Author: Trish Shea R.D.
There is More to be Said About Fiber
Now that we have gotten the basics of fiber down (click here to read our first blog on fiber), let’s explore a bit deeper. There is so much to be said about fiber and its profound impact on our health and longevity.
- Fiber is a type of carbohydrate that can only be found in plant foods.
- Our bodies lack the enzymes necessary to digest dietary fiber. So instead, bacteria in the gut microbiome metabolize fiber into short-chain fatty acids, which are then absorbed by the body.
- Short-chain fatty acids have a significant, positive impact on multiple aspects of human health, including the health of the microbiome (arguably the foundation of health).
The healthiest, longest-lived populations still left on this planet, which are also called Blue Zones, eat a diet that is mostly made up of whole, plant-based foods. It is no coincidence that these groups of people have a much better quality of life (largely without chronic disease) and live longer (upwards of 100 years old), healthier lives than their Western counterparts.
Not All Fiber is the Same
Dietary fiber is a complex group of substances that can be categorized according to their source, solubility, fermentability (how effectively bacteria metabolize them), and physiological effects.
Different forms of dietary fiber include:
- Non-starch polysaccharides (hemicellulose): Found in cereal grains; present in both soluble and insoluble forms
- Pectin: water-soluble polysaccharide; highest amounts found in fruit and to a lesser degree in vegetables, legumes, and nuts
- B-glucans: non-starch polysaccharide, generally soluble; highest amounts found in barley and oats
- Cellulose: major component of plant cell walls; found in grains, fruits, and to a lesser degree in vegetables and nuts
- Lignin: Found in foods with a woody component aka celery and the outer layer of cereal grains (The outer layer is the bran, which is the part that is removed during processing, but remains intact in whole grains)
We could keep going, but you get the drift.
The important thing to know is that there are many different types of fiber (more than we can count) and each type has different physiological properties. This is why it is so important to eat a diet rich in a variety of plant foods.
Wait, why is it important to eat different types of fiber?
Each plant food has its own mix of different types of fiber that feeds its own unique set of microbes housed in the gut. This allows our microbes not only to grow, but to thrive. And when our microbes thrive, our health thrives.
Why can’t I just go out and buy a fiber supplement instead?
When you take a synthesized fiber supplement, it usually contains only one type of fiber, let’s say psyllium husk. Besides missing out on all of the vitamins, minerals, and phytochemicals that are found in whole plant foods, you are not getting the variety of different types of fiber that is key for a healthy gut.
The same can be said if you ate kale all day long. Remember: Eating a diversity of plants is the number 1 determinant of a healthy gut. There is no sidestepping this one folks!
Soluble vs Insoluble Fiber
When fiber is categorized according to its solubility, it can be broken down into two broad groups: soluble and insoluble fiber.
What Is Soluble Fiber?
Soluble fiber absorbs water during digestion, which forms a gel. This increases the viscosity of the contents of the GI tract, adding lubrication to the stool. It has also been shown to decrease glucose levels and cholesterol in the blood. Soluble fiber can be found in foods like oats, fruit, vegetables, and legumes.
What Is Insoluble Fiber?
On the other hand, insoluble fiber remains unchanged during digestion. It adds bulk to the stool and helps with bowel regularity and prevention of constipation. Insoluble fiber is found in foods like wheat, brown rice, legumes, and vegetables.
Fiber-containing foods have different proportions of both soluble and insoluble fibers, so it is important to eat a variety of these foods.
Prebiotics + Probiotics = Postbiotics
We live in an age where you can go to your local grocery store and buy probiotic supplements, but there is much more to the story of gut health than purchasing an over-the-counter remedy.
Let’s break this equation down.
Prebiotics are the indigestible food component that benefits the host organism by stimulating growth and activity of beneficial bacteria, thereby improving the health of the host (gut health and therefore overall health).
In other words, fiber promotes the growth of beneficial bacteria in our gut, which play a major role in gut health. The caveat is that all prebiotics are fiber, but not all fiber is considered to be a prebiotic.
For instance, most soluble fiber is prebiotic, while most insoluble fiber is not. Resistant starch also meets the criteria for being a prebiotic, although it is technically not fiber. Resistant starch is found in foods like oats, buckwheat, rice, potatoes, and legumes.
Probiotics are living cultures of bacteria (single species or mixed) that may be applied to humans and in doing so will have a beneficial effect on the microbiome by improving the properties of the gut microbes already residing there. In terms of the above equation, we are simply referring to probiotics as the living bacteria that benefit us humans.
Postbiotics are the end-products of fiber metabolism by gut microbes, also called short-chain fatty acids.
So essentially this equation means the prebiotics (the things that feed the good bacteria in our gut, such as fiber) combined with probiotics (the living bacteria that benefit us) produces postbiotics aka short-chain fatty acids (SCFAs).
Why is this important to understand?
If we want to take advantage of the countless health benefits that SCFAs offer, see our first blog article on fiber for a list of health benefits.
We need to be consuming more fiber, especially prebiotic fiber and resistant starches, which means that we need to be eating more plant foods. We cannot say it enough, eating a diet that is rich in a variety of whole plant-based foods matters big time!
Your Plan for Eating More Fiber
Great, so we get it, we need to eat more fiber in the form of whole plant-based foods. But… how much fiber is really enough?
The good news is, there's no need to start counting the grams of fiber in everything that you eat.
There is a much simpler solution: Try to maximize plant diversity with every meal.
A general guideline is to strive to eat at least 30 different plants per week (recommendation from the book “Fiber Fueled” by Dr. Will Bulsiewicz, which we highly suggest that you read!), but the more the better.
If you suffer from bloating, gas, and other uncomfortable symptoms from eating things like beans, raw vegetables, and other plant foods, you are in luck.
The key here is to start low and go slow with fiber containing plant foods.
Let’s add some context to this.
The presence of these symptoms means that our gut has been damaged and the bacteria in it are missing the enzymes necessary to process carbohydrates and the fiber contained within them.
That’s right—the microbes in our gut have way more digestive enzymes (we are referring to glycoside hydrolases specifically) than we do, which is why we rely on them to do much of the heavy lifting when it comes to processing complex carbs.
The good news here is that you can heal your gut. The gut is like a muscle, the more you exercise it by adding fiber rich foods into your diet, the greater your capacity will be to digest those foods, because enzyme levels will start to increase over time.
What you need to remember is to introduce fiber rich foods slowly enough that you will start to make your gut stronger without making yourself too uncomfortable in the process.
This is the simplest way we can break this down:
Eating a diversity of plants = Getting a variety of different types of fiber into the diet = Increased growth of healthy bacteria species = A healthy microbiome = Increased production of short-chain fatty acids = Better overall health!
It has been shown that the health of the microbiome is the key that unlocks a healthy, long life. What makes for a healthy microbiome? Yes, you guessed it, a diversity of plants in the diet and all of the different types of fiber that come along with it.
- Bulsiewicz, Will. Fiber Fueled: The Plant-Based Gut Health Program for Losing Weight, Restoring Your Health, and Optimizing Your Microbiome. Penguin Random House, 2020.
- Carlson, Justin L., et al. "Health effects and sources of prebiotic dietary fiber." Current developments in nutrition 2.3 (2018): nzy005.
- Fuller, Stacey, et al. "New horizons for the study of dietary fiber and health: a review." Plant foods for human nutrition 71.1 (2016): 1-12.
- General Information on Fiber. Harvard T.H. Chan School of Public Health, The President and Fellows of Harvard College, https://www.hsph.harvard.edu/nutritionsource/carbohydrates/ fiber/.
- Mudgil, Deepak, and Sheweta Barak. "Composition, properties and health benefits of indigestiblecarbohydrate polymers as dietary fiber: A review." International journal of biological macromolecules 61 (2013): 1-6.
- Sivaprakasam, Sathish, Puttur D. Prasad, and Nagendra Singh. "Benefits of short-chain fatty acids and their receptors in inflammation and carcinogenesis." Pharmacology & therapeutics 164 (2016): 144-151.