• Gavin Guard, Medical Director

Why more fiber is NOT always better

Updated: Jan 21

Why is everyone talking about gut health? It seems like it has become the new fad in the health and fitness industry. Of course, a lot of good things have come out of focusing on the gut as a main driver of chronic diseases and symptoms. However, I think some clinicians have gone a little too far with their overzealous approach of focusing on the gut.

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The gut has a bidirectional relationship with the rest of the body. This means that gut health has an impact on the body’s health and vice versa. The majority of the brain’s output feeds into the vagus nerve. This nerve communicates with the whole digestive tract, mediating gut function and motility. In return, the gut has a profound input into the vagus nerve which then feeds back to the brain.

Yes, the microbiome is very important. However, if the host of the microbiome (the body) is not healthy, then eating more fiber in the hopes of “feeding the microbiome” doesn’t really matter.

Maybe it would be a better approach to address not only gut and digestive health, but also the overall health of the host. This means things like the appropriate amount of exercise, adequate quantity AND quality of sleep, limiting blue light exposure, stress management, and engaging in community. Whilst addressing these topics, we can also serve the health of the microbiome and digestive tract function.

We also see this gut-centered type of thinking with those wanting to eat like other people groups. Take the Hadza for example, a tribe of indigenous people living in Tanzania. Many people point to this group as a great example of what Americans should be eating. The Hadza eat a lot of fiber-rich tubers and plants- up to 100-150 grams of fiber per day! Now, the average American is probably getting maybe a third of this. If we were to start eating like this, bad consequences would occur to our gut- we would probably need to invest in Charmin Ultra Plus toilet paper.


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Many functional medicine clinicians point to the Hadza as a great example of what our diet should look like. But is this thinking skewed? I think so. The Hadza have been eating like this for a long time and have probably evolved adaptations to allow them to handle this larger bolus of fiber. They haven’t been exposed to multiple doses of antibiotics or c-sections at birth. Therefore, their microbiome is surely different than that of the standard American.

My point here is that there are two drastically different gut ecosystems here- one of the Hadza and the other of us standard Americans. What if you were to go to Amazon rainforest and see all the beautiful and diverse array of plants and wildlife? You might think to yourself, “a lot of rain is the cause for this awesome ecosystem.” However, what if it were to rain as much as it does in the rainforest in let’s say, the desert in Arizona. Surely this would massive landslides, flash floods, and destruction.

These two different ecosystems require different amounts of rain just how different people require different amounts of fiber and microbiome “feeding”. Flooding a person with an overgrowth of bacteria can lead to even more problems. This is because bacteria in our gut ferment (metabolize) fiber into byproducts that they and our body can use to fuel certain activities. More fiber equates to more bacteria and their byproducts, which is a problem for someone who already has an overgrowth.

Be careful next time someone tells you that you need to eat more fiber in order to feed your microbiome. Work with an experienced clinician to do the appropriate assessment and testing to see if you could benefit from a “trimming” approach to your microbiome instead.

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