NutritionWhat Does Fiber Do? (Part 3) Insoluble Fiber Deep Dive

November 8, 2021by Mike Phoutrides0

If you’re not one for detail, this blog post is not for you, so feel free to say no to this one, however if you have read What Does Fiber Do? (Part 1) and want to dive deeper on dietary fiber this is for you! This blog post is part three of a three-part deep dive into dietary fiber. The one you’re reading now is on insoluble dietary fiber, the other is on soluble dietary fiber. 

If you’ve already read part one, you’ll know what’s coming. That being said, a great first question is: how is this deep dive into insoluble dietary fiber going to help for weight loss?

The more implementable knowledge you have the better. This is going to sound self-serving, but the mission of Cornerstone Weight Loss is to help you better understand how food affects your body in a common sense way that will put you in control of how you look. You can definitely get to your weight loss goals without these dietary fiber deep dives, but the further you go into the “why” the more equipped you will be to have the control of looks and weight that you desire to have. (Not to mention you can pass this on to your friends and family and be that knowledgeable, helpful hero you’ve always wanted to be)!

We are going to just dive right into insoluble dietary fiber, if you’re looking for what total dietary fiber is and what it consists of, go to part one here.

So what’s insolubility all about anyway?

Solubility is about water and insoluble dietary fiber is not dissolved in water. If you’re looking for an easy example to think of, imagine the skins from apples; much of the insoluble fiber you eat comes from cellulose from the cell walls of plants. If you remember from the first article, a good amount of soluble fiber is able to be fermented by bacteria in your colon, which has a positive contribution to your body’s overall energy balance (calories-in). Insoluble dietary fiber, on the other hand, is mostly non-fermentable. This means that your body will not be able to digest it and your bacterial friends in the digestive system won’t be able to help either. 

*Side note: It’s important to note some insoluble fiber is available for fermentation. You are encouraged to read “Dietary Fibre in Foods: a Review” by Dhringra et al for a better understanding of this concept.

If insoluble dietary fiber is indigestible and non-fermentable, what’s its use?

The key player utilized by your digestive system that works with insoluble dietary fiber is the large intestine. If you’re looking for a great explanation of how the the large intestine works, it can be found here, however a simple breakdown of the mechanism of insoluble dietary fiber in the large intestine will help the get the point across in sufficient detail. According to Johnson W. McRorie Jr. PhD in his work, “Understanding the Physics of Functional Fibers in the Gastrointestinal Tract: An Evidence-Based Approach to Resolving Enduring Misconceptions about Insoluble and Soluble Fiber,” insoluble dietary fiber has some misconceptions surrounding it, mainly its “water-holding capacity.” There are plenty of articles online explaining that insoluble dietary fiber draws-in water to the large intestine and therefore creates a softer and faster-evacuating stool, but this information seems to be incomplete. Insoluble dietary fiber goes through your digestive system about as in-tact as it was after chewing. This means large insoluble dietary fibers have the potential to irritate the lining of the large intestine. As a means of protection, the mechanical agitation of the insoluble dietary fibers promote the lining of the large intestine to release water and mucous. The primary effect of this water and mucous secretion is to protect against abrasion of the lining of the large intestine with the secondary effect of adding moisture to the stool. This helps in both keeping stool hydrated and bulky, leading to a more laxative effect. 

So the more insoluble fiber I eat the better it is for overall digestion?

Not necessarily!

In the same study mentioned in the previous paragraph, finely ground wheat bran actually had a drying effect of the stool in the large intestine, leading to more difficult-to-pass bowel movements and constipation. It seems like the physical size of the insoluble dietary fibers entering the large intestine is the deciding factor on its help or hinderance to overall digestive aid. 

To quote the study, “Large/coarse particles can provide a significant laxative effect/regularity benefit, whereas fine/smooth particles can have a constipating effect…” 

From personal experiences, as well as in-depth discussions with clients, there is anecdotal evidence that the above statement has merit. If you have begun working with a professional from Cornerstone Weight Loss, you have probably been recommended to use Fiber One Original Cereal to aid in hitting your daily recommended dietary fiber marks. However, numerous clients have found that if the dust at the bottom of the cereal bag (you know exactly what that is) is consumed, the likelihood of constipation goes up. Since most of the dietary fiber you get from Fiber One Original Cereal is insoluble, this makes perfect sense in the context of the study mentioned above.


The more knowledge you have of how food affects your body the better. The more astute you become on deciphering what’s right and what’s promoted as right in the weight loss world the more likely you’ll be able to achieve longterm success. Understanding insoluble dietary fiber and the mechanics behind it is important in getting control of how you look; relying on experts can keep you dependent. Dependency means more money down the drain to those who need to keep you ignorant in order to make a profit, and more time you lose sifting through the endless misinformation on weight loss. That being said, it’s important to leave comments and add new information in order to benefit everyone who reads this blog post, so please do so! Also, feel free to email mike@cornerstoneweightloss for any questions or comments you would rather leave off the public forum.

 At Cornerstone Weight Loss we want to help you better understand how food affects your body in a common sense way that will put you in control of how you look. In order to get in touch with a professional who can help tailor your weight loss plan to you, click below, fill out the information, and a member of the Cornerstone Weight Loss team will reach out to you to get the results in weight loss you deserve.

Leave a Reply

Cornerstone Weight Loss is a leading health and nutrition training company that helps people better understand how food affects their body in a common sense way that puts them in control of how they look, forever.
25 N Belcher Rd APT B30
Clearwater, FL 33765

8am to 5pm M-F
(727) 605-1841

To empower you with a clear understanding of how food uniquely affects your body, in a common sense way, that enables you to have complete control over how you look - for life.

Ready To Take Control of Your Weight?

Set yourself up for success with “The 5 Steps to Make Sure You Don’t Kill Your Weight Loss Plans Before They Begin”. Download today!