Fiber: What's in a Name?

Just what is dietary fiber? Per St. Paul, MN–based AACC International’s 2001 “Report of the Dietary Fiber Definition Committee” to its Board of Directors: “Dietary fiber is the edible parts of plants or analogous carbohydrates that are resistant to digestion and absorption in the human small intestine with complete or partial fermentation in the large intestine. Dietary fiber includes polysaccharides, oligosaccharides, lignin and associated plant substances. Dietary fibers promote beneficial physiological effects, including laxation and/or blood cholesterol attenuation and/or blood glucose attenuation.”

Much debate went into that definition. Fiber has often vexed its definers because they’ve had to strike a balance between what fiber is nutritionally and where it shows up in chemical analysis. “While the physiologically based definitions most widely accepted have generally been accurate in defining the dietary fiber in foods,” says AACC on its website, “scientists and regulators have tended, in fact, to rely on analytical procedures as the definitional basis in fact.”

Even as the AACC definition acknowledges the plant-based dietary fibers that have historically been associated with physiological benefits, it also notes the non-digestible “analogous carbohydrates” that manufacturers extract from natural sources—or in some cases, synthesize—as ingredients for use in food.

Broadly classified as functional fiber, these don’t always show up in traditional analyses, although they’ve spawned a number of methods—like AOAC Methods 995.16 for β-glucan, 997.08 for fructans, 2002.02 for resistant starches RS2 and RS3, and 2000.11 for polydextrose—to detect them.

The name game doesn’t end there, though. Fibers are also generally considered either soluble (as in pectins, β-glucan, fructans, oligosaccharides, gums and some hemicelluloses found in legumes, oat bran, barley, vegetables and fruits) or insoluble (like most hemicelluloses, as well as the cellulose and lignin in whole grains, plant skins, and seeds). And that’s not to mention the in-between cases, like RS2, which qualifies as insoluble, but is prebiotic and fermented in the colon like soluble fiber.

Not your grandfather’s fiber

Nomenclature aside, a constellation of factors has aligned to benefit both fiber’s promoters and its fans—the latter of whose numbers are rising. “With growing consumer awareness of overall health and the importance of addressing health-related issues through diet, the world of fiber is changing,” says Wade Schmelzer, principle food scientist, Cargill Health & Nutrition, Minneapolis. “Consumer demand for fiber-containing products has escalated, opening the door to new application segments, such as dairy products, beverages and soups. However, consumers still expect the same great taste and texture from these products.”