I was eating Cocoa Pebbles recently for dinner (yes, I'm a bachelor) when I noticed something strange on the nutrition label. Cocoa Pebbles, according to the box, is a "good source of fiber." Who knew that I could get as many grams of fiber from Cocoa Pebbles as I could from a bowl of Cheerios or a slice of whole wheat bread? After a little research, I learned that higher doses of fiber are showing up in all sorts of bizarre places, like yogurts, cookies, brownies, ice creams, and diet drinks. Fiber, perhaps the only nutrient to be mocked in a Saturday Night Live parody commercial, is getting a makeover. And although we're eating more of it, it's not the same nutrient we've always known.
The fiber in Cocoa Pebbles comes from a little-known ingredient called polydextrose, which is synthesized from glucose and sorbitol, a low-calorie carbohydrate. Polydextrose is one of several newfangled fiber additives (including inulin and maltodextrin) showing up in dairy and baked-goods products that previously had little to no fiber. Recent FDA approvals have given manufacturers a green light to add polydextrose to a much broader range of products than previously permitted, allowing food companies to entice health-conscious consumers who normally crinkle their noses at high-fiber products due to the coarse and bitter taste of the old-fashioned roughage. These fiber additives serve dual purposes—they can serve as bulking agents to make reduced-calorie products taste better, such as the case with Breyers fat-free ice cream, and carry an added appeal to consumers by showing up as dietary fiber on food labels.
The problem with this is that nobody knows if these fiber additives possess the same health benefits as natural fiber found in whole grains, fruits, and vegetables. Fiber, which consists of nondigestible carbohydrates, was already one of the least understood nutrients even before the introduction of ingredients like polydextrose. Nutritionists and scientists have wrestled for years with how to define fiber and measure its health impact. It's a tricky thing to conduct a fiber study. (Consider for a moment the logistics of organizing a placebo-controlled, randomized, double-blind, fecal-mass study.) Even when it comes to the natural, wholesome stuff, like oats and kidney beans, nutritionists don't know for sure whether the health benefits derive from the fiber itself or from the collective impact of high-fiber foods.
The most recently accepted grouping by the Institute of Medicine divides fiber into two categories: dietary and functional. Dietary is the kind found naturally and intact in oat bran, whole wheat, beans, prunes, peas, and almonds, and other plants. Functional refers to both the synthetic variety like polydextrose as well as naturally occurring inulin, which is extracted and purified from chicory roots.
Polydextrose shares with dietary fiber one fundamental property: It seems to rev up your GI tract. It does so, however, at a fraction of the level of wheat bran. And while diets heavy in oat bran have been shown to lower cholesterol levels and whole grains have been linked to lower risks of heart disease, there's no evidence that polydextrose protects cardiovascular health. A spokeswoman for Danisco, a leading producer of polydextrose, says it promotes digestive health but added: "Of course, it is harder to prove without doubt the health benefits of adding a single ingredient to the diet, than it is to prove the benefits of consuming natural fibers in fruits." Studies on animals have shown that inulin has a pre-biotic effect by altering intestinal microflora, but the "potential beneficial effects in humans are not well understood," according to a 2005 report by the IOM.