Fiber 101 - a podcast by Donna Psiaki Feldman MS RDN

Have you ever made a purchasing decision based on one of these food label claims?

Contains Fiber!

More fiber than [fill in the blank] !

Added Fiber!

With [fill in the blank] grams of fiber!

High Fiber!

You may have been played by a clever food marketer.

What exactly is fiber?  Fiber used to be defined as “roughage”, stuff that didn’t get digested, like those stringy bits in celery or the bran in whole wheat or corn kernels.  But the official official FDA definition of fiber includes all kinds of things that have no relationship to roughage:

“non-digestible soluble and insoluble carbohydrates (with 3 or more monomeric units), and lignin that are intrinsic and intact in plants; isolated or synthetic non-digestible carbohydrates (with 3 or more monomeric units) determined by FDA to have physiological effects that are beneficial to human health.”

No strings or roughage anywhere to be found.   Instead we get monomeric units, gums, gels and short-chain carbohydrates that are fermented by bacteria.  In short, anything that isn’t digested or absorbed by a human.   This definition gives the food industry incentive to identify non-digested/non-absorbed stuff that can be added to manufactured foods to boost the fiber content, including foods that never, ever had fiber in their natural state, such as yogurt.  Yogurt with added celery strings might be higher in fiber, but who would buy that?  But you can officially make your yogurt “high fiber” by adding inulin — a non-digestible carbohydrate that dissolves in liquid.  You can slap a High Fiber Health Halo on the yogurt and gain market advantage.  You can also add inulin or wheat dextrin to the mix for leaden energy bars or extruded cereals and make a high fiber claim on the label.

Why do we want more fiber?

Fiber has a great reputation.  It’s supposed to keep you regular, lower cholesterol, control blood sugar and make you feel full so you eat less, perhaps aiding weight loss efforts.  These’s some truth to those claims for some types of fiber, but not to all types of fiber.  Food marketers would prefer that consumers remain in the dark about those differences, and just believe that all fibers provide all benefits.  Precisely the kind of nutrition fakery I detest.  And I’m not alone.  I ran across an article recently that backed up my annoyance with specifics about what different fibers do and do not do.  It turns out, the best fibers for health benefits are the ones from whole foods.  No surprise there.

The article is chock full of details about how different fiber types are handled in the digestive tract.  Check out the article if you want the extreme details, such as the importance of viscosity, the gel-forming properties of carbohydrate chains and the fermentation of extracted fiber additives.  If you don’t have the time to wade through that, here are some of the key points:



* There are two basic classes of “fiber”: soluble and insoluble, which  refers to chemical properties of the fiber.

* Soluble fibers from intact foods (such as from oats or psyllium) hold water and are effective for lowering cholesterol or controlling blood sugar, thanks to their molecular structure.  Because these fibers are effective at holding on to water, they are effective stool softeners.

* Insoluble fibers, such as from wheat bran, do not impact cholesterol or blood sugar.  They can have a laxative effect due to direct irritation of the gut mucosa, which leads to secretion of mucous and water, promoting laxation.

* Research does not show any of these benefits from the extracted non-digestible fibers,

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