Is the F-Factor Diet just another one of the latest diet fads? Or is this high-fiber eating plan actually legit?

By Karla Walsh
June 30, 2019
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high-fiber food
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Registered dietitian Tanya Zuckerbrot calls fiber the "miracle carb." She loves it so much, in fact, she designed an entire diet around it. Since 2007, fans have been following her bible The F-Factor Diet, and Zuckerbrot claims the average F-Factor dieter sheds 8 to 10 pounds in the first month—without hunger or feelings of deprivation. And it's making waves again after a new research review published in The Lancet found that those who eat more fiber (between 25 to 29 grams per day) reduce their risk of dying from cardiovascular disease by 15 to 30 percent, compared to those who eat about 20 grams or less per day. (See: This Study On Carbs Might Make You Rethink Your Keto Diet Aspirations)

So is Zuckerbrot full of it—or has she finally found a weight loss solution for those who don't want to count calories or kick it in ketosis on the keto diet?

What Is the F-Factor Diet, Exactly?

"The F-Factor Diet is a lifestyle that focuses on consuming high-fiber carbohydrates combined with protein at every meal to keep you satisfied and allow you to lose weight while consuming fewer calories," explains Lauren Harris-Pincus, M.S., R.D.N., founder of and author of The Protein-Packed Breakfast Club. "Plus, aside from weight loss, the health benefits of fiber such as improved cholesterol, blood sugar, regularity, and sustained energy levels are a side bonus."

About 95 percent of Americans don't come close to hitting the amount of daily fiber recommended by the U.S. Dietary Guidelines, says Harris-Pincus, which is 14 grams per 1,000 calories or approximately 25 grams for women and 38 grams for men each day. The F-Factor promotes aiming for a minimum of 35 grams daily and tracking them via a food journal to keep yourself accountable. Zuckerbrot even shares an example journal and additional tips on her website, and she recommends three meals and one snack per day.

There's zero promotion of exercise on the F-Factor diet. In fact, Zuckerbrot suggests avoiding cardio, in particular, saying that it increases your appetite so much that you'll end up eating more calories than you burn.

What Can You Eat On the F-Factor Diet?

The F-Factor diet focuses on "net carbs". Since carbs from fiber aren't digestible, "you subtract the fiber content from the total carbohydrate on the label to arrive at 'net carbs', meaning the grams of carbs that are available for digestion by the body," says Harris-Pincus. (BTW, here's exactly how many carbs you should eat a day.)

F-Factor dieters follow several phases and increase total net carb consumption as they inch closer to their goal.

Phase 1: Less than 35 grams net carbs per day, or about three servings

Phase 2: Less than 75 grams net carbs per day, or about six servings

Maintenance Phase: Less than 125 grams net carbs per day, or about nine servings

Low-net carb foods Zuckerbrot recommends while on the F-Factor diet:

Beans and legumes of all varieties


High-fiber vegetables such as beets, broccoli, carrots, cauliflower, and sweet potatoes

High-fiber fruits including apples, berries, oranges, and pears

High-fiber cereals

She also sells F-Factor protein powder and bars for additional on-the-go options. Alcohol (wine, spirits with calorie-free mixers) is permitted, as long as consumption is in moderation and within your daily net carb limits. (Related: Your Guide to Drinking Alcohol On the Keto Diet)

"It's surprisingly easy to follow when dining out and traveling with a few simple substitutions," says Harris-Pincus.

Is the F-Factor Diet Healthy?

Now that we've covered the basics, here are the nutrition facts about the F-Factor Diet, straight from Harris-Pincus and Kris Sollid, R.D., senior director of nutrition communications for the International Food Information Council (IFIC) Foundation in Washington, D.C.

1. Fiber IS great for you.

Simply put, Americans consume way too many refined grains and high sugar foods that do not provide adequate nutrients and fiber, says Harris-Pincus.

"Foods that are high in fiber are healthy, nutrient-dense foods like fruits, veggies, nuts, beans, seeds, and whole grains," she says. "You should be eating these plant-based foods as the majority of your daily intake—in addition to lean proteins. They contain essential nutrients such as vitamins, minerals, antioxidants, and phytochemicals."

All of those factors mean that "fiber helps to reduce the risk of cardiovascular disease by lowering blood cholesterol, reducing blood pressure, decreasing inflammation," says Sollid. It's also been linked to lower the risk of many cancers.

It also adjusts the rate at which your digestive system processes foods, making you more regular and boosting the health of your gut microbiota, adds Sollid. (Related: Is the Microbiome Diet the Best Way to Promote Gut Health?)

"Fiber-rich foods also tend to provide more volume than lower-fiber foods, which is thought to generate a greater feeling of fullness in fewer calories," she says. "Additionally, high-fiber foods will require you to chew more. This simple action means it takes longer to eat, which could also lead to eating fewer calories overall." (Related: These Health Benefits of Fiber Make It the Most Important Nutrient In Your Diet)

2. But be aware: you can consume too much fiber.

All that being said, "you can overdo it with fiber, so try to increase your fiber intake gradually over time and drink plenty of fluids while doing so," says Sollid. "Too much too quickly, and not drinking ample fluids during the F-Factor diet—or any high-fiber diet—can contribute to nausea or constipation." (Learn more about what can happen when you eat too much fiber.)

3. There's not just one kind of fiber.

Technically, "net carbs" don't have a legal definition, and the term isn't accepted by the Food and Drug Administration (FDA) or the American Diabetes Association, says Harris-Pincus.

However, the difference between soluble and insoluble fiber is defined by the FDA:

"Soluble fiber dissolves in water to form a thick gel-like substance in the stomach. It is broken down by bacteria in the large intestine and provides some calories."

"Insoluble fiber does not dissolve in water and passes through the gastrointestinal tract relatively intact and, therefore, is not a source of calories."

Since some fibers are partially-digestible and provide a couple of calories per gram, Harris-Pincus recommends that individuals with Type 1 diabetes who are following the F-Factor diet (or any diet plan) should be supervised by a registered dietitian or doctor. (Related: Can the Keto Diet Help with Type 2 Diabetes?)

4. You still need to be "calorie aware" on the F-Factor diet.

You count and track carbs and fiber on the F-Factor diet, but it's still important to be calorie aware (no need to be a calorie counter!), says Harris-Pincus. (Related: Counting Calories Helped Me Lose Weight—But Then I Developed an Eating Disorder)

"The more fiber you consume from nutrient-dense foods, the more satisfied you are," she says.

Still, you can easily fall victim to consuming on more calories than you might think.

"Often people believe that they are consuming 'healthy' food, but the portions are too large given then calorie content such as avocados or nuts," says Harris-Pincus. "I always recommend measuring those higher-fat and higher-calorie items when trying to lose weight on any diet."

Bottom Line: The F-Factor Diet may be beneficial for weight-loss if you're looking for a diet plan that doesn't require counting calories. Still, fiber can help you sneakily fill up.

"Ultimately, the number of calories you consume will determine how your weight changes," says Sollid. "But fiber can play a role in that. Many high-fiber foods are also low in calories, like vegetables, and eating a variety of fiber-rich foods can help keep you feeling satisfied by delivering a larger volume of food to help keep you feeling full with fewer calories."

Just don't forget to add another important "F" to this plan to keep your muscles strong and your heart healthy: fitness.