Fiber and the Gut Microbiome: Pre, Pro, and Postbiotics

Eating a diet that is packed with fiber is essential to a healthy lifestyle, gut health, and our immune system; out gut microbiome thrives on this fiber! Yet across the western world, our dietary fiber intake is decreasing. Research now shows that for the majority of people, the level of fiber they consume falls significantly below the recommended daily intake of 28-35g. 


Fiber is found across a wide range of whole plant foods, but primarily within vegetables, fruits, whole grains, seeds and legumes. It is therefore crucial to incorporate these into our diets. Unlike other macronutrients in food like fats and proteins, fiber is not broken down, absorbed, or digested by our body and digestive enzymes . Instead, it effectively passes through the body intact until it reaches the large intestine or colon. There the gut microbiome breaks some of it down, digesting it and using it to fuel itself, our colonic wall and other important processes throughout the body.

Fiber is powerful fuel for your gut microbiome.
Plants are the best source of fiber!


There are over 100 types of fibers identified in plant foods, but scientists have broken them down into two broad groups:


  • Soluble Fiber

This form of fiber dissolves in water and helps to lower blood cholesterol and glucose levels.


  • Insoluble Fiber

This type of fiber promotes digestive movement and increases stool bulk.


Fiber is also crucial to supporting a healthy gut microbiome. Our good gut bacteria feeds off it, allowing it to thrive. When we do not consume enough dietary fiber, our microbiota begins to break down the mucus layer within the intestines as a source of energy. This is very bad. The integrity of the mucus layer and intestinal wall is essential to controlling inflammation, digestive issues and even chronic conditions such as autoimmune disease and colon cancer. 

Our gut Microbiome is a constantly changing system, so optimizing our diet and lifestyle can help to change it for the better. The development of our gut microbiome relies on fiber, which improves our gut in three core areas:




Scientifically, prebiotics foods are:

  • resistant to gastric acidity, hydrolysis by human enzymes, and gastrointestinal absorption
  • fermented by the gut microflora
  • Stimulate the growth and activity of gut microflora associated with health
Prebiotic-rich meal for your gut microbiome.
A meal full of powerful prebiotics for your microbiome.

In short, prebiotics are the foods that power the microbes in our gut and cannot be digested by the body. The primary source of prebiotic molecules is from a plant-based diet. Each microbial community is basically in charge of digesting different groups of fiber. The wider the variety of fibers we feed our gut microbes, the more we  ensure that they are thriving. Failure to feed a subset of microbes – like by avoiding grains or certain vegetables –  means they will not have the resources to replicate or serve their essential functions. Ensuring your diet is packed with prebiotics helps to encourage the growth of these positive microbes. So ensuring you incorporate plenty of fruit, vegetables, and whole grains into your diet can significantly boost your gut health.


Prebiotics have also been shown to help to lower obesity, lower the risk of diabetes, and decrease the risk of several chronic diseases.




Probiotics, according to the World Health Organization, are live microorganisms that when consumed  in “adequate amounts, confer a health benefit on the host”. These are essentially live beneficial microbes that we add directly to our gut to start providing us with a wide range of benefits.


Consuming probiotics can help to boost the number of healthy microbiomes in our gut, this in turn promotes microbial diversity and helps keep pathogenic microbes under control. 


Probiotics and the chemicals they produce are responsible for regulating many of our body functions. They can help with digestion and with  boosting our immune systems. Probiotics are regularly found in fermented foods such as tempeh, miso paste, yogurt, sauerkraut, kimchi and in many other culturally diverse foods throughout the world. It’s important to note that raw plant foods such as fruits and vegetables are living foods and also carry probiotics from the soil.




When your body consumes prebiotics and the microbes in your gut digest them and use them for their own energy, they produce byproduct molecules which are known as metabolites. These molecules, alongside dead cells, are known as postbiotics. These provide the body with a range of benefits that protect your health, including:


  • Vitamin B and K
  • Short-chain fatty acids that maintain gut lining and support metabolism
  • Antimicrobial molecules
  • Bacterial fragments that boost the immune system


Ensuring your body is getting enough pre- and probiotics will help your microbiome create the postbiotics it needs for a healthy gut.

She is eating great food for her gut microbiome.
This lady loves her fiber-rich snacks!

How to get more fiber into your diet


Incorporating more fiber into your diet is essential to keeping you healthy and for promoting good gut health. Ensuring that we eat enough can be tough, though, so here are some tips to help you get your fiber on!


Eat your greens


One of the most effective ways to boost your fiber intake is to ensure that you are eating a diet heavy in plant-based foods. Adding more fruit and vegetables to your meals will increase your fiber consumption and provide you with a wide range of other benefits too.


Eat seasonally


Another popular method of increasing your fiber intake and keeping your gut microbiome diverse is to eat those greens that are in season. Not only does this ensure you get the freshest ingredients possible, but they are often more affordable too.


Consume less processed foods


Processed foods typically contain less fiber as the processing strips away a lot of it. Try to find the most unprocessed food you can – I recommend the produce aisle and showing along the outer grocery aisles!

Legumes are wonderful for your gut microbiome.
Legumes are a fantastic source of fiber and are filled with tons of nutrients.

Add your beans/legumes/pulses


While fruit and vegetables are an essential part of any diet, don’t forget to include legumes such as beans and lentils. These are a fantastic source of fiber and are filled with tons of nutrients.




Studies suggest that consuming at least 30 plant foods per week is associated with increased microbial diversity. The more diverse your gut Microbiome, the more optimized your body’s functions will be!


Wrapping Up


Adding these ingredients into your diet can help you to significantly increase your fiber intake. While there are some fiber supplements available on the market,  you should try to skip these in favor of fresh and natural ingredients, as they can provide greater benefits. 


While eating more fiber is essential, you should do it gradually and at your own pace. Increasing your fiber intake too rapidly can cause bloating and abdominal discomfort. Think of your gut Microbiome like a very large muscle that needs to be trained! It requires patience and a gradual increase in activity to get results; working it out too quickly leads to injury. Along with that gradual increase in fiber, drink more water to ensure things are running smoothly. Water and fiber work together in the gut, and one without the other is a recipe for extremes of constipation or diarrhea.


To optimize your Gut Health, download Dr. Mendez’s Gut Health Guide! If you are looking for support to help improve your diet and boost your gut microbiome, then get in touch today or register to make an appointment to discover how Doctor Méndez can help you to optimize your health.



Desai MS, Seekatz AM, Koropatkin NM, et al. A Dietary Fiber-Deprived Gut Microbiota Degrades the Colonic Mucus Barrier and Enhances Pathogen Susceptibility. Cell. 2016;167(5):1339-1353.e21. doi:10.1016/j.cell.2016.10.043


Berry, S.E., Valdes, A.M., Drew, D.A. et al. Human postprandial responses to food and potential for precision nutrition. Nat Med 26, 964–973 (2020).


Shah BR, Li B, Al Sabbah H, Xu W, Mráz J. Effects of prebiotic dietary fibers and probiotics on human health: With special focus on recent advancement in their encapsulated formulations. Trends Food Sci Technol. 2020;102:178-192. doi:10.1016/j.tifs.2020.06.010


Hill C, Guarner F, Reid G, Gibson GR, Merenstein DJ, Pot B, Morelli L, Canani RB, Flint HJ, Salminen S, Calder PC, Sanders ME. Expert consensus document. The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic. Nat Rev Gastroenterol Hepatol. 2014 Aug;11(8):506-14. doi: 10.1038/nrgastro.2014.66. Epub 2014 Jun 10. PMID: 24912386.


Wang, Y. and Shurtleff, D., 2021. [online] Available at: <> [Accessed 17 May 2021].


Patel RM, Denning PW. Therapeutic use of prebiotics, probiotics, and postbiotics to prevent necrotizing enterocolitis: what is the current evidence?. Clin Perinatol. 2013;40(1):11-25. doi:10.1016/j.clp.2012.12.002

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