Fiber is a nonnegotiable part of a healthy diet. Insoluble fiber is particularly important when it comes to keeping your digestive tract running smoothly. Sources of insoluble fiber include wheat bran, vegetables and whole grains.
About Soluble and Insoluble Fiber
Dietary fiber comes in two types: soluble and insoluble. Soluble fiber, found in oatmeal, dried beans and some fruits and vegetables, dissolves in water. It's made up of plant pectin and gums; the gel it creates during digestion helps your digestive tract run smoothly and protects against some chronic diseases.
Soluble fiber is also the type that can be quite beneficial when it comes to diabetes. A study published in Experimental and Therapeutic Medicine in August 2016 suggested that increased and regular consumption of soluble fiber significantly improved blood glucose (sugar) levels, insulin resistance, and metabolic profiles — particularly in people with type 2 diabetes.
Insoluble fiber, however, doesn't dissolve in water. You may hear it referred to as the "roughage" you eat. It's made up of plant cellulose and hemicellulose.
Insoluble fiber draws water into your stool, so your bowel movements become softer and move more easily through your digestive tract. Insoluble fiber makes up the majority of fiber in most fibrous foods. If you're constipated or trying to prevent constipation, insoluble fiber is the type of fiber on which you need to focus.
The Academy of Nutrition and Dietetics explains that you need both types of dietary fiber in your diet. Both fibers are a type of carbohydrate, but neither supply calories or can be used for fuel. So, if you're watching your weight, you don't have to worry about fiber-dominant foods contributing to an elevated calorie intake. In fact, many of the foods that contain fiber — such as raw fruits and vegetables — are ideal for a healthy, weight-maintaining diet.
The recommended amount of dietary fiber for regular consumption is 14 grams for every 1,000 calories you eat per day. This comes out to a general recommendation of about 25 grams daily for women and 38 grams daily for men. The University of California San Francisco explains that while no single dietary reference intake for each specific type of fiber exists, you should aim for about one-quarter of your daily fiber intake to come from soluble fiber. The rest can come from insoluble sources.
In March 2015, Nutrition Today published a paper noting that as many as 90 percent of all Americans fail to get the recommended dose of 25 to 38 grams of daily dietary fiber, with the average consumption being just 15 grams per day.
Insoluble Fiber Benefits
Fiber, in general, is an important part of a healthy diet. The Academy of Nutrition and Dietetics goes on to explain that adequate fiber intake can help reduce cholesterol, and thereby help prevent heart disease. Fiber also helps with weight management, by slowing the speed at which food passes through the stomach, making you feel fuller longer.
Fiber increases the bulk in your digestive tract, so your bathroom visits become more regular and constipation isn't an issue. Constipation can lead to serious complications, including hemorrhoids, anal fissure, fecal impaction and rectal prolapse, notes Harvard Health Publications. If consuming a little extra insoluble fiber prevents these nasty conditions, why do so many people avoid it?
A low-fiber diet is also associated with diverticulosis and diverticulitis, conditions that compromise the function of your large intestine or colon. Eat more insoluble fiber to keep your digestion and elimination systems healthy. Because insoluble fiber stays intact while traveling through the digestive tract, it's also less likely to contribute to gas.
The International Journal of Food Sciences and Nutrition published a research analysis of 376 papers in December 2018 which concluded that consuming an adequate amount of fiber is protective against colon cancer. Colon cancer is the third most common cancer, excluding skin cancers, according to statistics from the American Cancer Society.
Insoluble fiber, in particular, is especially helpful when it comes to experiencing health benefits. The position of the Academy of Nutrition and Dietetics, published in the organization's journal in November 2015, notes that insoluble fibers, particularly from whole grains, can reduce your risk of cardiovascular disease. Their analysis also found that consuming recommended amounts of fiber, including soluble and insoluble fiber, reduces gastric cancer risk.
The British Journal of Nutrition published research in November 2015 which showed that adequate fiber intake was associated with lower blood pressure levels in men and women aged 40 to 59. The researchers concluded that higher intakes of fiber, particularly insoluble fiber, may contribute to lower blood pressure levels.
Read more: The 14 Best Foods for Your Heart
Best Insoluble Fiber Foods
High-fiber foods often contain a mix of soluble and insoluble fiber. The Cleveland Clinic notes that good sources of insoluble fiber include whole bran, nuts, whole grain products, corn, carrots, grapes, berries, and apple or pear peels. If you're trying to increase your fiber intake, don't peel your fruits!
One cup of wheat bran contains 24 grams of fiber — almost a day's worth for many people. A quarter cup of almonds contains 3 grams. One cup of cooked brown rice or microwaved frozen corn also offers 3 to 4 grams of fiber. Indulge in one cup of fresh blueberries and take in 4 grams of fiber. One large carrot offers up 2 grams of roughage, or insoluble fiber, too. Cooked black beans provide 12 grams per cup.
Foods made with whole-wheat flour will also contain a notable amount of insoluble fiber. One cup of stone-ground whole-wheat flour contains 12 grams of fiber.
Nutrition labels and information don't break down the exact ratio of soluble to insoluble fiber in these foods. They merely list the total dietary fiber content in a food.
Fitting In Insoluble Foods
Reaching your recommended fiber levels is easy when you make some simple dietary changes. Whether you want to avoid constipation and the ugly side effects of discomfort, bloating and hemorrhoids, or are looking to boost your overall health, take these steps:
- Start every day with a whole-grain product. Try toast, bran cereal or a whole-wheat English muffin.
- Bake pancakes, cookies, quick breads and muffins with whole-wheat flour. If you're hesitant about the density the flour may create, replace just half of the white flour in the recipe with whole-wheat flour.
- Snack on nuts, such as almonds, walnuts and peanuts. You'll also get a dose of healthy fat.
- Experiment with new whole grains in soups, alongside stirfries, and to accompany stews. Try buckwheat, barely, quinoa or wheat berries, for example.
- Have a pack of baby carrots in the fridge that you can dip into sauces or add to salads for a quick fiber boost.
- Shop for whole-grain crackers, instead of the white refined types.
- Include black beans (or other legumes) in salads, wraps or tacos, or choose them as a side dish.
- Add a pear (with the skin) or a cup of grapes to your lunch.
As you increase your insoluble fiber intake, do so gradually, advises the Academy of Nutrition and Dietetics. The fiber absorbs water so it passes through and scrubs your system adequately. An increased consumption of insoluble fiber and not enough water could actually cause constipation and nausea — symptoms your fiber intake is supposed to help you avoid.
Read more: 19 High-Fiber Foods — Some May Surprise You!
Fiber Supplement Facts
It can sometimes be challenging to get all the fiber you need from your diet. You may find high-fiber foods unpalatable or hard to digest. Fiber supplements can offer you the soluble and insoluble fiber you need. But before you start a supplement, check with your doctor, advise the experts at the Cleveland Clinic. Your doctor can recommend the best option for your needs. Also, recognize that supplements with insoluble fiber usually have wheat or cellulose in the ingredient list.
Do make sure you drink plenty of water with your insoluble fiber supplements; not doing so can cause the fiber to swell and cause choking and constipation. How much water you need with your supplement should be detailed on the supplement's label.
The Academy of Nutrition and Dietetics warns, however, that you should really consider all the potential nutritious whole-food sources of fiber before reaching for a fiber supplement. If you're missing out on fiber, you might be deficient in other essential vitamins and minerals, too.
The 2015 Nutrition Today paper notes that fiber supplements do not provide the health benefits that are associated with dietary fiber from whole foods. Fiber intake is a good measure of your dietary quality. Consider keeping a food journal for a week or two to track your fiber intake and overall diet.
Insoluble Fiber Precautions
If you're prone to passing loose stool or diarrhea, increasing your insoluble fiber intake isn't a good idea. It could simply make the problem worse. Stick to foods that are primarily made up of soluble fiber, such as oats and bananas.
People with irritable bowel syndrome, or IBS, should be careful about the types of fiber they consume. IBS, a common gastrointestinal condition, affects as many as 10 to 20 percent of adults worldwide.
Don't avoid fiber categorically, because it offers valuable benefits such as lowering blood cholesterol levels, improving glycemic control and helping to manage your body weight. However, remember that insoluble fiber can contribute to symptoms such as abdominal bloating, distension and flatulence, according to a paper in the September 2017 issue of the Journal of Molecular Medicine.
Men and women with IBS should instead focus on long-chain, soluble fiber, such as that found in psyllium. This type of fiber is actually recommended as part of an IBS dietary management plan.
- MedLine Plus: "Soluble vs. Insoluble Fiber"
- Academy of Nutrition and Dietetics: "Fiber"
- University of California San Francisco: "Increasing Fiber Intake"
- Experimental and Therapeutic Medicine: "Therapeutic Effects of Aoluble Dietary Fiber Consumption on Type 2 Diabetes Mellitus"
- Journal of the Academy of Nutrition and Dietetics: "Position of the Academy of Nutrition and Dietetics: Health Implications of Dietary Fiber"
- British Journal of Nutrition: "Total, Insoluble and Soluble Dietary Fibre Intake in Relation to Blood Pressure: The INTERMAP Study"
- Cleveland Clinic: "Improving Your Health With Fiber"
- Food Data Central: "Wheat Bran"
- Food Data Central: "Almonds"
- Food Data Central: "Brown Rice"
- Food Data Central: "Corn"
- Food Data Central: "Blueberries"
- Food Data Central: "Whole Wheat Flour"
- Food Data Central: "Carrots, Raw"
- The Academy of Nutrition and Dietetics: "Easy Ways to Boost Fiber in Your Diet"
- International Journal of Food Sciences and Nutrition: "Is Dietary Fibre Truly Protective Against Colon Cancer? A Systematic Review and Meta-analysis"
- American Cancer Society: "Key Statistics for Colorectal Cancer"
- Nutrition Today: "Evidence-Based Approach to Fiber Supplements and Clinically Meaningful Health Benefits, Part 1"
- Food Data Central: "Black Beans"
- International Journal of Molecular Medicine: "Dietary Fiber in Irritable Bowel Syndrome (Review)"
- Harvard Health Publications: "Constipation: A Strain for Men"