How to Diet: Is Adding Processed Fiber to Foods Beneficial?

Experts advise us to eat more fruits, vegetables, beans, whole grains, fish, and nuts. Instead, our stores are stocked with junk foods that claim to deliver those same foods. “It’s about marketing,” says Marion Nestle of New York University. “It’s not about health.”

Take fiber, for example:

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“Most consumers’ diets are fibre deficient—containing less than half the recommended daily amount of fibre,” explains DuPont’s brochure for its Litesse (“the Better Fibre”). “Tap into this market opportunity and project a healthier image for your product…”

Litesse is polydextrose, an odorless white powder made by connecting chains of glucose (dextrose) with bonds that are not easily broken apart by our digestive enzymes. So foods that replace sugar or fat with polydextrose have fewer calories…and, technically, more fiber.

It’s not just DuPont. “Who knew fiber could be clean and clear?” asks one of Archer Daniels Midland’s brochures. “Use Fibersol-2 digestion resistant maltodextrin in your beverage products and consumers will start looking at fiber in a whole new way!”

Indeed.

Why bother with a bowl of whole-grain cereal when you can have a Kellogg’s To Go Milk Chocolate Breakfast Shake, with “5 grams of fiber,” or its FiberPlus Antioxidants Chocolatey Peanut Butter Chewy Bar, with “35% DV fiber,” for breakfast?

Why bother eating a fiber-rich orange (that you have to peel) or a peach (that might drip on your clothes) when you can snack on a Fiber One Double Chocolate Cookie or a Fiber One 90 Calorie Chocolate Fudge Brownie, each with “20% Daily Value of Fiber”?

You can even have a Weight Watchers Chocolate Crème Cake, with 4 grams of fiber, or a Skinny Cow Chocolate Truffle ice cream bar, with 3 grams.

Those and other cookies, brownies, bars, “fruit” snacks, drinks, muffins, and white-flour pastas and breads get much of their fiber from white powders like inulin, polydextrose, and modified starches.

The problem: most processed fibers don’t do as much as intact, unprocessed fiber.

“Epidemiological studies show that eating fiber-containing foods like fruits, vegetables, whole grains, and legumes has many good health outcomes,” says Joanne Slavin, professor of nutrition at the University of Minnesota. “That’s pretty solid.”

The evidence is strongest that those foods can lower the risk of heart disease, concluded the Institute of Medicine in 2002. But they may also help prevent constipation, type 2 diabetes, and obesity.

“But all these added fibers are really different,” explains Slavin. “If people think, ‘I’ll get nine grams of fiber in this chocolate bar and I won’t have to worry about getting enough fiber,’ that’s a mistake.”

Marketers’ biggest lure: the claim that fiber leads to weight loss by making you feel full.

Fiber “helps provide a feeling of fullness,” says the Thomas’ Light Multi-Grain Hearty English Muffins package.

“Most added fibers don’t affect satiety,” says Slavin. “If you can sneak added fiber into a food or drink and it doesn’t affect the taste, it’s not likely to have any effect on satiety.”

For example, when she gave 22 women chocolate crisp bars with 10 grams (a fairly high dose) of one of four processed fibers—inulin, oligofructose, soluble corn fiber, or resistant wheat starch—they felt no less hungry than when they got bars with no added fiber.

“Inulin is a prebiotic, but it probably shouldn’t be labeled as a fiber,” notes Slavin. (A prebiotic spurs the growth of bacteria in your gut.)

In another study, people were no less hungry after eating muffins made with 10 grams of added polydextrose than after eating a low-fiber muffin, though they were less hungry after eating muffins with 10 grams of resistant starch or corn bran.

“If you look at any added fiber, half of the studies show something and half show nothing,” says Slavin. “It takes a high dose of fiber to show an effect. At the amount that people typically eat, it’s not going to show anything at all.”

Foods that are rich in intact fiber (fruits, vegetables, beans, and whole grains) are a different story.

“In our studies, people do feel fuller with higher-fiber whole foods,” says Slavin. In one study, she gave 14 women one of two breakfasts: oatmeal, blueberries, and apples or a glass of skim milk and roughly two cups of Naked juice plus Fibersol-2, an added fiber. Both breakfasts had the same calories and the same amount of fiber (10 grams), protein, carbohydrate, and fat.

“People felt fuller on the oatmeal and fruit,” says Slavin. “To say that if we put some fiber in a drink, it’s going to make you feel fuller, that’s misleading.”

Can processed fibers help keep you regular? Even high doses (20 grams a day) of inulin don’t. The same high dose of polydextrose increased stool weight, but “the increase was about 25 percent of that seen with wheat bran,” says Slavin. And the people who got the polydextrose also reported more gas.

Similarly, “there is some data showing that some processed oat, soy, or corn fibers increase stool weight, but it’s not much of an increase,” adds Slavin.

And it’s not easy to tell which fibers provide even that small increase.

“They vary all over the place,” says Slavin. “You can isolate the fiber in oats by different methods. Some are really gummy, so they’re good for lowering blood cholesterol. An isolated oat hull is not. It’s complicated.”

The bottom line: added processed fibers don’t turn cookies, brownies, bars, and shakes into beans, bran, berries, and broccoli. But they do turn little white powders into bigger profits.

Sources: J. Acad. Nutr. Diet. 112: 1356, 2012; Nutr. Res. 29: 100, 2009; Appetite 57: 38, 2011; Food Funct. 2: 72, 2011; J. Nutr. 143: 473, 2013.

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