Fiber, Fiber Everywhere and What Are We to Think?

Fiber is everywhere these days. You can't walk down a supermarket aisle without "High Fiber!", "Improves digestion!" or "100% MDR of Fiber!" shouting at you from every shelf. And its no longer just cereals either. Yogurt, ice cream, bread, pastries, cookies and even candy now all boast about their fiber content. Is it fact? Or food industry fiction?

What is fiber anyway? And why does it matter?

"Fiber is a group of indigestible carbohydrates than are not broken down - digested - in the stomach or small intestine," says Nicola McKeown, a nutrition scientist at Tufts University near Boston. Among its many health benefits adequate fiber improves digestion, lowers cholesterol and blood pressure, helps regulate fluctuations in blood sugar and helps us loose weight. The recommended daily fiber intake is 38g for men and 25g for women. The typical American gets about 15g per day. Supplements and fiber added to foods seem like a good way to close the gap. But are they?

A 2002 National Academy of Sciences study grouped nutritional fiber into two broad categories: Intact and Processed. Intact fiber is that found in fruits, whole grains, vegetables and plants. Processed fiber is extracted from plants or formulated in a laboratory. Under current labeling rules, either type of fiber is listed as just "fiber".

Not all fiber is alike, nor does all fiber have the same health benefits. "They (fibers) don't all do the same thing," explains McKeown, "any more than all vitamins or minerals do the same thing."

With intact fibers this is generally not an issue because fruits, beans, whole grains and vegetables all contain a mixture of different fibers. With processed fibers that is not the case. "Some may have no health benefits at all," says McKeown. "Food producers add fiber for a variety of reasons, and that sometimes gives the food a health halo."

A more useful breakdown of fibers is insoluble, soluble, viscous and fermentable.

Insoluble fiber does not dissolve in water, and it isn't broken down by the gut and absorbed into the bloodstream. It adds bulk to waste in the digestive system, which helps keep you regular and prevent constipation (as well as any related problems, like hemorrhoids).

Soluble fiber, on the other hand, will dissolve in water and so can enter the bloodstream.  It helps control blood sugar and lower cholesterol.

Viscous fiber absorbs water to form a gel-like substance inside the digestive system. It helps soften stool so it can slide through the GI tract more easily and it also binds to substances like cholesterol and sugar, preventing or slowing their absorption into the blood. It may also boost the population of good bacteria in the gut, which is linked to improved immunity and anti-inflammatory effects.

Fermentable fiber is broken down by bacteria in the large intestine. (Think gas.) This promotes the growth of beneficial bacteria in the gut, aids in the absorption of certain minerals and lowers acidity.

Most processed fibers are soluble, non-viscous and fermentable. As such they are the least likely to provide any significant health benefits.

So where does this leave the person who just wants to eat a healthy diet? Health experts set dietary fiber targets assuming the consumption of fiber-rich fruits, vegetables and whole grains that all contain a mix of different fibers, not on cookies and candy to which a single processed fiber may have been added as an afterthought.

So your first line of defense is to get enough dietary fiber from various plant sources. If you do choose to supplement (I do) make sure you know what you are getting. If the label makes it confusing, difficult or impossible to figure it out, be suspicious and try something else.