Fiber

Overview

When humans eat plants (be it fruits, vegetables, grains, legumes, nuts, or seeds), nutrients like proteins, fats, carbohydrates, and others are digested and metabolized. However, there is a portion of plant matter that is indestructible, at least by a human gut’s standards. That portion is fiber.

Although fiber is not broken down by human digestive tracts, it is well known for its role in digestive health, and is important for general health overall.

Fiber, a type of complex carbohydrate, is broken down into two categories: soluble fiber and insoluble fiber. These two types are distinguished by their ability to dissolve in liquid, and each have their own unique health benefits. Soluble and insoluble fiber can be further broken down into different types of fibers, such as lignin, inulin, resistant starch, cellulose, beta-glucans, and others.

Importance

Soluble fiber, as its name implies, is soluble and will absorb liquids. Soluble fiber often has a sticky, gel-like quality to it, which means it can function to bind to things like excess cholesterol as well as lubricate the bowels. Soluble fiber has prebiotic activity, which means it acts as food for probiotics, the good bacteria in our bodies. Soluble fiber also lowers the glycemic load of a food, so can also help to regulate blood sugar.

Insoluble fiber does not dissolve in liquids. It has a rougher texture and adds bulk to food to help us feel satisfied. As it moves down the digestive tract, insoluble fiber also adds bulk to stool and aids in bowel movements.

Food Sources

Below is a list of food sources for both types of fiber. Note that some foods are found on both lists, as they contain a mix of soluble and insoluble fibers.

Soluble fiber is found in:

• Some fruits like figs, avocados, plums, and bananas
• Some vegetables like Jerusalem artichokes, carrots, broccoli, sweet potatoes, white potatoes, and onions
• Grains and legumes
• Nuts and seeds, like almonds, chia, flax, and psyllium

Insoluble fiber is found in:

• Whole grains (insoluble fiber is found in the bran portion of a grain) and legumes
• Some fruits and vegetables, particularly in the skins, or in more fibrous vegetables, such as celery or kale
• Nuts and seeds

Deficiencies

A diet low in plant matter will likely lead to fiber deficiencies. Staunch carnivores beware!

Most health experts recommend getting between 21-38 grams of fiber (from combined types) a day. Although fiber supplements exist, the best way to increase your fiber is by eating plants, which, along with fiber, come with a host of other health-benefiting vitamins, minerals, and phytochemicals.

Signs that you may have a fiber deficiency:

• Poor bowel regulation (either constipation or rapid transit time, i.e. loose bowels)
• Poor appetite regulation (for example, not feeling satisfied after meals or becoming hungry soon after a meal)
• Issues with blood sugar or cholesterol management

Excess/Toxicity

While fiber in excess is not toxic, it is uncomfortable. Commonly, too much fiber in the diet will manifest as gastrointestinal discomfort. Poor appetite, gas, bloating, constipation, and / or diarrhea may all be signs of too much fiber.

Recipe

For recipes rich in fiber, check out any of the Encyclopedia of Food entries for food items listed above.

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Related Foods

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  Sugar
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  Protein
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  Fats
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  Carbohydrates