Q&A: Is Added Fiber Beneficial?

Q: I’m trying to follow a high-fiber diet and wondered if foods with added fiber have the same benefits as foods naturally high in fiber?

A: As with most nutrition questions, the answer is: it depends.

Fiber is a plant form of carbohydrate that our body’s digestive enzymes can’t break down.  Since we can’t break it down, we can’t extract any energy from it, which means fiber has no calories by definition. But just because we can’t digest it, that doesn’t mean the friendly bacteria in our intestines can’t: some forms of fiber (called “prebiotic” fiber) can serve as food for these bacteria. Fiber actually helps promote a healthy population of beneficial gut bacteria.  Furthermore, although we can’t get energy from it, we can still benefit from it in other ways. “Soluble” forms of fiber form a gel-like, spongy texture as they slowly move through our digestive tract, keeping us feeling fuller for longer and mopping up excess cholesterol and toxic substances in the process. “Insoluble” forms of fiber add bulk to our stool and help prevent constipation. Various plant-based foods contain a combination of all these types of fiber.

The Institute of Medicine recommends that women aim to eat 25g of fiber per day, and men consume 38g per day. At a minimum, aim for 14g of fiber for every 1,000 calories in your diet. On average, Americans only eat between 10-15g of fiber per day–and Americans on low-carb diets may eat even less.

Virtually all of the scientific research to date on the benefits of a high-fiber diet–which include lowering cholesterol, preventing constipation, reducing risk of diabetes and heart disease, improving blood sugar control in diabetics, and maintaining a healthy weight– has looked at diets rich in natural, whole-foods based sources of fiber, such as whole grains, fruits, vegetables, beans and nuts. In most cases, the type of fiber that naturally exists in these foods differs from the isolated, more processed forms of fiber that many manufacturers are adding to foods like cereal, bread, energy bars, yogurts and baked goods to boost the number of fiber grams they can claim on the label. Therefore, we can’t automatically extrapolate that a diet rich in these newer, fiber-enriched, “functional foods” will have the same health benefits as a diet rich in the types of high-fiber foods that researchers have investigated for years.

That doesn’t mean you won’t get any benefit from these so-called “functional fibers,” though. Certain fiber supplements, such as those made from psyllium husk (e.g., Metamucil®), will indeed help with constipation and cholesterol-lowering; they may also have a modest effect on weight management and blood sugar management in diabetes. Inulin (aka “chicory root extract”) is a known prebiotic that should help nourish the healthy bacteria in your gut and promote regularity. But its possible effect on disease risk reduction is still unknown. An isolated fiber ingredient called “maltodextrin,” conversely, is less likely to have an effect on digestive regularity or disease prevention, though more research is needed.

My recommendation is that if you’re looking to achieve the maximum benefits from a high fiber diet, aim to get most of your fiber from whole foods. Include fruits, vegetables, beans and nuts in your daily diet, and look for whole grains (e.g., whole wheat, whole oats, brown rice, barley, quinoa), whole grain flours and bran (wheat bran, oat bran, rice bran) high up on the ingredient lists of breads, cereals and bars.  You can also add dried fruits, ground flaxseeds or chia seeds to cereals, yogurts, smoothies and baked goods to boost their fiber content.  Processed foods with added fiber certainly won’t hurt you and may provide some limited benefits, but I wouldn’t rely on them as the primary source of fiber in your diet.


Tamara Duker Freuman, R.D.

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