What is Fiber?
Fiber typically appears in our diet in two forms: dietary and functional. Dietary fiber is found in the non-digestible carbohydrates of plant cell walls, such as in quinoa, brown rice, whole fruits, vegetables, nuts, and seeds. Functional fiber is isolated, extracted, or manufactured and added to processed foods like fiber bars, Metamucil, and Oli-pop. These can provide high amounts of fiber quickly, which can often lead to bloating and gas.
When we think about fiber coming from plants, it can be helpful to understand its source. You may have heard the terms “refined” and “unrefined” grains. The diagram below shows the breakdown of the different layers of a whole grain: Bran: Fiber-filled outer layer that also contains vitamins and minerals. Endosperm: Starchy middle layer. Germ: The nutrient-packed core.’
During the refining process, the bran and germ are removed, leaving only the endosperm. For example, brown rice (unrefined) retains its fiber and nutrients, while white rice (refined) has these layers stripped away.
Types of Fiber
When we consume whole grains, fruits, vegetables, nuts, seeds, or other plant-based foods, the fiber they contain can be classified into two types: soluble and insoluble fiber.
Soluble fiber becomes paste-like when consumed and forms a protective barrier in the small and large intestines. It also serves as a food source for healthy gut bacteria.
Insoluble fiber stays intact and helps bulk up stool. Humans lack the enzyme to break down the bran part of a carbohydrate, but gut bacteria can, making it a great fuel source for healthy intestinal bacteria.
Prebiotic and Probiotic Fiber
You may also hear about prebiotic and probiotic sources of fiber:
Prebiotic fiber sources that cannot be digested by humans but can be digested by gut bacteria. This type of fiber encourages the growth and activity of beneficial intestinal bacteria. We need prebiotic fiber to continue feeding and sustaining these beneficial bacteria.
Probiotics are live, bacteria that reside in your gut. They are found in foods that have undergone fermentation, such as yogurt, kefir, sauerkraut, kimchi, and kombucha. There are thousands of probiotic species isolated from humans, with more still being discovered.
Fiber Recommendations
The dietary recommendation for daily fiber intake is 25 grams. The average American typically consumes only 3 to 8 grams per day, leaving significant room for improvement.
Aim to get most of your daily fiber from whole foods like fruits, vegetables, nuts, seeds, and whole grains, as they also provide essential vitamins, minerals, and phytonutrients.
