The Differences Between Soluble vs. Insoluble Fiber and Why You Need Both

Nutrition experts explain how the benefits of soluble vs. insoluble fiber compare and how to get a mix of each type in your diet.

Bowl of Oats and Bowl of Nuts
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Although a food's nutritional label seems all-encompassing, it doesn't call out every subtype of nutrient that's important to mix into your diet. Exhibit A: The general "dietary fiber" section isn't broken down into soluble fiber and insoluble fiber, specific kinds of fiber (much like types of fat) that offer unique health benefits.

So, what's the difference between soluble vs. insoluble fiber, anyway? Here, registered dietitians lay out the distinctions between the two fiber types and why they're so important for your health. Plus, you'll find foods high in soluble fiber and insoluble fiber and tips to help you increase your fiber intake without constantly needing to pass gas.

What Is Fiber?

Simply put, dietary fiber is a type of carbohydrate found in all plant foods (think: fruits, veggies, whole grains, beans, nuts) that your body can't break down, so the nutrient passes through your digestive system relatively intact before exiting your body via stool, says Alex Caspero, M.A., R.D., a registered dietitian and plant-based chef in St. Louis. "You can visually see fiber if you think about a celery stalk and all that stringiness that you can peel off — that's cellulose, that's literally fiber," she explains.

Fiber can be divided into two categories: soluble fiber and insoluble fiber, both of which have significant health benefits. That said, simply sticking with an eating style that's high in fiber overall can do you some good, which is why the United States Department of Agriculture recommends folks following 2,000-calorie diets consume at least 28 grams of fiber a day. "If you're eating a fiber-rich diet, you're also eating a very nutrient-dense diet," says Caspero. "You're eating a diet rich in antioxidants and various vitamins and minerals because you're eating a lot of whole plant foods."

What's more, these fiber-filled foods can make you feel physically satisfied, says Abby Chan, M.S., R.D.N., a registered dietitian nutritionist and the co-owner of EVOLVE Flagstaff in Arizona. Just think of a big, fiber-packed salad. Even though the meal may be low-calorie, "that's going to take up a lot of space in your stomach, which will make you feel full physically," she says. "But just because you are volume full does not mean you are satiated." In other words, even if that salad you polished off fills up your stomach, you might mentally be craving more — which is why it can be beneficial to pair your high-fiber foods with digestible carbohydrates, suggests Chan. "Our brain is the main utilizer of glucose, and [quick-digesting] carbs are going to be the thing that helps turn off your brain's hunger switch," soon after consumption, she adds.

What Is Soluble Fiber and What Are Its Benefits?

Just as the name implies, soluble fiber is a type of fiber that dissolves when exposed to water, creating a viscous, gel-like material, says Chan. When it enters your digestive tract, this jelly-like substance offers a few major health perks.

Helps Manage Blood Sugar Levels

Munching on a food high in soluble fiber helps slow down digestion, which in turn causes blood sugar to rise slowly after eating, says Chan. "For someone who has type 2 diabetes or diabetes in general, soluble fiber can be really beneficial to help them manage blood sugar levels," she adds. ICYDK, folks with type 2 diabetes don't produce enough insulin (a hormone that shuttles blood glucose into cells for energy) or doesn't use it properly, causing blood sugar levels to stay high, according to the National Library of Medicine. Over time, this can lead to health concerns such as heart disease, vision loss, and kidney disease, according to the Centers for Disease Control and Prevention (CDC). Since soluble fiber doesn't cause a spike in blood sugar like other carbohydrates, though, it can help these individuals keep their blood glucose within their personal target ranges, according to the CDC.

May Lower LDL Cholesterol Levels

Incorporating foods rich in soluble fiber into your meals may help lower low-density lipoprotein (aka LDL or "bad") cholesterol levels, says Caspero. Here's how it works: Soluble fiber traps bile (a fluid that assists in digestion, breaks fats down into fatty acids, and contains cholesterol) that's released in the small intestine after you eat a meal. This process prevents the bile from being reabsorbed further along in your digestive tract; Instead, it will exit your body through your stool, according to information published by Oregon State University (OSU). In other words, "​​soluble fiber will decrease how much [bile] your body can actually absorb, and that will decrease serum cholesterol and LDL cholesterol," says Chan. And this soluble fiber perk is important, as high levels of LDL cholesterol can raise your risk of heart disease and stroke, according to the CDC.

Feeds Beneficial Gut Bacteria

Even though your body can't break down soluble fiber, the gut bacteria that live in your large intestine can, says Chan. In this instance, the soluble fiber is acting as a prebiotic (aka food for your gut bacteria). When these microorganisms digest the fiber, it "results in the production of certain hormones that play a role in satiety, and they can produce short-chain fatty acids, which can increase the water in your stool and help with overall smooth bowel movements," says Chan. These short-chain fatty acids also have anti-inflammatory and anti-carcinogenic properties, she adds, and they've been found to protect against gastrointestinal bacterial pathogens, according to the information published by OSU.

What Is Insoluble Fiber and What Are Its Benefits?

Unlike soluble fiber, insoluble fiber doesn't dissolve in water, says Chan. Instead, this type of fiber attracts and absorbs water, which creates bulkier, softer stools and makes it easier to have a bowel movement, adds Caspero. But that's not the only benefit insoluble fiber has to offer.

Keeps You Regular

Not only does insoluble fiber change theconsistency of your poop for the better, but it also speeds up transit time — the amount of time it takes for food to exit through your poo after consumption, says Chan. "You're going to have more consistent and more reliable bowel movements," she says. This benefit not only helps fend off constipation, but it also can prevent uncomfy G.I. symptoms in folks with digestive disorders such as IBS or Chron's disease, says Chan. "For these people, the longer things are sitting in their digestive tract, the more it can lead to bloating, gas, and discomfort," she says.

Soluble vs. Insoluble Fiber Foods

Regardless of the plant food you're consuming, you'll nab a mix of both soluble and insoluble fiber, says Chan. Still, some foods are higher in the soluble fiber department than others, and vice versa.

Foods High In Soluble Fiber

To get a rough idea of which foods are high in soluble fiber, think about how they react when placed in water. If you were to soak oats, chia seeds, or ground flaxseeds in water, for instance, they'd turn gooey and viscous — signs that the soluble fiber is dissolving in the fluid, says Chan. "This isn't scientific, but I like to think that if the food turns into a baby food consistency, cooked or that's how it is normally, it's probably going to be higher in soluble fiber," she adds. To keep your blood sugar and cholesterol levels in check, consider mixing these foods rich in soluble fiber into your meals, according to Chan, Caspero, the Mayo Clinic, and the CDC.

  • Apples
  • Avocados
  • Bananas
  • Barley
  • Beans and legumes
  • Brussels sprouts
  • Chia and flax seeds
  • Citrus fruits
  • Oats
  • Peas
  • Psyllium

Foods High In Insoluble Fiber

If you were to drop a high-insoluble-fiber food, such as a carrot, in water, it'll remain intact — not puff up and dissolve as foods packed with soluble fiber do, Ashley Munro, M.P.H., R.D., a certified intuitive eating counselor in Tucson, Arizona, previously told Shape. To get your fill, try adding these insoluble fiber-rich foods to your plate, according to the Mayo Clinic and CDC.

  • Cauliflower
  • Green beans
  • Nuts
  • Potatoes
  • Seeds
  • Skins of fruits and vegetables
  • Whole wheat flour
  • Wheat bran

Should You Plan Your Soluble vs. Insoluble Fiber Intake?

Although it's important to score a mix of both soluble fiber and insoluble fiber, you don't need to stress yourself out over it and micromanage your consumption. "I know there is a distinction [between the fiber types] and sometimes that's helpful, but the vast majority of Americans — 95 percent — don't get enough fiber overall," says Caspero. "A lot of foods contain both soluble and insoluble fiber, so if you're just focusing on getting more fiber, you're going to be able to check both the boxes."

However, there are some instances in which it may be beneficial to take a slightly more strategic approach to your soluble vs. insoluble fiber intake. "If you're on a low-carb diet, you're eliminating a large amount of whole grains, beans, and a lot of these starchier foods, so you're probably not going to be getting enough soluble fiber, which can lead to more constipation," says Chan. In that instance, you might want to plan out how you'll nab soluble fiber in order to keep your number twos running smoothly. The same rule of thumb applies to folks who have elevated LDL cholesterol levels and are making dietary changes to reduce it, adds Caspero. "We may focus a little bit more on making sure that they're getting enough soluble fiber," she explains. "But it's hard to tease it out, and if you're focusing just on fiber in general, you're going to get enough."

How to Get Enough Soluble and Insoluble Fiber Through Your Diet

Ramping up your fiber intake should be a low and slow process, says Caspero. If you suddenly triple your fiber intake from one day to the next, you'll likely experience G.I. distress, she says. "You need to almost teach your body to slowly start to ferment and get used to these fibers so you're not having gas, bloating, cramping, diarrhea — all side effects of getting too much fiber too quickly," she says.

To take that gradual approach, first try incorporating a fruit, veggie, or whole grain into one meal or snack, suggests Chan. If you typically eat white rice at dinner, try swapping it with brown rice to increase your fiber intake, says Caspero. Stick with that alternative for a few days, then add beans on your salad instead of your usual chicken, she says. Making these swaps over time, and allowing your body toacclimate toeach increase in fiber, can help prevent any digestive discomfort, says Caspero. (BTW, you don't have to give up foods to meet your fiber goals. If switching from white to brown rice, for example, isn't an option for you, load your plate with a larger helping of veggies instead, says Chan.)

Don't beat yourself up if fiber gets pushed to the back burner during a few of your meals. "Some days you're going to have less fiber, some days you're going to have more — it's all about what feels possible in the moment," says Caspero. "Especially with people dealing with increased food prices and accessibility, I think what you can do is going to look different from someone else — and that's okay."

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