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Dear Dietitian – What are the best fiber sources?

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PICT Leanne McCrate Dear Dietitian
Leanne McCrate, RDN, LD

Dear Dietitian,

I am health conscious and try to get enough fiber in my diet, but sometimes I miss the mark. I noticed some protein bars have 10 grams of fiber. Are these good for you?


Dear Jim,

The Dietary Guidelines recommend Americans consume 25 to 30 grams of fiber per day. Fiber is defined as an indigestible carbohydrate, which means the human body cannot break it down, and it passes through the digestive system unchanged. Fiber is found naturally in plant foods and exists in two forms, soluble and insoluble. Soluble fiber is found in oats, apples, nuts, flaxseeds, and beans, to name a few. Insoluble fiber is found in wheat bran, barley, broccoli, dark green leafy vegetables, and root vegetable skins.

Health benefits of a high-fiber diet include rates of obesity, type 2 diabetes, heart disease, and some types of cancer. Most Americans fall dismally short of reaching the recommended dietary fiber intake, with an average consumption of about 15 grams daily. Food manufacturers have added fiber to yogurt, protein bars, beverages, and cookies. To distinguish this type from naturally-occurring fibers, they are referred to as added fiber, functional, synthetic, or isolated fiber. They can be extracted from foods naturally containing fiber or produced in a lab. 

The Food and Drug Administration (FDA) proposed a regulatory definition of dietary fiber to protect consumers. It requires food manufacturers to present scientific evidence on the health benefits of added fibers. They must have at least one of the following physiological benefits: lowers blood glucose, lowers cholesterol levels, lowers blood pressure, increases the frequency of bowel movements, increases mineral absorption in the intestinal tract, or reduces caloric intake (1).

Some added fibers that met the FDA requirements are beta-glucan soluble fiber, psyllium husk, cellulose, guar gum, pectin, and locust bean gum. Based on a scientific review, the FDA plans to add the following to the functional fibers list: mixed plant cell wall fibers, inulin (chicory root), high amylose starch, polydextrose, resistant maltodextrin/dextrin, and others (2). These ingredients must be listed on the nutrition label.

Dear Dietitian recommends getting most of your fiber in whole foods for two reasons. First, the research on fiber and disease prevention has been conducted on whole foods like fruits, vegetables, and whole grains. Fiber isn’t isolated in the research process. Second is what I like to call the x-factor, which could be something research has not yet discovered. For example, it could be a particular nutrient plus fiber that together has a protective benefit. That said, supplementing your fiber intake with functional fiber is an acceptable strategy.

Until next time, be healthy!

Dear Dietitian


1-2.  Questions and answers on dietary fiber (January 10, 2020) Retrieved from

Leanne McCrate, RDN, LD, is an award-winning dietitian nutritionist based in Missouri. Her mission is to educate consumers on sound, scientifically-based nutrition. Do you have a nutrition question? Email her at Dear Dietitian does not endorse any products, health programs, or diet plans.