The human body is a walking ecosystem. We all learned this from high school biology; all throughout our bodies, day in and day out, hundreds and even thousands of organisms are working with (and sometimes against) our body.

This is what we like to call a microbiota. Our microbiota is the collection and community of microorganisms living inside our bodies- they are a part of our skin, lungs, saliva, blood, and intestines. Long story short: they are everywhere and we need them to survive.

As evolutionary biologist Rob Dunn PhD, author of Wildlife of Our Bodies, said:

“Everyplace you have ever set your hand or any other part of your body is covered in microbes. This is true of your gut, but also everything else. Microbes live in clouds. They live in ice. They live deep in the Earth. They also live in your colon, on your skin, and so on.”

Millions of years ago, in a much dirtier time, the human body had many more microbes, with more diversity, living symbiotically in our bodies. With many of these relationships, mankind co-evolved with the microbes to become almost dependent upon them to fully function properly. As the human race got cleaner and cleaner, we began to lose those symbiotic relationships, and as a result, lose those important relationships we depended on for generations.

So because we are cleaner than cavemen our bodies are in harm’s way?

The precise connection between microbes and a hosts’ health is still unclear; however, a study done by six major scientists from Stanford School of Medicine, Harvard and Princeton University has established a link between diet and how diverse your microbiota is.

In western culture, people typically have a high fat, low fiber, and simple carbohydrate diet, while hunter-gatherer and agrarians tend to have a diet high in dietary fiber. Dietary fibers are carbohydrates that our body cannot break down and they pass through the stomach and upper intestines without being absorbed allowing microbes to use dietary fiber as an energy source. In light of this, scientists have begun referring to the dietary fiber that microbes can digest as MACs, or Microbiota-accessible carbohydrates. MACs can be seen in high fiber foods such as grains and vegetables, and therefore are more commonly present in hunter-gatherer populations whose main food source are unprocessed high fiber foods.  

Why does this matter?

MACs function as the primary source of energy for the distal gut microbiota, so if there aren’t enough MACs in our diet, the gut microbiota start to starve out and die.

In the study, the researchers wanted to see if a diet that was low in MACs caused permanent loss of certain gut microbiota across multiple generations. These researchers took mice infected with a large range of microbiota and fed them high-MAC (high fiber) diets and then separated them into two groups. One group was the control group, receiving a high-MAC/fiber diet constantly, while the other group was put on a low-MAC/fiber diet. Each step of the way they measured the mice’s microbiota diversity and what they found supported their hypothesis on the MACs effect on microbiota.

The mice who were placed on the low-MAC/fiber diet had a 60% reduction in their microbiota diversity while the high-MAC mice maintained their diverse microbiota.

The researchers then decided to see if this loss of microbial diversity could be restored if low-MAC mice were put back on a high-MAC diet. The low-MAC mice were then given high fiber foods for an extended amount of time and their microbiota was then re-measured. They found that only 33% of the lost diversity was regained.

Then the researchers took the experiment one step further, they wanted to see if this vast loss of microbiota diversity would persist into future generations.

The result?

The parent mice that were given a low-MAC diet and showed microbiota diversity loss all produced offspring and generations of mice with reduced microbiota diversity as well. This loss in the offspring’s microbiota were even observed when the offspring were given high-MAC diets, showing that the loss was permanent and passed down directly from the parents.

So what is the take away from all this?

Over many generations, mankind has turned from a culture of fiber rich, home grown foods, to highly industrialized processed foods low in natural dietary fiber. This change in diet overtime, alongside with the constant sterilization and increase in cleanliness of humans, has led to a reduced diversity of microbes in our gut.

So, while its easier to grab pre-made food at the grocery store rather than harvest and cook fresh vegetables, our over processed lives may be hurting us more than we know. Microbes have been an important part of our existence since day one- these microbes have co-evolved with us, many even becoming a part of our core functions and DNA. Now, the advantages we once saw in the ease of processed foods, may be outweighed by the disadvantages of what it means to lose microbiota in our bodies.

We may not be able to say what each and every specific microbe’s functionality in our body is yet, but we do know that the microbiota in our gut plays an important role in our digestion, and that our new diets are causing a depletion of these symbiotic relationships.

So, while we don’t necessarily want worms swimming around in our gut all the time, mankind may need to reconsider the role of microbes in our health and begin to think about their true importance in order to be the healthiest we can be.

Study:

Sonnenburg ED, Smits SA, Tikhonov M, Higginbottom SK, Wingreen NS, Sonnenburg JL. Diet-induced extinctions in the gut microbiota compound over generations. Nature. 2016;529: 212–215. doi:10.1038/nature16504

Additional Resources:

Jandhyala SM, Talukdar R, Subramanyam C, Vuyyuru H, Sasikala M, Reddy DN. Role of the normal gut microbiota. World J Gastroenterol WJG. 2015;21: 8787–8803. doi:10.3748/wjg.v21.i29.8787

Derrien M, Veiga P. Rethinking Diet to Aid Human–Microbe Symbiosis. Trends Microbiol. 2017;25: 100–112. doi:10.1016/j.tim.2016.09.011

So, You want to Know Which Species Live in Your Gut By Rob Dunn Evolutionary Biologist, North Carolina State University - PDF [Internet]. [cited 9 Feb 2017]. Available: http://docplayer.net/27755523-So-you-want-to-know-which-species-live-in-your-gut-by-rob-dunn-evolutionary-biologist-north-carolina-state-university.html

Olivia Langa (’18) is a junior at Bucknell University working towards her B.A. in both Biology and Theatre while on a Pre-Med track.

Interested in becoming a pediatrician, Olivia is a research assistant at Geisigner Hospital’s ADMI center working on children with neurodevelopment disorders.

Outside of the lab, Olivia is the Vice President of Chapter Relations in the Eta Chapter of Alpha Chi Omega, as well as a member of the Bucknell Admissions Ambassador team. Post-graduation, she plans to take a gap year before medical school to continue in research in clinical labs working with children.