Soluble vs. Insoluble Fiber

By: Shaun Dreisbach  |  March/April 2016
You might be asking yourself what is the difference between soluble vs. insoluble fiber. "Soluble fiber absorbs water and bulks up in your stomach, which promotes a feeling of fullness. It's also the type that acts like a sponge on cholesterol," says Tanya Zuckerbrot, R.D., author of The F-Factor Diet. Good sources of soluble fiber include beans and lentils, as well as carrots, oatmeal, apples and citrus fruits. "Insoluble fiber is like nature's broom. It helps speed up the passage of waste through your digestive tract and reduces the risk of colon cancer and other diseases," she adds. "It's often referred to as 'roughage' because it comes from the woody, or structural, part of plants, such as broccoli stems, the outer kernel of corn, wheat and whole-grain cereals—as well as the skin and seeds of fruits and vegetables."
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You need both types of fiber in your diet, but experts say you don't need to worry about how many grams of each you get. Most fiber-rich foods contain some of both, anyway. As long as you eat plenty of vegetables, fruits, beans and whole grains that are high in total fiber, you'll get the benefits of both.
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And that's where reading labels comes in. Food manufacturers add all sorts of enticing labels to products—like "Whole grain!" and "Good source of fiber!"—but that doesn't necessarily mean they're the fiber powerhouses you're hoping for. Here's the deal: in order to be "high fiber" a food must contain at least 5 grams per serving (20 percent of the daily value) as required by the FDA. If it has between 2.5 and 4.9 grams a serving, it can be labeled as a "good source of fiber." And if it has at least 2.5 grams of added fiber (see "Are Manufactured Fibers as Good for You as Natural?"), the food can boast "more fiber" or "added fiber."
Products labeled "whole grain" can also lull you into a false sense of fiber-richness. "Whole grain means you're getting all three parts of the grain—including the bran, which is where the fiber is—so it's definitely more nutritious, but it does not guarantee that it's high in fiber," says Vandana Sheth, R.D.N., C.D.E., a spokesperson for the Academy of Nutrition and Dietetics. You'll have to look for the actual grams of fiber to know for sure.
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