If there’s one message you hear a lot these days, it’s about the importance of getting dietary fiber. Research shows most people fall short of meeting their fiber requirements. In fact, the average person gets about half the currently recommended amount of 25 grams per day for women and 38 grams for men. In fact, a 2013 consumer survey conducted by the International Food Information Council found only 5% of respondents get enough dietary fiber.
What’s the big deal about fiber? Not only does this non-digestible form of carbohydrate help keep you “regular,” getting more of it may lower your risk for type 2 diabetes and heart disease, based on a number of studies. Unfortunately, processed foods, which comprise the bulk of the American diet, usually lacks sufficient fiber.
Two Types of Fiber: The Soluble Form
Fiber refers to carbohydrates that digestive enzymes can’t break down. As a result, you don’t absorb it. Dietary fiber comes in two forms: soluble fiber and insoluble fiber. Soluble fiber is the type that has the most health benefits to support it. When you eat a food rich in soluble fiber, some types form a gelatinous glob in your digestive tract. Once in your gut, this jelly-like substance slows down the absorption of sugars, so you get less of a post-meal glucose spike. This type of fiber also delays the absorption of fats.
The absorption delay you get when you consume soluble fiber also helps you feel fuller when eating a meal. A number of studies show diets high in fiber aid in weight loss, although it’s not clear whether it’s due to the fiber itself or the fact that fiber displaces other higher calorie foods.
Soluble fiber is the form linked with a lower risk for heart disease, partially because it slightly lowers LDL-cholesterol when you consume it in sufficient amounts. Another way soluble fiber may reduce the risk of cardiovascular disease is by lowering the blood sugar response to a meal and by boosting insulin sensitivity.
You may not be able to break down and absorb fiber, but bacteria in your small intestines can. When you eat fiber, gut bacteria break down some types of soluble fiber into short-chain fatty acids, butyrate, and acetate, which aid in the absorption of minerals like calcium and help keep the lining of your colon healthy. Fiber is an important food source for gut-friendly probiotic bacteria that help support digestive health and prime your immune system. Surprisingly, your gut and the bacteria that live there is home to more than 70% of your immune system.
Insoluble Fiber
The other type, insoluble fiber, won’t do a lot to lower your risk for heart disease or diabetes, but it does increase the size of your stool and speeds up the movement of food and waste through your intestinal tract. As such, it’s a good antidote for constipation and for staying regular.
Enter Functional Fiber
Food manufacturers, in an effort to get in on the action, have developed a number of “functional fibers.” Functional fiber is fiber isolated from foods, extracted from foods or synthetically made in a lab, unlike natural fiber that’s still structurally attached to the plant. It also includes natural plant-based fiber that’s modified in some way.
Examples of functional fibers: pectin, cellulose, b-glucan, polydextrose, resistant starch, guar gum, dextrins, and inulin. You may have seen functional fibers listed as ingredients on packaged food labels. Food manufacturers love functional fibers because they can add them to processed foods to inexpensively increase the fiber content.
Like natural dietary fiber, functional fiber is non-digestible, but studies specifically looking at its effects on disease risk, unlike natural dietary fiber, are lacking. Plus, when you consume fiber in a functional form, more often than not, you’re getting it from processed foods that are inherently less healthy than foods you consume in their whole, natural state.
Think of the additional “perks” you get when you bite into a naturally fiber-rich piece of fruit or vegetable – anti-inflammatory phytochemicals and natural vitamins, minerals and antioxidants. Plus, a number of people experience digestive upset and bloating when they consume lots of functional fiber. No doubt, some functional forms of fiber have potential. Gut bacteria can break down functional fiber just as they can natural fiber, and functional fiber makes foods more filling.
Viscous and Fermentable Dietary Fiber
Just as important as whether a fiber is soluble or insoluble is how “viscous” and “fermentable” it is. Viscous refers to viscosity, or how effectively a fiber component forms a thick gel in the intestinal tract while fermentable denotes how well gut bacteria break fiber down into gut-healthy short-chain fatty acids. In fact, the Institute of Medicine now recommends that fiber be classified as viscous or non-viscous, fermentable or non-fermentable, rather than “soluble” or “insoluble.”
Viscous and fermentable fiber offers the greatest benefits for blood sugar, cholesterol, and gut health. Research suggests it’s the type that’s most satiating too. Examples of viscous fiber include pectin, found in citrus fruit and the skins of apples, beta-glucan in oat bran, flaxseed, guar gum, and psyllium.
The Bottom Line
The best way to meet your body’s need for fiber is to enjoy vegetables, legumes, oats, fruits, whole grains, nuts and seeds, and fiber in their natural, unprocessed state. In terms of health, it’s better to get fiber in a functional form than to get no fiber at all, but the best way to meet your body’s fiber requirements is to eat foods that are naturally rich in fiber and provide other vitamins and minerals your body needs for optimal health.
Although it’s important to get the recommended amount of fiber daily, don’t rapidly increase the amount of fiber in your diet or you may experience unpleasant symptoms like bloating and gas. Slowly boost the quantity of fiber you take in over several weeks. You may also discover you tolerate some fiber-rich foods better than others. Experiment a bit and find out which ones help you meet your fiber needs with the least amount of flatulence.
References:
American Family Physician. Volume 91, No. 9. May 1, 2015.
USDA. “Dietary Functional and Total Fiber”
Today’s Dietician. Volume 15. No. 12, page 32. December 2013.
Medline Plus. “Dietary Fiber”
Nutraceuticals World. “Fiber as a Functional Food”
Crit Rev Food Sci Nutr. 2006;46(8):649-63.
Obes Rev. 2011 Sep;12(9):724-39. doi: 10.1111/j.1467-789X.2011.00895.x. Epub 2011 Jun 16.
J. Nutr. February 1, 2000 vol. 130 no. 2 272S-275S.
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