We (humans) are a host to many many microbes - bacteria, fungi, protozoa and viruses. In fact, there are trillions of them. That is more than we have cells in the human body. It was often assumed that the the number of microbes outnumbered the number of cells in the body by about 10-fold, but more recently this myth was busted. The majority of these microbes live in our gut, particularly in the large intestine. In total these microbes may weigh as much as 1.5-2.5 kilograms (3-5 pounds).
The term microbiome although technically meant to represent the genetic material of all the microbes, is often used to describe our collection of microbiota. The microbiome could be regarded as the human equivalent of an environmental ecosystem. Because the existence of the microbiome was not generally recognized until the late 1990s, our understanding is still in its infancy.
The bacteria in and on our bodies are likely involved in a number of important functions. For example:
1. The microbiome helps digest our food,
2. Regulates our immune system
3. Protects against other bacteria that cause disease, and
4. Produces vitamins including several B vitamins (vitamin B12, thiamine and riboflavin) and Vitamin K.
Role of the microbiome
The microbiome is essential for human development, immunity and nutrition. Thus the bacteria living in and on us are not invaders but beneficial colonizers. Autoimmune diseases such as diabetes, rheumatoid arthritis, muscular dystrophy, multiple sclerosis, and fibromyalgia have been associated with dysfunction in the microbiome. Disease-causing microbes accumulate over time, changing gene activity and metabolic processes and resulting in an abnormal immune response against substances and tissues normally present in the body. It has been suggested that autoimmune diseases are passed in families not by DNA inheritance but by inheriting the family’s microbiome.
Studies also suggest that the gut microbiome is different between obese and lean twins. Obese twins have a lower diversity of bacteria, and higher levels of enzymes, meaning the obese twins are more efficient at digesting food and harvesting calories. Obesity has also been associated with a poor combination of microbes in the gut. Some have suggested that the variety of gut microorganisms is decreasing as a result of changes in diet and this is the cause of disease.
A word of caution
There has been a huge interest recently in the microbiome and its role in health, disease and even performance. There has been a lot of attention in the media and a huge hype has been created around it. It is important to realize that the microbiome plays a role, but its role is also often exaggerated. We have a lot to learn still and it is too early to draw very firm conclusions. An article in the Times was titled “We are our bacteria” seemed to suggest a dominant role of bacteria in our bodies.
There are many claims and not a lot of conclusive answers yet. All we know is that many claims are based on correlations and these do not necessarily need to be causal relationships. Drawing simplistic conclusions from incredibly complex systems such as the microbiome, are likely to be flawed. So next time your read about the microbiome please keep this in mind.
An important way to explore the role of the microbiome for athletes is by altering the microbiome and studying the effects. Currently, one of the easiest and main dietary strategies to change gut microbiota is the use of probiotics. In a next blog Professor Mike Gleeson will discuss the effects of probiotic supplementation in athletes.