Monday, April 21, 2014

The bacteria in your gut: Your "flexible" genes

Your microbiome, the community of bacteria that live within and on you, has become a hot area of research recently.  This bacteria lives on your skin, in your mouth, all throughout your digestive tract, and basically in any nook or cranny you have.  The bacteria that reside in the digestive tract perform a host of functions for  They help train the immune system, help with mineral absorption, help breakdown things we cannot break down, and make short-chained fatty acids that help keep our digestive tract in tip-top shape.  Many health problems are associated with the composition of bacteria you have in your gut including obesity, Type 2 diabetes, arthritis, IBS/IBD, Crohn's disease, Celiac disease, anxiety/depression, autism, and many others.  This has led researchers to seek out what a healthy microbiome is so that we can manipulate it to promote health.

The many ecosystems that make up your microbiome

The Human Microbiome Project was undertaken to take a glimpse at the microbiome of those in Western society while researchers are also taking a look at modern day hunter gatherers to get a glimpse at how our microbiome may have evolved with us.  One of the more notable findings in hunter gatherers is that they tend to have a much more diverse microbiome than those of us in Western society.  Over the course of the last month, more information has been uncovered looking at both the Western population as well a modern day hunter gatherers.

Researchers from the Human Microbiome Project have analyzed microbiome samples from 300 people and determined that, based on current data, there is no single healthy microbiome.  Based on all of the data to date, healthy people can have a wide range of different microbiomes(1).  Several lifestyle factors such as if you were born by C-section, whether you were breast fed, or past antibiotic usage can impact the microbiome in your GI tract while gender can affect the microbiome in different body sites.  Each person has a signature microbiome that is representative of the environment they grew up in and the lifestyle that they have lived.  In fact, lifestyle has a huge impact on the make up of your microbiome, as seen by a recent study looking at Hadza hunter-gatherers.

In the study, researchers found that even people who live in the same environment, which essentially means they are exposed to the same types of bacteria, have different communities that live alongside, and inside, them.  Hadza men and women differ greatly in the composition of their microbiome, due primarily to the fact that men tend to hunt game and collect honey while the women gather primarily plant foods(2).  While the food is shared, the men tend to snack on more of the foods that they collect while the women tend to snack on more of the foods that they collect.  So despite eating the same foods, even just a small change in the percentage of the foods consumed can significantly change the microbiome.  This makes sense because they eat what you eat but don't absorb.  Plant materials, high in fibrous material that humans cannot digest, provide substrate for bacteria living in the colon.  The colon harbors the largest percentage of bacteria in the digestive tract by far.

Hadza chicks, scarfing fries and discussing the latest Real Housewives of Tanzania episode

One interesting aspect of this study is that the Hadza had a large number of bacterial species that are associated with disease in Western populations and low levels of bacteria that are associated with health. Despite having what one would consider a less than ideal microbiome based on what our research shows, the Hadza don't experience IBS/IBD like we do.  This reinforces the notion that there is not a single healthy microbiome, and points to the total collection of bacterial species that make up your microbiome as being important, not the presence of specific species.

A third study followed a group of people called Hutterites for a year.  Hutterites more closely resemble the Amish in that they are exposed to technology such as medical care, exposure to vehicle exhaust, and electricity.  The Hutterite share a communal lifestyle so they have a very similar microbiome between members.  While this similarity between the microbiome of members of the group remains stable throughout the year, the microbiome of the entire tribe changes with the seasons as the availability of food changes(3).  As the seasons change, so does the microbiome of the tribe as the types of foods they consume changes with their availability.

This study, coupled with this other study(4) that showed that extreme shifts in diet can begin drastically changing the microbiome within hours, paints the microbiome as a shiftable genome that helps the host adapt to the changing environment.  In fact, the number of genes within the microbiome of an individual outnumbers the number of genes that they possess in your cells by an order of 100 to 1, maybe even more.  Western medicine has placed such a large emphasis on how strongly genetic factors play in the many diseases we see, yet until recently has ignored the fact that most of the genes that will have an impact on the many biological functions that go on within the human body are directly influenced by diet and lifestyle. 

While research in the microbiome is in it's infancy, it's great that we are directing so much attention towards it.  Studying the microbiome will likely be the next big step in understanding human health and function.  It is also likely necessary to undo some of the damage we may have done with some of our current medical(Antibiotics) and social(extreme hygiene) practices.  This is not to say that these practices aren't necessary or are bad, merely that understanding them and the way they impact our microbiome more thoroughly will only improve their effectiveness.