What’s the Deal with Fiber?

By Kelsey Chadwick, MS RDN

September 9th, 2024

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Fiber, fiber, fiber. Fiber is something I often talk about in my sessions with clients and for a good reason. Fiber plays many important roles in our body. Fiber is a type of carbohydrate that the body can't fully digest. Most carbohydrates are broken down into glucose, a type of sugar molecule, but this isn't the case for fiber. It actually passes through the body undigested. So now you're probably wondering what the point of fiber is if we aren’t digesting it. 

Some key roles fiber plays are regulating the body’s blood sugar, leading to more sustained fullness after eating, it can help lower our cholesterol, and contributes to regular and more comofortable bowel movements.

Fiber naturally occurs in plant based foods. There are two types of fiber, soluble and insoluble fiber. Soluble fiber dissolves in water and is the type of fiber that can help lower blood cholesterol and delay blood sugar rises after a meal. Insoluble fiber does not dissolve in water, which helps food move through our digestive system, helping with regularity and constipation. 

Additionally you may hear of fiber as being fermentable and this is because it acts as food for gut bacteria that break down and ferment it. These foods are known as prebiotics. You can check out more on this topic in an earlier blog post here.

Naturally occurring plant fibers include funky names like beta-glucans, guar gum, cellulose, hemicellulose, lignins, inulin, oligofructose, oligosaccharides, fructooligosaccharides, pectins, and resistant starch. There are also manufactured functional fibers, some of which are taken from natural plants and then modified.

I’d like to break down these funky words a bit. Oftentimes you might have heard “if you can’t pronounce it you shouldn't eat it” and quite frankly I think that is pretty bad advice! Science is a crazy and complex thing and with that comes many complex names. This certainly doesn't mean we shouldn't eat a certain food. If you needed a life-saving or life -changing medication for a medical condition but you couldn't pronounce it, would you still take it?

Beta-glucans are a type of soluble fiber found in oats and barley. It acts as a prebiotic and is highly fermentable. It does not have laxative effects but does add bulk to stool. It also helps to regulate blood glucose and cholesterol levels.

Guar gum is also a soluble fermentable fiber that is isolated from seeds. It does not have a laxative effect and also helps to regulate blood glucose and cholesterol levels. It has a gel-like texture and is metabolized and fermented in the small intestine.

Cellulose/hemicellulose is an insoluble fiber found in cereal grains and in many fruits and vegetables. It absorbs water, adding bulk to stool creating a laxative effect. Lignins are also a type of insoluble fiber found in wheat, nuts, flaxseeds, unripe bananas, corn bran and vegetables.

Inulin, oligofructose, oligosaccharides and fructooligosaccharides are fermentable soluble fibers that help to bulk stool with a laxative effect. They also can help regulate blood glucose and act as a prebiotic. These are found in onions, chicory root and asparagus and some other common plant foods.

Pectins are a type of soluble fermentable fiber. It has gelling properties and is found in fruits like apples and blueberries. It is known for helping to normalize blood sugar and cholesterol levels.

Resistant starch adds bulk to stools and helps normalize blood sugar and cholesterol levels. They are found in pasta, potatoes and legumes.

Psyllium is a soluble nonfermentable fiber that is extracted from psyllium seeds. It holds onto water and softens stools. It has a laxative effect and is often found in high fiber cereals and many over the counter remedies for constipation.

Below is a list of both soluble and insoluble fiber sources that are great to include in your meals and snacks. If you feel you are not getting enough fiber, a great way to add some into your diet is through snacks. Add in a piece of fruit and cut up veggies to your afternoon snack. Over time this helps to gradually increase fiber.

Soluble Fiber:

Grains & Legumes

• Oats, oatmeal, oat bran (oat bran flakes, cheerios)

• Barley

• Millet

• Rice, rice crackers, rice cereals

• Pasta, noodles (including rice noodles)

• Fresh white bread (e.g. sourdough, French) 

• Quinoa

• Cornmeal (e.g. polenta, corn tortillas, grits)

• Flour tortillas

Vegetables

• Yams/Sweet potatoes Potatoes

• Carrots

• Parsnips

• Rutabagas

• Pumpkin

• Winter and summer

• Squash

• Beets

• Turnips

• Asparagus

• Brussels sprouts

• Broccoli

• Onion

• Cucumber

• Shiitake mushrooms

Fruit

• Apples, applesauce

• Banana

• Papaya

• Mango

• Avocado

• Apricots, fresh with skin

• Grapefruit

• Orange/clementine

• Peaches

• Plums

• Watermelon

Nuts & Seeds

• Chestnuts

• Chia seeds

Insoluble Fiber:

Grains & Legumes

• Whole wheat bread, pastas and cereals

• Wheat bran

• Wheat germ

• Popcorn

• Beans

• Peas

• Lentils

Vegetables

• Lettuce/Salads

• Green leafy veggies (spinach, collards and kale)

• Cabbage

• Celery

• Corn

• Peas

Fruit

• Apple with peel

• Dried fruit

• Berries

• Cherries

• Grapes

• Kiwi

• Cantaloupe

Nuts & Seeds

• Whole nuts

• Flax Seeds

• Sesame seeds

• Sunflower seeds