Soluble Fiber vs. Insoluble Fiber and Why Your Body Needs Both

Load up on both fiber types for a healthy gut and balanced diet.

When trying to make dietary changes to live a healthier lifestyle, the options can seem overwhelming. There are various types of food plans claiming that by increasing or decreasing a particular macronutrient, you can transform your health. But what if the secret to maintaining a healthy diet is much simpler than all that?

Fiber is one of the most important factors to consider when evaluating what we eat, but it often gets overlooked. While we sometimes think of fiber as the stuff that helps keep us regular in the bathroom, it does so much more than that.

Eating a high-fiber diet is important for maintaining blood sugar, fueling digestion, feeding gut bacteria, and lowering your risk of developing heart disease. Yet most U.S. residents don't get nearly enough fiber. "More than 90 percent of women and 97 percent of men do not get enough fiber daily, and thus, dietary fiber is a dietary component of public health concern," says Amy Gorin, MS, RDN, a plant-based registered dietitian.

Soluble and Insoluble Fiber

So what exactly is fiber, anyway? Fiber is a type of carbohydrate that your body can't digest, which means that it passes through your body relatively intact (but doing a lot of work along the way).

While all fiber is good, it's important to know there are two types of fiber, each behaving very differently in the body. "Soluble fiber is found in foods such as oat bran, nuts, seeds, beans, lentils, and some fruits and veggies," explains Gorin. Soluble fiber soaks up water and dissolves, creating a gel that moves slowly through your digestive tract. "This type of fiber helps to bulk up stool and prevent constipation."

On the other hand, insoluble fiber is found in foods such as whole grains and vegetables. "It helps stool to pass, meaning it helps get things moving through your digestive system and also helps bulk up your stool," says Gorin.

Insoluble fiber can be hard to digest and is sometimes the culprit for digestive distress, such as sensitivities when eating gluten or other grains or the reason why you get a little gassy or bloated after eating too many raw vegetables. Its bulk also has the benefit of filling your tummy after eating, leading to more feelings of satiety.

If you want to reap all the benefits that fiber offers, aim to incorporate sources of both soluble and insoluble fiber at every meal and snack. "This requires some planning, but after a while, it will become second nature," Gorin says.

Try having a piece of sprouted grain toast with avocado and an egg for breakfast, a side of sauteed spinach with lunch, and an afternoon snack of a small handful of nuts with a piece of fruit. If you follow that up with a dinner full of veggies and legumes (like these tasty and easy-to-make Cuban black beans with rice), you'll be well on your way to reaching your fiber goals and feeling your best.

A variety of dry beans on a wooden table

F.J. Jiménez / Getty Images

Foods Rich in Both Soluble and Insoluble Fiber

Sprouted Grains

Bread made from whole grains that have been allowed to begin to sprout before baking offers a higher amount of soluble fiber per serving than most bread on the shelves. Brands like Angelic Bakehouse and Ezekiel specialize in sprouted grains and can be found in grocery stores across the country. How do they stack up to their regular counterparts?

"The Angelic Bakehouse 7-Grain Bread, for example, provides an ample amount of fiber—an incredible 4 grams per slice, which is 14 percent of the daily value," says Gorin. "This is largely due to the fact that the bread's first ingredient is sprouted whole grains, which are made of fiber-boosting red wheat berries, quinoa, millet, oat groats, barley, rye berries, and amaranth."

Sprouted grains contain both soluble and insoluble fiber. Still, their higher content of soluble fiber than traditional bread may make them easier for some people to digest who are sensitive to digesting grains.

Beans

These might be one of the first foods you think of when you think of fiber—and with good reason! "Beans, including white and black beans, provide a combination of soluble and insoluble fiber. Fiber is great for stimulating digestion, as well as feeding gut bacteria," explains Gorin.

Prunes

Prunes, dried plums, and prune juice are excellent sources of both soluble and insoluble fiber. "Another benefit for digestion is that prune juice is a natural source of sorbitol, which helps to stimulate digestion by moving water into the large intestine," Gorin says. The natural laxative effect of prunes means they're commonly recommended as a natural remedy for constipation, but don't worry—they won't have the same harsh effects as some of the over-the-counter laxative remedies found at the pharmacy.

While most fruits, vegetables, and grains contain both soluble and insoluble fiber, some are better sources of one than the other.

sliced citrus on a blue cutting board

BHG/Michelle Parkin

Soluble Fiber Foods List

Oats

Oats are a great source of a specific type of soluble fiber called beta-glucan, which has been shown to play a unique role in lowering LDL ("bad" cholesterol). Starting your day with 1 cup of cooked oats (that serving size is for cooked oats, not dry oats) will deliver 4 grams of fiber, or about a fifth of what you should eat on a daily basis.

Brussels Sprouts

While many vegetables contain some soluble fiber, most vegetable fiber ends up being the insoluble kind. However, a 1-cup serving of cooked Brussels sprouts contains about 4 grams of total fiber, a little over half of which is the soluble kind.

Citrus Fruits

Compared to other fruits, citruses like oranges, grapefruits, and lemons are unique in their high ratio of soluble to insoluble fiber. A small orange contains about 1.37 grams of soluble fiber, compared to only 0.2 grams in a similar serving size of grapes or cantaloupe.

Bowl of almonds

Ekapat Suwanmanee /EyeEm/Getty Images 

Insoluble Fiber Foods List

Nuts

Nuts are one of the best sources of dense amounts of insoluble fiber. Almonds, for example, pack about 14 grams per cup. It's worth noting that nuts are much more calorie-dense than veggie sources of insoluble fiber, so you don't want to overdo it. But a sprinkle of pine nuts on your veggies or a handful of pistachios for a mid-morning snack is a great way to supplement your fiber intake.

Broccoli

Many vegetables are excellent sources of insoluble fiber, and broccoli is right at the top of the list, with about 4 grams per cup. Frankly, all members of the brassica family (cauliflower, cabbage, turnips) are excellent choices to up your intake of insoluble fiber. Increasing your overall veggie intake is a surefire way to eat regular insoluble fiber due to vegetables' high nutrient levels.

Wheat Bran

Wheat bran, a byproduct of the wheat milling process, is another condensed source of insoluble fiber. Half a cup will give you 13 grams of fiber, more than 90 percent of which is the insoluble kind. It has a sweet, nutty flavor and can be added to baked goods and cereal or used to top smoothies or yogurt.

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Sources
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