The F-Factor Diet isn't new: Zuckerbrot, who has worked high-profile clients like Megyn Kelly and Katie Couric, and is the official dietitian to the Miss Universe Organization, per the Times, published her book, The F-factor Diet: Discover the Secret to Permanent Weight Loss, in 2006.The F-Factor Diet, in the broadest of terms, is a high-fiber diet for men and women (the "F" stands for fiber, according to the diet's website). The reasoning here, is that "fiber has zero calories-so you get to fill up, without filling out," the website says.First, a quick reminder about what fiber is: "There are two types of fiber," Shana Minei Spence, MS, RDN, a dietitian based in New York City, tells Health. "There's soluble fiber, [which] dissolves in water to form a gel-like material and is said to help lower blood cholesterol and glucose levels." Soluble fiber is found in oats, peas, beans, apples, citrus fruits, carrots, barley and psyllium. Then there's insoluble fiber, which promotes bowel movements and can bulk up your stool, Spence says. It's great for constipation or irregular stools, and can be found in whole-wheat flour, wheat bran, nuts, beans, and fibrous vegetables. Since your digestive system can't break down fiber into energy, it also helps make you feel full.The F-Factor Diet encourages followers to track fiber and net carbs, but also has recommendations for additional grams of fats you can have each day, as well as ounces of protein you should have at each meal, plus a snack. That equates to about 10 and 14 ounces of lean protein per day for women, about 90-126 grams-which is significantly above the amount recommended by the World Health Organization, which suggests 0.8 grams per kilogram of bodyweight (for a 150-pound woman, that's 55 grams a day).It's also important to note that, while the diet says it doesn't limit the number of a dieter's calories per day, the recommendations for other foods ultimately limits overall calorie intake, providing a built-in "calorie cap," according to the F-Factor book. Each step, outlined below, also has its own cap on calories.