Hello and welcome back to the Pelvic Empowerment IBS Series!
My name is Tori and I am doctor of physical therapy who specializes in pelvic dysfunction,
which means I treat things that can go wrong around the pelvis—including bowel dysfunction.
In May of this year, I decided to try my best to unpack what I have learned about IBS in a
video series, and today I wanted to add a fifth installment building on my previous
videos that breaks down the difference between soluble and insoluble fiber.
Today, we’ll first discuss an overview of fiber in general before diving into
the differences between soluble and insoluble fiber, we’ll then do a quick review of how your
digestive system works—especially the gastrocolic reflex and peristalsis—and
we’ll end by talking about how soluble and insoluble fiber affect diarrhea-dominant,
constipation domination, and mixed IBS symptoms.
As always, you can check below for timestamps and links to all
of the previous videos in this series!
Let’s get started by talking about fiber.
Fiber is a type of carbohydrate found only in plant-based foods that is not digestible by
humans. We can’t digest it because we don’t make the right kinds of enzymes necessary to break it
down. Which means any kind of fiber—soluble or insoluble—is NOT broken down and absorbed
in our digestive tracts. Instead, fiber passes through our digestive system relatively unscathed.
The main difference between soluble and insoluble fiber is their relationship
with water. Soluble fiber attracts and absorbs water—which turns it into a mushy,
gel-like substance as it moves through our intestines. Think about what happens when you
add water to oatmeal, and use that visual to imagine soluble fiber absorbing water
and swelling into a mushy-toothpasty-gel-like substance as it moves through your intestines.
Insoluble fiber, on the other hand, doesn’t absorb water. In fact, it repels water—which means it
passes through our digestive system close to its original form. Think about what happens when you
add water to celery—close to nothing about the celery changes. I think we can all think of
personal experiences that have demonstrated this phenomenon—such as eating high fiber veggies like
leafy green ruffage or corn—and then seeing undigested bits of these foods in our poop.
Most plant-based foods contain a combination of soluble and insoluble
fiber—they’re just usually richer in one type more than the other.
When we think of fiber, we’re usually thinking of foods that are high in
insoluble fiber—foods that are rough, stringy, or have tough skin like greens, veggies, nuts,
seeds, and legumes are all foods that contain a high concentration of insoluble fiber.
Soluble fiber, on the other hand, is found in high concentrations in foods that we
commonly consider to be “starches,” such as rice, potatoes, and yams.
Now that we’ve discussed an overview of fiber, we need to understand how our GI system works before
making sense of how soluble and insoluble fiber can be used to manage IBS symptoms.
In the first installment of this series
we reviewed how the digestive system works and introduced the gastrocolic
reflex. I want to review that again, and really focus on intestinal movement.
Recall that, if we follow food from mouth to bowel movement, it goes in your mouth, you chew it
and swallow it, it then moves down your esophagus, into your stomach, through your small intestines,
then your large intestines, then into your rectum and finally, out of your anus as a bowel movement.
But what happens specifically in your intestines? They move! They rhythmically contract and relax to
propel food and eventually waste through them. That is how waste ends up in your
rectum and eventually in your toilet. This rhythmic contraction is called peristalsis,
and it looks very much like when a snake eats a mouse.
Remember that this intestinal muscular movement is not under your voluntary control—much like
you don’t have voluntary control over your heart muscles. Instead, there is a reflex, called the
gastrocolic reflex, that stimulates peristalsis (or that rhythmic contraction of the intestines).
Now, let’s really zoom into that intestinal movement. I want you to imagine your intestines as
a singular, muscular tube. Regular, healthy bowel movements depend on adequate filling of that tube,
and a soft consistency of the food/stool mixture inside of that tube. When the tube is adequately
filled, the muscles are stimulated via stretch to perform peristalsis. When the tube is adequately
filled with a soft food/stool mixture, those muscles have something easy to “grip” as they
rhythmically contract—resulting in a regular, healthy bowel movement.
Why is this important to review? Because understanding the gastrocolic reflex and
peristalsis will make sense of fiber and how it can soothe and control IBS
symptoms! With this review under our belts, we can now discuss soluble fiber and IBS.
IBS presents in three ways: diarrhea-dominant,
constipation-dominant, or mixed. The incredible thing about soluble fiber is that, in theory,
it should normalize both diarrhea AND constipation. I want you to understand why.
Let’s first break down why soluble fiber would help diarrhea. When someone has
diarrhea, the intestinal muscles have nothing to “grip” during peristalsis,
and you end up with a super fast transit time and explosive bowel movements.
Recall that soluble fiber attracts water—this means it absorbs excess liquid in the intestines,
replacing diarrhea with that thick mushy-toothpasty-gel-like substance we
discussed earlier. This substance keeps the intestinal muscular tube gently stretched,
and gives those muscles something easy to “grip” as they rhythmically contract.
This slows down the otherwise rapid transit time associated with diarrhea,
and prevents the explosive bowel movements associated with diarrhea.
That makes sense, but why would soluble fiber also help with constipation? When
someone is constipated, the intestinal muscles are often clenched around dry,
hard, impacted stool, and you end up with a slow transit time, bloating, and hard bowel movements.
In this scenario, recall again that soluble fiber attracts water—so that
thick mushy-toothpasty-gel-like substance would soften, break apart, and push through dry,
hard, impacted stool. It would also give the intestinal muscular tube that same gentle stretch,
giving the muscles something much easier to “grip” than hard, dry stool as they
rhythmically contract, resulting in a faster transit time and softer bowel movements.
So, soluble fiber is great. But what about insoluble fiber?
There is a catch with insoluble fiber. On one hand, insoluble fiber is incredibly good
for you. Some of the all-time healthiest foods are high in insoluble fiber. On the
other hand, insoluble fiber is a powerful gastrocolic reflex stimulant—much like fat,
which we discussed in great detail in the second installment of this series.
So, what does that mean for someone trying to manage her IBS symptoms through diet? I
will explain that in detail in the next installment of this series,
where we will tie in EVERYTHING that we’ve discussed in the past five
installments and outline specific dietary considerations for IBS symptom management!
On that note, thank you all so, so much for watching! I am so honored
and excited to be creating this series for you—thank you from the bottom of
my heart for watching, commenting, and requesting.
As I mentioned, the next video in this series will hopefully wrap the past five videos into
a neat little bow and deep dive into IBS symptom management through diet. I also
intend to make videos in this series that cover IBS and its relationship to FODMAPs,
SIBO, anxiety, sleep, and exercise as well as other treatment options for
IBS like pharmaceuticals—linzess and trulance especially—fecal transplants, and alternative
medicine. But if you have a different IBS-related topic you want me to add to the series, please let
me know in the comments below! I do try really hard to read and respond to all of my comments.
Please, if you found this video helpful, give it a thumbs up, share it, and,
finally, subscribe to my channel for more content surrounding both pelvic things and life things.
Don’t forget to check meowt on instagram, and thank you so much again for watching.
Have a wonderful rest of your day, and I’ll see you in the next video, bye!