The Two Types of Fiber

When most of us think of fiber, we think of foods like whole grain bread and oatmeal. We think of them as ways to get our GI tract moving more quickly, foods great for when you have constipation or other stomach issues related to that. While all of this is true, fiber is actually a lot more complex. First of all, there are two types, each with slightly different functions in the body. These two types of fiber come in different types of foods. In today’s post, I’m going to discuss what fiber is and certain foods with each type and the functions of each.

What is Dietary Fiber?

According to my Medical Nutrition Therapy textbook, dietary fiber is defined as “edible plant materials not digested by the enzymes in the GI tract.” It includes cellulose, hemicellulose, pectins, gums, lignins, starchy materials, and oligosaccharides. Some foods that provide dietary fiber are whole grains, fruits, vegetables, legumes, nuts, and seeds. There are two types of dietary fiber: soluble and insoluble. The main difference is how they each react to water. Soluble fiber dissolves in water and GI fluids while insoluble fiber does not.

Soluble Fiber

assorted beans in brown sacks
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Foods High in Soluble Fiber

  • legumes
  • oats
  • barley
  • rye
  • chia seeds
  • flaxseeds
  • berries
  • bananas
  • pears
  • plums
  • prunes
  • carrots
  • broccoli
  • artichokes
  • onions
  • cooked pasta, rice, potatoes

Functions of Soluble Fiber

There are so many wonderful benefits of soluble fiber in our bodies. Because this type of fiber can absorb water, it forms a gel-like blob (for the scientific term…) in the GI tract. This blob can help with weight management and atherosclerosis because it blocks some dietary fat, including cholesterol, from being digested and absorbed.

It does something similar with sugar as well. Soluble fiber has been shown to lower blood sugar levels because the blob slows the digestion rate of carbohydrates. This prevents sudden spikes or dips in blood sugar. This is especially helpful for diabetics or those with hypoglycemia.

Soluble fiber is also what I like to call a “bacteria snack.” Because soluble fiber is fermentable in the gut, it is able to feed the healthy bacteria within your intestines. This improves many aspects of health, including digestion, the immune system, and brain function.

Lastly, one we probably all know, soluble fiber keeps you fuller longer. This is because it actually slows down digestion, and absorption of energy and nutrients is slowed and spread out over a longer period of time.

Insoluble Fiber

baked bakery baking board
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Foods High in Insoluble Fiber

  • whole grain products
  • bran
  • legumes
  • nuts
  • seeds
  • cauliflower
  • zucchini
  • celery
  • green beans
  • skin and pulp of fruits/vegetables

Functions of Insoluble Fiber

Like soluble fiber, insoluble fiber also has many important health benefits. This is the type of fiber that I usually think of when I think of “fiber” in general; this kind of fiber helps prevent constipation. Because it’s indigestible, it sits in the intestines absorbing fluid and other waste until it forms a stool. This process speeds of the removal of waste and therefore prevents a “back up.” For this reason, insoluble fiber isn’t the best idea when you’re suffering from diarrhea or malabsorption. If everything is already rushing through you, your goal is to slow things down, rather then speed them up, so your body is able to absorb nutrients again. However, this doesn’t mean you can’t eat any fiber. Soluble fiber is the way to go in this case.

Insoluble fiber is also a great way to keep you fuller longer. Though it doesn’t slow digestion like soluble fiber, it physically takes up space in your stomach and intestines, undigested. So you really won’t want to eat a whole lot. This is a great way to manage weight.

I’m kind of a fiber enthusiast and I love converting others! Hopefully you were able to learn a little bit more about fiber today and can somewhat understand my love for it. (: Thanks for reading!

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