Gut Microbiome Part 3:
What are Prebiotics?

Last time, we took a 30,000 foot view of the gut microbiome. We explored what it is, why it’s important, and what “healthy” and “unhealthy” gut microbiomes look like, along with the consequences of having an “unhealthy,” dysbiotic gut microbiome. Recall that dysbiosis signifies an imbalance, a tipping point where our microbes are working against us more than with us. The types of microbes in a dysbiotic gut microbiome can be infection-causing, or they can be silent while upping inflammation throughout our body. 

Dysbiosis is tightly linked to “modern” diseases, and much of this comes from the modern diet of industrialized parts of the world, where fast food is king and everything we eat is processed. IBD, IBS, obesity, heart disease, fatty liver disease, allergies, eczema, psoriasis, depression, anxiety, and more can all be traced to contributions from bad microbes treating us badly. What about the good news? What’s the benefit of cultivating a healthy gut microbiome? 

I like analogies. If that wasn’t clear in the last post, it’ll become abundantly clear as we move forward. Let’s go back to the rainforest analogy. Pick anywhere in the forest, and you’ll run out of fingers and toes well before you can count the different species just in eyesight. The gut microbiome is no different. Diversity is good here. Diversity leads to resilience. For example, infections happen, and antibiotics are a necessary evil. Without them, we’d still be dropping death from Montezuma’s revenge, but they can ravage the gut microbiome. Having different species helps protect against catastrophe.

So, a healthy gut microbiome is characterized by diversity of species and resilience of the system as a whole, which is driven largely by the right kind of diversity. Simply put, the more types of “good” bacteria your gut houses, the more different “good” things your gut microbiome is able to help you with. The more types of “good” bacteria you have, the more resilient your gut microbiome will be, helping the system withstand things like stretches of unhealthy eating, antibiotic therapy, infection, and other things that challenge the system.

So, what are prebiotics?

Here’s another analogy. Your gut is a garden, and the main goal of any garden worth its salt is to grow your plant(s) of choice and maximize how much your garden provides while keeping pests away. Prebiotics are like fertilizer for the garden. They nourish your “plants,” affording them a chance to grow quicker than the “weeds.”

Formally, prebiotics are a “substrate that is selectively utilized by host microorganisms, thereby conferring a health benefit.” In plain terms, prebiotics are food for bacteria (or probiotics). 

They take the form of fiber our bodies can’t digest. This means the fiber/prebiotics make it through the stomach and small intestine untouched because our bodies don’t have the tools to break them down. When they get to the colon, they’re available a la carte for beneficial bacteria (or probiotics) like Bifidobacterium and Lactobacillus. These bacteria do have the tools to break down prebiotics into a fuel source, and the result is a postbiotic, a beneficial chemical probiotics make after “digesting” prebiotics that serves us in different ways. An example of a postbiotic is short-chain fatty acids (SCFAs) like butyrate, which is a vital energy source for the cells lining our intestines.

Wonderful! That’s great to hear. But, where do we get prebiotics from?

Plants. That’s the simple answer. Prebiotics come in flavors, and the most well studied flavor is fructans. Fructans include inulin, fructo-oligosaccharides (FOS), and galacto-oligosaccharides (GOS). I mention this because prebiotic supplements on the market will list the “fiber” as one of these things. Noticeable gut health benefits come from as little as 3-5 grams of fiber/prebiotics (though ideal amounts are higher, near 25-30 grams a day).

Here’s a nice table of great dietary sources of fiber:

Prebiotic Type	Primary Food Sources
Inulin & Fructo-oligosaccharides (FOS)	Chicory root, Jerusalem artichokes, garlic, onions, leeks, asparagus, dandelion greens, bananas (especially slightly green)
Galacto-oligosaccharides (GOS)	Legumes (chickpeas, lentils, beans), human breast milk
Beta-Glucans	Oats, barley, mushrooms, seaweed
Resistant Starch	Green bananas, cooked and cooled potatoes, cooked and cooled rice, legumes, whole grains

 

Cool, cool, cool. What’s the catch?

Prebiotics increase the available food for beneficial bacteria, or probiotics. They fertilize the garden so your plants grow well, if you will. As a downstream consequence, they promote gut microbial diversity, which then promotes resilience. They also form a crucial step in the “biotics” pathway, a step that can’t be skipped. Prebiotics -> More Probiotics -> Postbiotics (from the probiotics digesting the prebiotics). That’s all good.

However, in some people, a rapid increase in fiber/prebiotic intake can cause symptoms. Particularly in people with irritable bowel syndrome (IBS), this means a temporary increase in gas, bloating, and abdominal discomfort. People with sensitive guts may take prebiotics and think “what a scam,” rightfully so. You’re taking them to help with symptoms, not worsen them. Knowing the “why” may help you push through. The digestion of prebiotics/fiber is called “fermentation,” and just like fermentation we see in drinks, this means bubbles (gas). That bubbly, gas-producing effect means the gas now takes up space in the gut, causing bloating and pressure, which can be uncomfortable.

It is temporary, and it is a little pain now for more benefit later. Push through for a week or so, and you should be back to normal (and better for it).

So, what’s the takeaway? Give me the cliffnotes. 

Diet is the single most powerful factor influencing the makeup of the gut microbiome and how it can work for you, rather than against you. So, prioritize fiber intake. The cornerstone of gut health and the first step in the “biotics” pathway is a high-fiber diet. The opposite, a low-fiber diet, especially a diet high in ultra-processed foods, effectively “starves” good bacteria/probiotics. Less good bacteria means more room for dysbiotic, or bad bacteria, to grow. The downstream effect of a dysbiotic gut microbiome is the leaky gut phenomenon and ultimately non-stop baseline inflammation, increasing the risk of many of the diseases we fear like heart disease, cancer, and so on.

The gut microbiome is a new frontier, and we learn more every day. The more we understand, as normal people, the more we can make changes that keep our microbes working for us rather than against us. There’s more to come, and by the end, we’ll know enough to be able to optimize our chances at healthy living.

Stop by more often if you learned something. If you want to learn more, read some shorter pieces on our blog or even shorter pieces through our newsletter. Pop your email address in our newsletter sign up for ultra-bite sized education, or read our blog at www.lylahhealth.com for regular bite-sized education. Dr. Bilal Ahmed MD MBA & Zoya Ahmed are great resources too.

See you next time.