Fiber and probiotics: two entirely separate categories of functional foods and supplements you’ll see trending in the gut health and wellness industry, nowadays… for a multitude of research-backed reasons!
But did you know that fiber and probiotics actually work in tandem in many cases, as a dynamic duo, to optimize our gut health?
That’s right – you might start to see foods like flax seeds, chia seeds, psyllium husks, sauerkraut, kimchi, and yogurt in a whole new light by the end of this article.
Read on to learn what’s to love about fiber and probiotics, why you might want to consider a “both-and” approach (versus “either or”), and when fiber and probiotics might NOT be the healthiest add-ins to your gut-healing regimen. (Remember: one size never fits all!)
Disclaimer: This article was written for educational purposes, to complement and enhance – but not replace – medical and nutritional advice from your healthcare providers. Make sure to consult with your healthcare team 1-1 for customized advice tailored to your bio-individual needs.
Table of Contents
What is fiber?
Fiber is a type of indigestible roughage found in plant foods such as fruits, veggies, legumes, nuts, seeds, and whole grains.
It’s renowned for its health benefits which span from gut health to mental health, blood sugar balance, heart health and more.
There are two different types of fiber we can get from food: “soluble” and “insoluble.”
Types of fiber
Soluble fiber
“Soluble” is a fancy way of describing fiber which can dissolve in water. So, soluble fiber dissolves in water and can get consumed (and fermented) by healthy bacteria in our colon, making it “prebiotic”. (1)
- Note that while all prebiotics are fibers, not all fibers are prebiotic.
Soluble fiber has also been shown to delay gastrointestinal (GI) transit time, slow down carbohydrate absorption, reduce cholesterol levels, form gels, and feed (ferment) probiotics in our gut.
Soluble fiber in foods and herbs
Naturally-occurring gums, pectins, mucilage, and sometimes hemicelluloses are the types of soluble fibers you’ll find in foods and even in some fiber supplements. (2)
Foods and herbal sources of soluble fiber include, but aren’t limited to:
- Apples
- Avocado
- Barley
- Chia seeds
- Citrus
- Flax seeds (3)
- Demulcent herbs
- Legumes
- Nopal cactus pads
- Oats and oatmeal
- Okra
- Peas
- Psyllium husks
Insoluble fiber
Insoluble fiber doesn’t dissolve in water. We also don’t have the digestive enzymes to break these fibers down and digest them, so they pass through the intestinal tract and colon still intact.
Instead, this is the type of fiber which adds bulk and roughage to our stools, usually making them bigger, healthier, and easier to pass.
(For context, you want to be aiming for a “Type 3” or “Type 4” on the Bristol Stool Chart – and insoluble fiber from food definitely makes this easier to achieve!
Insoluble fiber in foods
Examples of the most common insoluble fibers you can find in food include cellulose, hemicelluloses, and lignans. (2)
Food sources of insoluble fiber include, but aren’t limited to:
- Flax seeds (3)
- Kiwi (4)
- Wheat bran
- Whole grains (brown rice, wild rice, rye, quinoa, amaranth)
- Raw veggies (lettuce, cucumbers, celery, carrots, fresh peppers)
- Skins of fresh fruit and veggies
Roles and benefits of fiber in the diet
Provides roughage for regularity and detoxification
Foods high in insoluble fiber are a great source of indigestible roughage, which helps support “regularity”.
- In this context, regularity is referring to regular elimination of waste through and out of our gut.
So, insoluble fiber helps us have larger, healthier and more formed bowel movements which are easier to pass… supporting healthy elimination and detoxification.
(Just make sure you’re increasing your fiber intake gradually over a few weeks, versus over a few days, and drinking plenty of water!)
Prebiotic for the gut microbiome
Soluble fibers in food behave differently than insoluble fibers in that soluble fibers are a natural prebiotic, aka FOOD for our gut microbiome which is essentially our unique ecosystem of probiotics in our gut. (1)
Helps support blood sugar regulation
Both soluble and insoluble fibers from food and supplements have been shown to help slow down and buffer the breakdown of carbohydrates into sugars, and the absorption of glucose into the cells.
This is key for everyone, but especially for folks with diabetes/prediabetes, and/or polycystic ovarian syndrome (PCOS).
Aids in satiety and fullness
Fibers from food and supplements add bulk without adding calories.
That’s why eating fiber-rich foods generally helps us to feel fuller and more satiated for longer.
In most cases, increased satiety helps us to limit our food consumption and reduce the likelihood of overeating, to a certain extent.
May help reduce cholesterol
Foods and supplements containing soluble fiber are well known to help reduce cholesterol levels. (2, 4)How it works:
- According to a 2023 review by ACS Omega, first and foremost, due to its satiety-promoting effects, healthier portions generally contribute to healthier cholesterol levels. (2)
- On another level, soluble fiber has been shown to help bind bile acids, reducing their reabsorption into enterohepatic circulation while simultaneously enhancing the excretion of cholesterol-containing bile in stools. (2)
- Finally, the prebiotic butyrate-producing activity of prebiotic soluble fibers may help reduce cholesterol indirectly by reducing inflammation.
For all of the above reasons, this may explain why including at least 10 grams/day of soluble fiber has been shown to reduce the risk of heart disease by 14% while also reducing the risk of coronary death by 27%, with less side effects compared to statin medications. (2)
Helps manage and reduce constipation and IBS
If you’re hoping to reduce/manage symptoms of constipation, you may benefit from a high-fiber diet or fiber supplements – as long as your constipation isn’t caused by methane-type small intestinal bacterial overgrowth (SIBO).
That’s because the insoluble fiber has been shown to decrease stool transit time which, in most healthy individuals, is between ~12-24 hours.
More specifically, supplementing with ~10 grams/day of fiber-rich psyllium for just 4 weeks was shown to be very effective at reducing constipation in adults, according to a 2022 study. (5)
On the other hand, soluble fiber seems to be better tolerated by people with diarrhea-predominant irritable bowel syndrome (IBS-D) and may help increase transit time for people prone to diarrhea. (6) This may be due to the prebiotic properties in soluble fibers.
How much do we need?
According to the United States Department of Agriculture’s Dietary Guidelines for Americans (2020-2025), most healthy adults need about 20 to 35 grams of fiber (or about 14 grams of fiber for every 1,000 calories consumed) per day. (7)
More specifically…
- Most healthy adult females need ~20-25 grams of fiber per day
- Most healthy adult males need ~25-35 grams of fiber per day
While it’s worth noting that over 90% of Americans aren’t getting enough fiber in their diet (7), let’s shift gears and talk about probiotics.
What are probiotics?
Probiotics are health-benefiting microbes which are part of our microbiome – or ecosystem of microbes which live in our body (mostly in the gut).
(Fun fact: the latest research has revealed we have at least as many microbes in our body as we do human cells… so, over 35 trillion of each!) (8)
We need probiotic microbes as much as they need us as their host. This is a mutually beneficial or “symbiotic” relationship.
But it doesn’t stop there!
Probiotic microbes are also abundant in many types of lacto-fermented functional foods and probiotic supplements.
Probiotic foods
Examples of probiotic-rich foods include, but aren’t limited to:
- Raw sauerkraut
- Raw, vinegar-free pickles
- Raw, vinegar-free kimchi
- Miso
- Yogurt
- Yakult
- Kefir
- Kombucha
Supplements
Probiotic strains can be isolated and extracted into supplement form, whether as liquid or capsules. There are hundreds of thousands of different probiotic supplements on the market.
While one size never fits all, and no two probiotic supplements are the same, some of the most well-researched types of probiotic supplements for human health may include various strains of Lactobacillus and/or Bifidobacterium.
Roles and benefits of probiotics for gut health
As Hippocrates once said, “All disease begins in the gut” – so wouldn’t it make sense that healing and good health ALSO begin in the gut?!
That being said, our gut is the cornerstone and a gateway into pretty much every facet of our health.
And since probiotics live mostly in our gut, they come with quite the laundry list of health benefits, including but not limited to:
- Support healthy digestion and nutrient absorption (9)
- Help support and optimize immune function (9)
- Support heart health by improving and optimizing blood pressure and cholesterol levels (9)
- Improve bowel function (9)
- Support healthy skin (9)
- Help optimize hormone balance (9)
- Reduce inflammation by making and releasing substances called short-chain fatty acids, aka “post-biotics” like butyrate in our gut (9)
- Help regulate and optimize metabolism of nutrients into energy (9, 10)
- Improve mental health and cognition (11)
Recommended reading: How to Increase Butyrate in Your Gut (Directly and Indirectly)
What do fiber and probiotics have in common?
There’s a lot of overlap between fiber and probiotics, in functional foods and in supplement form, when it comes to their potential health benefits.
Both fiber and probiotics (in their own unique ways) are generally well known to support a healthy gut by improving digestion and regularity, improving heart health by reducing/optimizing blood pressure and cholesterol, and potentially reducing inflammation in many cases.
However, it’s important to keep in mind that fiber and probiotics are two entirely separate types of gut health allies which have distinctly different (but both very important) roles in our body.
Fiber vs. probiotics: A comparison
How are they different?
Fibers (whether soluble or insoluble) are constituents which we cannot digest or break down.
Both soluble and insoluble fiber are found exclusively in plant foods, and they often act as prebiotics which FEED the probiotics (healthy bacteria) in our body and in the creation of lacto-fermented foods.
Probiotics, on the other hand, are LIVE organisms which live in us and on us. They benefit our health by consuming the prebiotic soluble fibers and polyphenols found in plant foods/herbs, fermenting and making/releasing short-chain fatty acids (like butyrate) as a bi-product.
The short-chain fatty acids or “post-biotics” are the potent anti-inflammatory healing substances which come from the combination of prebiotic fibers + probiotic microbes in our gut, and they are what make probiotics so darn good for us.
Which is better to start with?
As I mentioned earlier on, I wouldn’t go out of your way to try and choose between fiber and probiotics but rather to integrate them synergistically if you’re looking to support and optimize gut health.
There are, however, certain scenarios in which you may be better off leaning on one or the other.
(As always, this ultimately varies case-by-case depending on your bio-individuality. But below are some general clinical considerations worth checking out!)
Fiber vs. probiotics for constipation?
If you’re dealing with chronic constipation or constipation-predominant irritable bowel syndrome (IBS), based on research and my clinical experience in private practice, you may want to try prioritizing FIBER FIRST, before trying probiotics.
On that note, if you suffer from symptoms of IBS and notice you don’t tolerate probiotic foods/supplements, keep reading!
Fiber vs. probiotics for SIBO?
When it comes to small intestinal bacterial overgrowth (SIBO), people don’t always tolerate fiber OR probiotics in my experience.
(That’s right… feeling worse on a high-fiber diet and/or having adverse reactions to probiotics are actually two tell-tale signs of SIBO versus IBS!)
However, you may still want to consider focusing on “fiber diversity” (aka a variety of natural prebiotic foods) from cooked low FODMAP veggies and small amounts of low FODMAP fruits in your diet, as tolerated.
TLDR: Focusing on fiber diversity may generally be more helpful and better tolerated than probiotics of any kind, if you have SIBO.
(This is based on what I see often in my private gut health nutrition practice, and it overlaps a lot with fiber versus probiotics when it comes to histamine intolerance too.)
Which is better for histamine intolerance?
If you have a histamine intolerance, integrating a variety of well-tolerated fiber-rich, low-histamine foods may be better for you than probiotic foods.
That’s because fermented probiotic foods are all naturally high in histamine.
On the other hand, probiotic supplements may or may not be better tolerated than probiotic FOODS and fiber supplements in some cases of histamine intolerance.
Fiber vs. probiotics for IBD?
Inflammatory bowel disease (IBD) is a type of autoimmune disorder in which the lining of your gut is chronically inflamed.
In many cases of IBD you may actually experience an intolerance to fiber and roughage, so leaning on probiotics FIRST before fiber would be a better option in this case.
Either way, make sure to consult with your treatment team for customized diet and supplement recommendations for all medical conditions but especially IBD!
Recommended reading: Low Fiber Foods List PDF [Free Download]
Learn more
Did you know I’ve been interviewed by media outlets as an expert on fiber-rich foods and supplements? Feel free to check these articles out to learn more about fiber!
- 15 Fiber-Filled Snacks That Boost Your Gut and Give You All-Day Energy
- 7 Foods To Relieve Constipation, According To Experts
- ColonBroom Review (2024)
- 9 Ways Eating Kiwi Benefits the Body, According to Registered Dietitians
- Is Increased Fiber Curing Your Constipation or Causing It? Here’s Exactly How To Tell
The bottom line
Both fiber and probiotics in functional foods and supplements offer a wide array of research-backed health benefits, especially when it comes to gut health.
They have very different mechanisms of action but they generally work best when combined versus taken in isolation.
That’s because many fiber-rich foods act as prebiotics, supporting the natural growth of probiotics in our gut while insoluble fiber-rich foods are able to add bulk to stools, making them healthier and easier to pass.
At the end of the day, we usually benefit from (and need) both fiber and probiotics (in most cases) in our diet.
But it’s best not to add both fiber and probiotics into your regimen at the same time or to add too much too fast of either option
When it comes to fiber, it’s important to increase your fiber intake gradually over a few weeks (and increase water intake too) versus exponentially increasing fiber intake over a few days to prevent adverse reactions like bloating, gas, or impaction.
The same goes for probiotics; it’s better to introduce them gradually so you don’t experience any kind of “die-off” or other adverse reactions.
Some people prefer food sources of fiber and probiotics, while other people prefer the convenience of supplements.
If you’re dealing with special clinical considerations like constipation, SIBO, histamine intolerance and/or IBD should consult your healthcare team for customized recommendations.
Next steps
Are you looking for expert guidance on your journey to better gut health? Apply to work with me 1-1 if you live in the U.S. HERE and someone from my team will be in touch, if we might be a great match!
XX – Jenna
