The F-Factor Diet Promises the "Secret to Permanent Weight Loss," But Is It Legit? (2024)

  • The F-Factor Diet is based on the idea that taking in more fiber will slim you down and keep you lean.
  • The F-Factor asks you to eat even more than the recommended amount of fiber for women—35 grams—mostly in the form of all the healthy, fiber-rich foods.
  • Experts say the F-Factor diet can help you lose weight, but that if you don’t want to have to depend on processed high fiber bars or powders, this isn’t the right plan for you.

You probably first heard about fiber from your grandma, who, in a quest to stay “regular” stirs what looks like pencil shavings into her morning OJ. Not appealing.

You’ll be relieved to know that the F-Factor Diet—F is for fiber, kids!—is about more than keeping things moving (and does not require you to sip sludgy liquid). New York City dietitian Tanya Zuckerbrot’s eating plan (which actually came out more than a decade ago) is based on the idea that taking in more fiber, what she calls the “miracle carb,” will slim you down and keep you lean.

The idea does have scientific heft. “Fiber is a micronutrient that fills us up quickly and keeps us feeling full and satisfied for long periods of time. This fullness helps to keep us from unnecessary snacking, and that can help boost weight loss,” says Brigitte Zeitlin, M.Ph., R.D., a nutritionist in New York City.

Weight loss potential aside, eating enough of it (something the vast majority of us do not do) is just plain good for you. A major report in the journal Lancet observed that the highest consumers of fiber showed a 15-30% decrease in mortality from a bunch of causes, including cardiovascular conditions, stroke, diabetes and colorectal cancer, compared to those who ate the least.

That does sound potentially miraculous, but like any weight loss regimen, whether it’ll work for you is highly individual. Here’s what you need to know about the F-Factor and how to determine it’s your forever food plan.

So, what is fiber in the first place?

Fiber, a nutrient in plants that you can’t digest or absorb, comes in two forms, soluble fiber and insoluble fiber.

Simply put, soluble fiber pulls in water and forms a kind of goopy gel, which slows digestion. Look for it in beans and nuts, oat bran and barley, lentils, peas and some fruits and veggies. It’s also in psyllium husk powder, most likely what grandma spikes her OJ with.

Insoluble is found in wheat bran, veggies and fruits and adds bulk to your poop so it collects waste as it moves through your GI tract.

You’ve probably noticed that Devil Dogs and Sour Patch Kids aren’t listed here as good sources of fiber. That’s because they’re not. The Academy of Nutrition and Dietetics wants women to eat around 25 grams a day (guys need 38), something only 5% of us do, in part thanks to all the processed foods and refined carbs Americans eat.

Gotcha. So what is the F-Factor Diet, exactly?

The F-Factor asks you to eat even more than the recommended amount of fiber for women—35 grams—mostly in the form of all the healthy, fiber-rich foods mentioned above. It also includes lean proteins, and (after the initial phase-in period) discourages the deprivation that derails so many dieters’ dreams. “Our approach doesn’t trick your body or shock the system into a state of semi-starvation. It’s actually about routine maintenance: giving your body what it requires to function the way it is supposed to,” the website says.

There are three phases of the F-Factor:

Step 1: For two weeks, you eat fewer than 35 grams of net carbs a day (the term “net carbs” refers the number of grams of carbohydrate, minus the number of grams of fiber you eat.) This is to jumpstart weight loss, make you more aware of your eating habits, and gradually increase your fiber intake, according to the book. During this phase, you skip starchy carbs, go easy on the fruit, avoid dairy and make sure your proteins are super lean.

Step 2: In this phase, you eat 75 net carbs daily, which gives you more flexibility. You can even have some alcohol.

Step 3: In the maintenance phase, you can eat about 125 grams of net carbs.

The book guides you through how to figure out net carbs, which foods are better choices, offers recipes as well as tips to stay on track and make the diet work for you until you reach your goals.

Zuckerbrot, Tanya The F-Factor Diet: Discover the Secret to Permanent Weight Loss

The F-Factor Diet Promises the "Secret to Permanent Weight Loss," But Is It Legit? (1)

Zuckerbrot, Tanya The F-Factor Diet: Discover the Secret to Permanent Weight Loss

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Ah, but is the F-Factor Diet healthy?

Yes, if you do the right way. “I think the foundation on the F-Factor diet is good, eat more fiber. That’s great, because again, that means eat more vegetables, whole grains, fruits, legumes—all healthy foods that contribute to weight loss, lower risk of heart disease, diabetes, inflammation, and promote a healthy GI tract,” says Zeitlin. “It also focuses on lean proteins, which is another pro in my book.”

Zeitlin also likes F-Factor for what you won’t be eating much of. “Filling up on these fiber-rich foods leaves less room for white bread or starch products, that typically contribute to weight gain,” she says. You’re also likely avoiding sugar if you forgo packaged foods.

Still, there are some potential issues, says Lauren Slayton, R.D. M.S., co-founder of Foodtrainers, a nutrition practice in New York City. The diet includes supplemental fiber products, such as high fiber cereals and crackers, which she says are not optimal. “Fruits and vegetables naturally have fiber “packaged” with water,” says Slayton. “Fiber products do not. You need water to move fiber through your intestines. We have had clients who reported bowel obstructions and impaction, before coming to us, from overdoing supplemental fiber products.” Fiber from whole foods is awesome, fiber from products, however, isn’t so hot.

More ick: Slayton says you can become reliant on mega-fiber products. “Once your intestines get accustomed to being bulldozed (or “bran-dozed”) they kind of get used to it,” she says. “Pull fiber crackers and supplements from someone’s diet and they suddenly cannot “go”, even if they weren’t previously prone to constipation.” It’s fine to use a fiber supplement occasionally, she says. “But if your day is filled with fiber powders, bars, crackers etc., you might want rethink things.” Got that, grandma?

And if you're starting from low fiber, ramping up your intake as F-Factor recommends in Step 1 “Can be, um, unpleasant for your colleagues, friends and family, not to mention you,” says Jaclyn London, M.S., R.D., author of Dressing on the Side. She’s talking of course about gas, bloating and spending half your day in the bathroom. London says the basics of the plan are great, but she’d counsel that some people need to build up daily fiber grams more gradually, so "F" doesn't stand for flatulent.

Hmm. Are the claims of F-Factor Diet overblown?

The F-Factor’s website is correct when it says that fiber makes losing weight easier because it adds bulk to foods, slows digestion and satisfies hunger.

But it also has a few potentially misleading claims, says Zeitlin. For one, it says that fiber “absorbs calories.”

Does it? The answer is yes—and no. “Vegetables are very high in fiber and very low in calories, so if you are bulking up on your veggies for fiber, you are naturally “absorbing” fewer calories because the food itself is lower in calories,” explains Zeitlin. “And yes, our bodies cannot digest or absorb parts of dietary fiber that we take in from fruits, veggies, and whole grains, so you are absorbing less calories of those foods.”

But there are no miracle food combos that’ll cancel out calories, she says. “If you are pairing that fiber with ice cream—say topping your ice cream off with some berries—you are still absorbing all the calories from the ice cream,” she says. “It doesn’t magically lower the amount of calories per meal you are taking in total from the meal.”

It also says that fiber “boosts metabolism.” “The human body can’t digest fiber, but it attempts to, burning calories in the process,” it says.

Does it? Zuckerbrot cites this study, which found that subbing whole grains for refined grains (thus upping fiber) increases calorie burn. London, however, points out that any calories your body burns up processing the food you eat is a tiny proportion of your overall metabolic rate, and depending on the caloric content of the high-fiber foods you eat, you could offset that boost.

The upshot is, fiber is a total yes, and most of us could use a lot more of it, but it isn’t a major fast-forward for your metabolism. “Factors that do help boost your metabolism are working out or staying physically active, eating at regular times throughout the day (like every 3-4 hours), drinking water, getting enough sleep, and increasing your muscle mass,” says Zeitlin. Fibrous foods do tend to contain vitamin B, which can help contribute to a healthy metabolism, she says. “But it is the B vitamins that do the work.”

How to Win on the F-Factor Diet

So you want to give it a go! Have at it, keeping these tips in mind:

Drink a ton of water.

“Taking in more fiber without water can leave you feeling constipated, the exact opposite of what you want,” says Zeitlin. “So make sure you double up your water intake to make sure you don’t get bloated and uncomfortable.”

Listen to your body.

“Everyone is different, so pay attention to which high fiber foods feel good for you and which do not. Bloat and gas are signs that something is off, either those Brussels sprouts don’t work for you or you are not drinking enough water,” says Zeitlin.

Keep a journal.

Doing so will not only help you track your fiber and net carb intake, but doing so has been shown in other research to aid in losing weight.

Bottom line: F-Factor can help you lose weight for sure. So can any other diet that you like enough to stick with long term. Ask yourself, “Is this a long-term sustainable option for you? If it is, and you feel great, then great! You do you!” says Zeitlin. “But if you don’t want to have to depend on processed high fiber bars or powders, then this isn’t the right plan for you. You can keep what you like about it and adapt it to what feels more realistic for you long term. If you focus on eating more veggies at each meal, you’ll get to where you want to be.”

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The F-Factor Diet Promises the "Secret to Permanent Weight Loss," But Is It Legit? (2)

Stephanie Dolgoff

Health Newsroom Director

Stephanie (she/her) is the director of the Hearst Health Newsroom, where she writes, edits and oversees all health content for Good Housekeeping, Prevention and other Hearst titles. She has covered women's physical and emotional health, nutrition, sexuality and the multitudes of topics they contain for national publications for decades, and she is also a bestselling author, a mom of twins, a dog mom and an intuitive eater in progress.

The F-Factor Diet Promises the "Secret to Permanent Weight Loss," But Is It Legit? (2024)
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