Sources of Insoluble Fiber

by Katie Kirkpatrick

Despite the recommendation of the American Dietetic Association that adults consume 25 to 38 grams of fiber per day, most average Americans only consume 15 grams per day. Because of their different roles in your health, a mix of soluble and insoluble fiber is recommended. Insoluble fiber increases stool bulk and the transit time of food. Insoluble fiber is beneficial in reducing appendictis, constipation, diverticulosis and possibly colon cancer. Sources of insoluble fiber are plant based.


Insoluble fiber is found on the exterior and husk of plant foods like grains. Grains are one of the major sources of fiber in the American diet. Whole-wheat bread, wheat bran and corn bran are among the best known sources of insoluble fiber. Whole-grain breakfast cereals are an excellent source of insoluble fiber as they often contain wheat bran, among other grains. Brown rice, barley, couscous and bulgar are less well-known grains that provide insoluble fiber.


Cellulose, a component of plant cell walls, is a type of insoluble fiber. It is found in the exterior of vegetables. Carrots, cucumber, zucchini, celery and onion skins are all sources of insoluble fiber. Eat the peel of vegetables like cucumber and zucchini to maximize your fiber intake. Snack on carrot and celery sticks with hummus or low-fat bean dip to increase the fiber in your diet.


Fruit contains both insoluble, on the outer peel, and soluble, on the inside, types of fiber. The peels of apples and tomatoes are high in insoluble fiber. Membranes of fruits like oranges and grapefruit are excellent sources of insoluble fiber. The tiny seeds in strawberries, blueberries, cranberries, blackberries and raspberries also provide insoluble fiber. Top your breakfast cereal or yogurt with berries or snack on an apple or orange to add insoluble fiber to your diet.

Plant Proteins

Another source of insoluble fiber is plant proteins. Legumes are rich sources of fiber, but only contribute about six percent of fiber in the American diet due to its low consumption. The legume family includes beans, peas and lentils. Seeds such as sunflower seeds and pumpkin seeds contribute insoluble fiber. In addition, peanut and almond skins contain insoluble fiber. Swap meat for beans or lentils for a few meals a week and mix seeds, peanuts or almond into a trail mix for added fiber.

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About the Author

Katie Kirkpatrick has been writing nutrition articles since 2005. As a registered dietitian, her work has appeared in the "Massachusetts Dietetic Association Newsletter." Kirkpatrick holds a Bachelor of Science in dietetics from Miami University and a Master of Science in nutrition from Boston University.