Intact Versus Functional Fiber

Steel cut oats or Fiber One? An in-depth look at the different types of fiber, and their effects on your health.

OneResult’s Carolyn Brown as already done an excellent job of detailing the benefits of dietary fiber so, without rehashing her flawless argument, I’ll get straight to the point: we need a lot of fiber in our diets, and most of us aren’t getting enough. Unfortunately, the simplicity ends there, as there are hundreds of different types of fibers, some of which occur naturally in foods and some that are isolated, extracted, or manmade. There are so many fibers, in fact, that in 2001 the Institute of Medicine published a 64-page report on the “proposed definition of dietary fiber.” Who knew fiber was such a complex beast?!

To summarize, the “dietary fiber” heading we see on the nutrition facts label is a combination of two fiber groups:

1. Intact Fibers: Technically, these are non-digestible carbohydrates and lignin that occur naturally in plants. Basically, this is what we think of when we hear the term “fiber.” Food sources include whole foods like fruits, vegetables, beans, nuts, seeds, and whole grains.

2. Added Fibers: These are non-digestible carbohydrates that have beneficial health effects in humans. These fibers are either synthetic, or extracted from plant sources and added to processed foods. They are also called “isolated,” or “functional” fibers, and you may find them added to traditionally low-fiber processed foods like orange juices, yogurts, granola bars, desserts, and certain cereals. They typically have funky names that will remind you of chem class.

Common Functional Fibers In Processed Foods: Chicory Root Extract, Inulin, Polydextrose, Maltodextrin, Resistant Starch, Hemicellulose, Cellulose, Methylcellulose, Fructooligosaccharides, Soluble Wheat Dextrin, Hydrolyzed Guar Gum, Tapioca Starch, Psyllium

So why is this important? There is a huge body of research supporting the benefits of intact fibers from fruits, vegetables, whole grains, etc. Consumption of fibers from these foods has been linked to improved laxation (i.e. less constipation), improved satiety, intestinal health, and decreased risk of obesity, cardiovascular disease, type 2 diabetes, and some cancers. How wonderful!

The case for functional fibers is not so strong. Because functional fibers are extracted, processed, and synthesized in so many different ways, it is incredibly difficult to summarize their health effects, and research varies widely across fiber type and dosage. Here’s how functional fibers stack up:

Improved Laxation: Studies have found conflicting results on use of functional fiber to improve stool consistency and frequency of bowel movements. Results vary with fiber type, dosage, and individual. One study, which compared use of a psyllium fiber supplement to dried prunes in a group of constipated adults, found dried prunes were significantly more effective in improving consistency of stools and increasing bowel movements per day, suggesting food sources of intact fiber may show better results. Gross, I know.

Improved Satiety: Again, studies have found conflicting results on use of functional fiber to increase feeling of “fullness” or satiety hormones. However, several studies in overweight and obese adults found people lost more weight and consumed less calories after eating functional fiber-fortified foods, versus low fiber alternatives. This could have potential implications for functional fiber as a tool for weight management.

Intestinal Health: There is a large body of evidence supporting the use of functional fiber as a prebiotic. For this reason, it’s often added to yogurts, basically as a food for your probiotics, which promote growth of good bacteria in your colon. There has been no direct link between functional fiber intake and decreased risk of colon cancer or inflammatory bowel disease.

Decreased Risk of Chronic Disease: There is compelling evidence that certain functional fibers may reduce risk of coronary heart disease by decreasing total and LDL (bad) cholesterol. Research is strongest for psyllium and oat and barley derivatives (beta-glucans). Studies have found inconclusive results on functional fiber consumption and improved insulin response and glucose levels after eating, and there is no evidence to suggest intake of functional fiber decreases risk of type 2 diabetes, obesity, or cancer.

Adverse Health Effects: There has yet to be any evidence of long-term adverse health effects in humans, but there also have not yet been any long-term studies on functional fiber. For now, adverse health outcomes are limited to mild-moderate gastrointestinal distress. The most common complaints are abdominal discomfort, flatulence, and in some cases, loose stools and diarrhea. Again, it’s important to note that most studies have looked at acute functional fiber intake, so the amount of functional fiber a person takes in over the course of a meal, a day, or a week. There haven’t been many studies that examine adverse health effects of consuming large amounts of various types of functional fibers over long periods of time.

The Take-Away? For now, functional fibers appear safe in small amounts. However, if you find yourself having unexplained stomach cramps or weird bowel movements, you may want to examine your ingredients labels a little more closely (ever had a Fiber One bar before a workout? Not pretty!)

If this is the case, look for whole grains or bran in the ingredient list to ensure minimal processing. In general, though the health benefits of these foods do not nearly equate to the benefits of fiber from natural sources, their potential benefits seem to outweigh the risks. So, if you need a bowl of high-fiber cereal or fiber-enriched yogurt to up your intake every once in a while, okay. But try to get most of your daily fiber intake from the good stuff. It’s suffice it to say a fiber-enriched Pop Tart will never have the health benefits of a good old-fashioned piece of fruit. But it will sure try!