The Human Microbiome Project (HMP) (2008-2013) is by far the most extensive study of the microbes that live in and on the human body. Hundreds of scientists worked on the five year long project, and DNA sequencing was used to map the critters living in the gastrointestinal tract, mouth, vagina, and other body sites.
While we’ve know for some time that the human body is not sterile and that bacteria coat our skin and help us digest food in the large intestine, recent findings from the HMP and other research projects around the world show that the microbiome (microbes and their genes) is far more important than we’ve realised.
As it turns out, trillions of microorganisms from thousands of different species live “in” and on our bodies. In total, more than 75% of the cells in the human body are microbial, and the microbial genetic repertoire is more than 100-times greater than that of the human host (1,2). This means that if you look at the human body from a genetic perspective, we are actually only 1% human.
Each human harbours an unique combination of microorganisms, and although it’s to early to tell exactly how a healthy microbiome looks like, it’s already clear that some germs have a positive effect on human health while others are potentially pathogenic (3).
The human microbiome is perhaps the hottest research subject in the scientific community at the moment, and current findings suggest that we have to rethink our entire perspective on health and nutrition. Studies show that microbes are directly or indirectly involved in the pathogenesis of most of the chronic health problems we see today, ranging from gastrointestinal disorders such as gallstones to skin problems like acne (4,5). Bacteria in the gut also seem to play an essential role in weight regulation, and obese individuals harbor different types of microbes compared to lean individuals (6). The human microbiome even seems to affect our mood, behaviour, and thoughts (7).
Rather than looking at the human being as a single organism, it’s clear that we should think about Homo sapiens as an ecosystem with trillions of microorganisms living symbiotically with the human host. The human host provides these microbial communities with shelter and food, and the microbiome provides us with metabolic functions that stretch far beyond the scope of our own physiological capabilities.
Animated video explaining the human microbiome
This video from npr.org is excellent for those people that want a simple description of what the human microbiome really is.