What is Insoluble Fiber? A Dietitian Explains!
Did you know there are different types of fiber that offer unique benefits? This post written by a Registered Dietitian will introduce you to insoluble fiber, its health benefits, and foods high in insoluble fiber. It will also break down the difference between soluble fiber and insoluble fiber, and if fiber supplements may be right for you.
About Fiber:
Fiber is a type of carbohydrate that is found only in plant foods like vegetables, fruits, nuts, seeds, grains, beans and legumes. It is the part of plants that the body cannot digest or absorb.
Because the body can’t digest it, fiber passes through the digestive system without being broken down. Despite this, there are still many health benefits that fiber offers. There are different types of fiber, and each offer unique functions and health benefits.
Insoluble fiber is one of two different types of dietary fiber. By definition, the word insoluble means incapable of being dissolved. This means that insoluble fiber cannot be dissolved in water, while soluble fiber can.
It is an important component of a healthy diet, and it can be found in a variety of plant foods, from vegetables and grains to beans and legumes.
Soluble vs. Insoluble Fiber:
Soluble fiber dissolves in water and forms a gel. In the digestive system, this means that it attracts water, forming a gel and slowing down digestion, keeping you full for longer. It also binds to cholesterol and sequesters it out of the body.
Insoluble fiber cannot dissolve in water, therefore it does not form a gel in the digestive system. However, this doesn’t mean that it isn’t beneficial for your health.
Curious about both soluble fiber too? I wrote an entire post on soluble fiber, its health benefits, and foods high in soluble fiber.
Insoluble Fiber Benefits:
Insoluble fiber helps to keep you regular. Because the body can’t break it down and it does not dissolve in water, it instead adds bulk to the stool.
By adding bulk, this type of fiber helps to move the stool through your bowel more quickly, keeping bowel movements regular.
By helping to keep things moving, consuming insoluble fiber helps to keep your digestive system healthy and may even help to lower your risk of developing certain conditions like heart disease and colon cancer.
Insoluble Fiber Foods:
Remember, dietary fiber is found in plants. Foods that are high in insoluble fiber include fruits and vegetables, whole grains, nuts, and seeds. Let’s take a look at some of the best food sources of insoluble fiber:
Fruits High in Insoluble Fiber:
- Berries (including blackberries, raspberries, strawberries, and blueberries)
- Apples with skin
- Pears with skin
- Avocado
- Dried apricots, figs, prunes, dates and raisins
- Passionfruit
Vegetables:
- Turnips
- Green peas
- Okra
- Spinach
- Radishes
- Rutabaga
- Potatoes and sweet potatoes
Whole Grains:
- Wheat bran and wheat germ
- Oat bran
- Barley
- Oatmeal
- Quinoa
- Whole grain pastas and breads
- Popcorn
Nuts and Seeds:
- Flaxseeds
- Almonds
- Walnuts
Beans and Legumes:
- Black beans
- Kidney beans
- Lentils
- Chickpeas
- Edamame
- Lima beans
How to Eat More:
If you want to eat more insoluble fiber, add more of the foods listed above to your diet!
For Breakfast:
Have whole grain toast with almond butter and banana, or a nice bowl of creamy breakfast oatmeal or delicious overnight oats. More of a smoothie person? Try adding flaxseeds or sneak some spinach in your smoothie!
For Snacks:
Snack on some popcorn, or add it to a homemade trail mix! Try these high fiber plant-based snack ideas or even stir some walnuts into these one-bowl brownies.
For Main Meals:
To add more insoluble fiber to your roster of main meals, try making this delicious Peanut Noodle Salad with edamame. Or make these nourishing Black Bean & Sweet Potato Taco Bowls. Everyone loves potatoes, so why not serve these crispy Garlic Parmesan Roasted Potatoes and reap the benefits of fiber too!
Insoluble Fiber Supplements:
While there isn’t a recommended daily allowance (RDA) for insoluble or soluble fiber specifically, there is a daily recommendation for total fiber intake. Current recommendations range from 20-25g fiber per day for adult women and 30-38g fiber per day for adult men.
I recommend aiming to meet your fiber needs through food first. You can do this by eating more whole plant foods like fruits and veggies, whole grains, nuts and seeds, and beans and legumes.
If you struggle with constipation, a supplement containing insoluble fiber may be helpful for promoting regularity.
Most fiber supplements are made from fiber that’s been extracted from natural sources, like psyllium husk. Metamucil (made from psyllium) is a fiber supplement that contains both insoluble and soluble fiber, so it can help to bulk up the stool and relieve constipation. Citrucel (methylcellulose) mainly contains insoluble fiber so this may also help with constipation.
Keep in mind that fiber supplements (soluble or insoluble) should not take the place of a balanced diet rich in high-fiber foods. Before taking a fiber supplement, speak to your doctor or Registered Dietitian to determine which product and dosage will be right for you.
Connect with Hannah Magee, RD!
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