maintenance Eating: Aim for at least 35 grams of fiber and less than 125 grams of net carbs (9 servings) per day.

How many grams of fiber should I eat on the F-Factor Diet?

At each stage of the F-Factor diet, you should aim to eat at least 35 grams of fiber per day. That's not an arbitrary number. The Dietary Guidelines for Americans recommends adults consume between 25-35 grams of fiber daily (6g of soluble fiber) depending on your age and gender. However, only a mere 5% of us of get close to that goal, according to a 2017 study published in the American Journal of Lifestyle Medicine.

Because the standard American diet tends to be lacking in fiber, Sassos explains that you shouldn't expect yourself to magically hit 35g of fiber consumption on your first day. "The American Institute for Cancer Research recommends 30g of fiber each day, and I support being somewhere in that 25-35g range for healthy adults through real whole foods," Sassos says, adding that it's no easy feat to eat your way through 35g of fiber overnight. "Increase fiber intake slowly and gradually, while simultaneously increasing your hydration to help fiber properly digest in your body."

What do you eat on the F-Factor Diet?

While the diet doesn't ask you to eliminate entire food groups outright, it does ask you to focus in on adding more fiber-full vegetables, fruits, beans, and whole grains to your plate. The first phase of the diet asks you to severely limit starches and starchy vegetables, most dairy, and fatty meats for the first two weeks of progress. After that, you should move on to Phase 2 and Phase 3, which doesn't place heavy restrictions on any foods — but you do need to hit that 35 grams of fiber benchmark, and you will still maintain a limit on total carbohydrate consumption.

You can get closer to consuming 35g of dietary fiber by loading up on these fiber-full foods, as listed by the Dietary Guidelines for Americans:

• Pulses: Beans, peas, chickpeas, lentils.
• Whole Grains: Bulgur, quinoa, barley, whole-grain bread, high-fiber cereal, shredded wheat cereal, bran cereal, rye crackers, whole-wheat pasta, air-popped popcorn.
• Fruits: Apples, pears, raspberries, blackberries, figs, oranges, bananas, guava, dates.
• Vegetables: Artichokes, avocado, collards, sweet potato, pumpkin, parsnips, squash.
• Nuts and Seeds: Pumpkin seeds, chia seeds, sunflower seeds, flax seeds, almonds, pistachios, pecans, hazelnuts, peanuts.

"Whether you’re opting in on F-Factor or not, choose foods that are in their most wholesome state as possible, within the confines of your budget and palate," London advised. "Oranges versus orange juice, roasted veggies versus veggie chips, and so on."

Does the F-Factor Diet really work?

The F-Factor diet may help you lose weight if that's your goal, and some of its tentpoles may also help you feel fuller throughout the day. In spite of the current controversy surrounding F-Factor's supplements and ready-to-eat products, its diet plan itself focuses on promoting wholesome foods rather than processed items, London said. "While it’ll work for weight loss, the tenants of the plan make it sustainable for anyone to make healthier choices because the program has you prioritizing real, whole foods that are nutrient-dense — without being a complete snooze," she added.

The bottom line: The F-Factor diet promotes eating more pulses, vegetables, whole grains, and fruit, a goal that most should strive for. However, it can be easy to get swept up in counting fiber intakes and carbohydrate limits, making it easy to lose sight of eating and enjoying your favorite foods in healthy moderation. "Prioritize wholesome, nourishing foods before re-thinking everything you eat in terms of the nutrients it contains," London said. "We benefit from nourishment from multiple sources and experiences — enjoying food should be front and center, not just focusing on one single nutrient!"