Soluble vs. Insoluble Fiber: How to Choose

You probably already know that fiber is good for you, but did you know there are different types? The two main categories of fiber include soluble fiber and insoluble fiber, each playing different roles in the body and keeping it working optimally.

Depending on what your body needs, you may need a particular balance of the two, especially if you are managing a specific health condition. Below, a registered dietitian breaks down the difference between soluble and insoluble fiber so you can be sure you are getting enough of each.

Why Focus on Fiber?

Dietary fiber is an essential nutrient that passes through your digestive system without being digested and is found in plant-based foods such as fruits, vegetables, whole grains, legumes, nuts, and seeds. Fiber offers a number of health benefits and supports several body systems. Yet, many individuals don’t get enough.

According to the 2020-2025 Dietary Guidelines for Americans, adults need 22 to 34 grams of fiber daily, and more than 90% of Americans do not eat enough. On average, adults consume only about 15 grams of fiber, which is half the recommended amount.

Supporting your body with enough fiber promotes a healthy gut and reduces the risk of chronic diseases such as diabetes, heart disease, and certain types of cancer. Fiber also serves as a bulking agent in food and helps keep you full, which can aid in weight maintenance.

Types of Fiber and Their Roles

Fiber plays an important role in the body, and many plant foods contain both types of fiber—soluble and insoluble—but in different amounts. Here’s more on the difference between insoluble and soluble fiber and where you can find each type.

Soluble Fiber

Soluble fiber is helpful for digestion because it absorbs water and creates a gel-like substance in the gut as it dissolves. It also slows digestion and absorption, keeping you feeling fuller for longer. Because soluble fiber slows digestion, particularly of carbohydrates, it can help prevent blood sugar spikes and promote blood sugar control. Soluble fiber also binds to cholesterol in your food and carries it out of your body through stool. As a result, eating more soluble fiber may help lower blood cholesterol.

“For soluble fiber, some of my favorite foods include oats, apples, citrus fruits, seeds, and legumes,” says Jessi Holden, MS, RDN, a family-focused culinary registered dietitian of The Kitchen Invitation. “These foods not only provide fiber but also come packed with essential nutrients and flavors that can appeal to all members of a family.”

Insoluble Fiber

Insoluble fiber, as it sounds, does not absorb water and is the kind you turn to for better bowel regularity. According to Samina Qureshi, RDN, an irritable bowel syndrome (IBS) and gut health dietitian based in Houston, Texas, “Insoluble fiber helps food pass more quickly through the digestive system and adds bulk to stool.”

Because insoluble fiber makes stool softer and easier to pass, food particles do not stay in the colon for a long time. This can help lower the risk of colorectal cancer. Similar to soluble fiber, insoluble fiber also reduces insulin resistance and when combined with soluble fiber, can help decrease type 2 diabetes risk and improve blood sugar control.

Fiber Supplements

While it is helpful to start with food to increase fiber intake, a fiber supplement certainly has its time and place. “If you’re looking to boost your diet with fiber, remember to start slow and try a food-first approach rather than jumping head first into a supplement,” says Qureshi. “Too much too soon can cause digestive upset and worsen constipation if not properly hydrated.”

When high-fiber foods are limited, or you need an extra boost of fiber, supplements may be useful. Psyllium husk is an effective form of soluble fiber that can help reduce cholesterol, balance blood sugar, and promote smooth and regular bowel movements.

Inulin is another common fiber supplement from chicory root, a prebiotic that provides food for the healthy bacteria in your gut. Wheat dextrin, most recognizable as Benefiber, is a soluble fiber that helps to regulate digestion and stabilize blood sugar.

Holden also recommends incorporating flax meal into foods. “Flax meal incorporated more often can be a good choice since it is part insoluble and part soluble. [It] could be added to smoothies, oatmeal, jam, hummus, pizza, and many more foods.”

Which Fiber Do You Choose?

Holden says that gastrointestinal symptoms such as diarrhea, constipation, and bloating may require a fiber fix, but picking the right one is important for getting results. “If someone is struggling with diarrhea, they want to lean into soluble fiber. Whereas constipation means you would want to lean toward insoluble fiber.”

If you have IBS, soluble fiber can help manage gut health and decrease symptoms, says Qureshi. “Soluble fiber such as psyllium husk has been shown to improve both IBS-related bloating, gas, constipation, and diarrhea.”

If you want to increase your fiber intake to help reduce cholesterol, choose more foods with soluble fiber. Meanwhile, foods with soluble and insoluble fiber balance blood sugar and help you feel fuller for longer.

Some easy ways to boost your fiber intake include adding chia seeds and flaxseeds to morning yogurt bowls, making homemade oat bars, and keeping chopped carrots or peppers on hand to dip into hummus for a quick snack.

Bottom Line

Both soluble and insoluble fiber are crucial for supporting gut health, heart health, and blood sugar balance. Incorporating a good variety of both will keep your body functioning optimally.

If you want to increase your fiber intake, be sure to do so slowly and progressively and drink adequate fluids. Too much fiber too quickly may cause constipation. Consult a registered dietitian for specific and individualized recommendations for your goals and nutrition needs.