Cereal and fruit for breakfast, Fiber for gut health

“Fiber is your friend.”

“Eat more fiber.”

“Fiber helps you poop.”

Fiber, a topic you may feel well-versed about, may not be as straight forward as you think! While it is well established that fiber is a beneficial and necessary part of a healthy diet, there are many misconceptions about the role of fiber for gut health. Find out the real way fiber works to improve gut health and the specific types of fiber you need to load up on.

What is fiber?

Dietary fiber is the indigestible “roughage” from plants.

Plant foods include: grains, lentils, beans, peas, vegetables, fruits, nuts and seeds. Essentially, a plant is anything that grows from the Earth. So, if the food didn’t grow from the ground, it probably does not naturally contain dietary fiber.

Keep in mind that if these “plants” are highly processed (i.e. wheat kernel processed into white flour), the fibrous portion of the plan is often removed. The fiber is found on the outside portion of the wheat kernel, also referred to as the bran. When flour is white, soft and perfect for those baked-goods, the bran portion is removed, leaving you without fiber. 

wheat kernel

Fiber does not break down by the body’s digestive enzymes, unlike other types of foods (i.e. carbs, proteins and fats).  Therefore, fiber does not contribute calories (energy) to the diet. Instead, fiber is fermented by bacteria in the gut, or eliminated in the stool. 

How much fiber do I need?

Fiber needs are typically based on the total calories one consumes and is estimated based on 14 grams per 1000 calories. For simplification purposes, the the Daily Value (DV) of total fiber for 2,000 calorie diet is 25 grams per day. Typically, women need about 21 to 25 grams per day and men need about 30 to 38 grams per day, but these estimates are based on differing calorie needs. Therefore, if you eat more food than you need more fiber!

While most Americans consume a high-carbohydrate diet, unfortunately most of the carbohydrates are highly processed. That means the fiber is not present. The average American consumes <15 grams of fiber per day. 

Here’s a list you can download for a quick reference on the fiber content of various foods: Fiber Guide If you start increasing your fiber intake, the golden rule is you MUST simultaneously increase your water intake. 

Benefits of fiber-

There are many health benefits of consuming fiber including:

Reducing the risk of developing colorectal and other types of cancers 

Enhancing immune function

Lowering blood glucose levels

Achieving and maintaining a healthy body weight 

Bowel regularity 

Controlling cholesterol levels 

What are the different types of fiber?

All fiber is not created equal. Different types of fibers serve different roles in the body. Your primary focus, for general health purposes, should be to reach your total fiber grams each day. Don’t sweat the small stuff. However, for all of the Nutrition-Nerds out there, let’s dive into all of the ways to categorize fiber types…

Ways to classify fiber:

  • Natural Fiber vs. Synthetic Fiber 

    • Natural fiber comes from plants (i.e. inulin is the natural fiber of chicory root) vs synthetic fiber is created in a lab (i.e. polydextrose is a synthetic fiber of combining sorbitol and glucose)
  • Dietary Fiber vs. Functional Fiber 

    • Dietary fibers are any non-digestible carbohydrates (i.e. pulp of fruit) vs. functional fibers are non-digestible carbohydrates that are also proven beneficial to the body (i.e. prebiotics like Jerusalem artichoke) 
  • Supplemental Fiber vs. Whole Food-Based Fiber

    • Fiber supplements come in powders, capsules and even gummies and typically contain one isolated type of fiber (i.e. Metamucil contains psyllium husk) vs. whole food-based fiber indicates you get the fiber from eating the entire food (i.e. bowl of oatmeal with berries & nuts)
  • Soluble Fiber vs. Insoluble Fiber

    • Soluble fiber indicates the fiber dissolves in water (i.e. b-glucan found in oats) vs. insoluble fiber indicates the fiber does not dissolve in water (i.e. bran from whole grains)
  • Highly Viscous Fiber vs. Non-Viscous Fiber

    • Highly viscous fiber means the fiber forms into a gel when it interacts with water (i.e. psyllium husk) vs. non-viscous fiber means the fiber has no gelling abilities (i.e. inulin)
  • Fermentable Fiber vs. Nonfermentable Fiber 

    • Fermentable fiber is also known as prebiotic fibers that provide a fuel source for probiotics (i.e. fructooligosaccharides, resistant starch) vs. nonfermentable fibers remain intact throughout the colon and exit the body via the stool (i.e. wheat bran). 

As you can tell, there are many different attributes of fiber, playing different roles on the body. Remember, a food may contain more than one type of fiber. Additionally, a type of fiber may have numerous characteristics. For instance, psyllium fiber is soluble, nonfermentable and highly viscous. Due to this dynamic nature,  stick to my initial recommendation stated above: achieve total fiber grams each day, from a variety of fiber-rich sources, rather than sweating the details. 

Okay, so let’s shift the focus specifically to gut health.

How does fiber work to improve gut health?

Ideally, everyone is free of constipation and diarrhea, achieving the perfect bowel movement (BM) each day! This would put you at a 4 on the Bristol Stool Scale (pictured below). Bristol Stool Scale

Unfortunately, this is not often the case, at least in the clients I work with. To achieve the perfect BM, stool must have the optimal consistency so that it can pass completely without discomfort, pain, or straining.

To achieve the optimal stool consistency, two components are necessary: 

  1. Stool softening
  2. Stool bulking 

Certain fiber types helps with these components! Particularly, the nonfermentable (not fermented/consumed by bacteria in the gut) and highly viscous (gel forming when in contact with water) fibers are the ones you are after. 

Here’s how fiber helps create those perfect BMs:

  • Mechanical Irritation-

    • Insoluble fiber (the type that does not dissolve in water, like wheat bran), remains intact as it enters the colon.
    • The fiber particles come in different shapes and sizes. The coarser/larger insoluble particles irritate the lining of the colon.
    • Irritation causes tiny abrasions that increase the release of water and mucous in the colon. Stool can easily pass right along!
      • If you are dealing with an inflamed gut (i.e. Diverticulitis or Ulcerative colitis flare), avoid this type of fiber until things cool down. 
  • Water-Holding Capacity-

    • Highly viscous, gel-forming fibers (like psyllium husk) can hold on to a lot of water, preventing stool from getting too dehydrated.
    • The stool is softer, bulkier and easier to pass when it contains the ideal amount of water (~75% water). 

Fibers recommendations for gut health- 

Specific fiber recommendations may vary from person to person based on their medical history and health goals. However, for a generally healthy gut and optimal bowel regularity aim to include coarse insoluble fiber like wheat bran as well as gel-forming, non-fermentable fiber like psyllium husk (5g twice per day with water)


Take-home Message-

Dietary fiber is an essential part of the diet. By understanding how different fiber types interact with the body, you can develop an ideal fiber strategy. Fiber is your friend, but may be a more complex topic than you once thought! Stay tuned for more articles about fiber types and other gut-health topics. 


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  2. http://www.medscape.com/viewarticle/804450
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