I Can Feel it in my Gut

Just like the fashion world, the science world has trends.  What are the hot fashion trends right now?  You’ll have to ask Nate…  As for the latest craze in science, it’s gut bacteria. 

First, a short review on bacteria.  Bacteria are about a tenth of the size of human cells and are found everywhere in the world, including inside you and on your skin. In fact, you have more bacteria cells in and on you than you have human cells (estimates vary and go up to a ratio of 10:1 (1)).

We all know some of these bacteria can be harmful to humans.  However, some bacteria can actually be beneficial.  It’s this latter symbiotic relationship which is what science has begun to focus on.

The majority of the bacteria located on you or in you, are found in the gut.  More specifically, most bacteria (10-100 trillion) are found in the large intestine (1).  Not too long ago, we used to think all the valuable digestion and absorption of nutrients had already occurred by the time food reached your large intestine.  Now we know that’s only partly true. In the large intestine, some of the food that you weren’t able to digest actually gets digested by bacteria.

In this process of breaking down food, bacteria produce various products that can actually be beneficial to human health.  For example, gut bacteria produce short chain fatty acids which the cells of our large intestine can use as energy (2).

Researchers are also looking at how the byproducts from gut bacteria may help exercise performance.  You may remember a popular media article suggesting gut bacteria help make better athletes, which led to the term “poop doping”.  While fitter individuals do have greater gut bacteria “health” (3), the article was a little too speculative, as researchers don’t know whether one (healthy gut bacteria) causes the other (high fitness level).

No study to date has determined a mechanism for how gut bacteria can directly impact exercise performance.  That being said, gut bacteria may indirectly influence exercise performance.  For example, gut bacteria produce signaling molecules that assist with reducing inflammation and improving immune function (2).  This could help with recovery and overall health, leading to better performance (3).

So, what does “healthy” gut bacteria look like?  At this point, no research has found the optimal species of bacteria or distribution of bacteria (3).  Instead, a “healthy” gut simply has a diversity of bacteria types (4). This idea can be hard to grasp but can be better understood when thinking like an ecologist.  Maybe you’ve seen the video of what happened in Yellowstone National Park when wolves were reintroduced.  To summarize, when wolves were reintroduced (an increase in diversity), the overall health of the ecosystem improved.  The same happens in the human body. 

While a number of things influence diversity, it seems the primary determinant of diversity is diet.  Diet can influence diversity in two main ways: introducing different bacteria types and sustaining these different bacteria types.  It may come as no surprise, but the typical American diet does not promote diversity (U-S-A! U-S-A!).  Luckily changing this is relatively easy. 

To introduce different bacteria types, the idea is that you just have to eat probiotics.  These probiotics have living bacteria that can take up residence in your gut.  There are a number of ways to ingest probiotics.  Fermented foods like yogurt, kimchi, tempeh, and kombucha all contain bacteria.  Probiotics also come in supplement form like pills and powders.  

Here’s where things get a little tricky.  Probiotics are great for increasing gut bacteria diversity in unhealthy individuals (or following an antibiotic treatment).  However, in already healthy individuals, the science isn’t clear that probiotics increase gut bacteria diversity (5).  That being said, probiotics have been shown to improve athletic performance.  This may be related to gut bacteria improvements but the actual mechanism is not well understood (3). 

Now it’s one thing to introduce bacteria, but the bacteria aren’t going to survive unless they get fed.  To sustain your diversity, you’ve got to feed the bacteria.  Bacteria can feed off a variety of nutrients but the optimal source is dietary fiber (6). You aren’t able to digest dietary fiber so it travels through the digestive tract down to the large intestine where the bacteria are then able to use the fiber as fuel. 

The primary source of dietary fiber is fruits, vegetables, and whole grains. There are also fiber pills you can take (often called “prebiotics”).  However, to best sustain diversity in the gut, you want to consume a diverse diet of fruits, vegetables, and whole grains.  An added benefit of this diverse food intake (particularly dietary fiber), is that it also is a way to increase gut bacteria diversity (6).  The more diverse the diet, the more diverse the gut bacteria (4).

There are other aspects of diet that can potentially influence the gut bacteria.  For example, it has been suggested that animal products treated with antibiotics could influence the gut bacteria in humans (4,7).  The USDA sets rules about antibiotics based on levels that appear in the blood of humans but these antibiotics may still influence bacteria in the gut and alter diversity.  The same has been suggested of pesticides (4).  The best thing to do then, is to eat antibiotic free meats and organic fruits/vegetables. 

Now hopefully this overview hasn’t left you pooped (I held off on the puns for as long as I could…).  But just like in fashion, it’s exciting to see where this latest science craze leads us.  A lot of the research suggests gut bacteria may be the next frontier for improving overall health and possibly athletic performance.  In the meantime, keep eating those fruits and veggies.  Thanks for reading!