If you’re not keen on foods that are naturally high in fiber—such as oatmeal, lentils, broccoli and peas—you may be tempted to choose fiber-fortified foods as a way to get your roughage. Manufacturers are putting isolated (“functional”) fibers in foods such as yogurt, ice cream, sugary cereals, energy bars, even juices and water, in order to make “high-fiber” claims. Dietary fiber, found in plant foods, promotes good bowel function and lowers blood sugar and cholesterol, among other benefits. The general recommendation is to get 14 grams of fiber for every 1,000 calories you consume. But are fiber-fortified foods as good as those that contain intact, naturally occurring fiber?
Teasing apart the fibers
Isolated fibers are either extracted from foods or chemically synthesized. They include inulin (from chicory root), pectin, polydextrose, methylcellulose and maltodextrin. If you see a highly refined food, such as white bread, or a food that normally contains no fiber at all, such as yogurt, that lists a fair amount of fiber on the nutrition label, chances are you’ll find one or more of these isolated fibers in the ingredients list. In contrast, if you see wheat bran, corn bran or oats on the ingredients list, for instance, you’re getting natural intact fiber.
Food companies also use small amounts of isolated fibers for a variety of reasons other than their fiber—for instance, to replace fat and sugar in salad dressings, dairy foods and frozen desserts; thicken puddings; prevent separation in chocolate milk or add crispness to pizza crust.
Isolated fibers have health benefits on their own (see below). But there’s not much evidence that adding fiber to food has the same effects as eating foods that are naturally high in fiber. The research on isolated fibers is inconsistent, and much of it is funded by manufacturers. Often, the amount of fiber added is too little to matter.
Moreover, different dietary fibers have different physiological effects, and many fiber-fortified foods contain only one type of fiber, not the range found in naturally high-fiber foods. Keep in mind, too, that it’s not even clear whether all or most of the benefits of a high-fiber diet, such as decreased risk of heart disease, come from the fiber itself or from the vitamins, minerals and other plant compounds that accompany the fiber.
Cases in point
- Not all isolated fibers do much to keep you regular—a prime reason why people seek out high-fiber foods. Some, like cellulose and pea or oat hull fiber, help constipation, says Wendy Joanne Dahl, Ph.D., R.D., assistant professor of food science at the University of Florida, while others, such as maltodextrin, won’t help much.
- Many isolated fibers lack the gumminess that natural soluble fibers have, which is what’s key in their ability to help control blood sugar and cholesterol levels. Polydextrose and maltodextrin, for example, are not gummy (who wants gummy orange juice?) and thus won’t have these benefits. And it’s unclear how much of an effect inulin has on blood cholesterol.
- When consumed in large amounts, isolated fibers—such as oligofructose, polydextrose and inulin—can cause gas and bloating and have a laxative effect. And it’s easy to overconsume ice cream and other tempting foods that have fiber added to them, compared to foods that naturally contain fiber, such as broccoli.
Possible benefits of added fibers
As “prebiotics,” some isolated fibers stimulate the growth of friendly bacteria in the colon, which may have health benefits. In particular, inulin may help prevent substances from becoming carcinogenic in the colon and may also improve symptoms of inflammatory bowel disease, according to a review article published in the Journal of Nutrition.
Adding inulin to foods may enhance satiety (the feeling of fullness), studies have found. Other isolated fibers may also have this effect, as does natural fiber. What's more, there’s some evidence that inulin may boost absorption of minerals, particularly calcium and magnesium. Yogurt with added inulin may thus be an especially good way to get calcium.
Finally, fiber fortification has allowed manufacturers to reduce the calories in some foods because the fiber is replacing some of the sugar, refined flour and/or fat.