What Is the Microbiome?

The existence of micro-organisms has been known to science for more than 400 years, but it’s only in the last century or so that the complex relationship between humans and bacteria has been closely examined. And it’s only in the last couple of decades that we’ve started to understand just how important the bacterial populations that live on and inside human bodies really are—to our digestive health, the strength of our immune systems, and even to the health of newborn children.

 

Your Body is Home to Trillions of Bacteria

Estimating the number of cells in the human body is difficult, but at a minimum, there are 10 trillion—a staggering, almost unimaginable number. That number is itself difficult enough to comprehend, but imagine this: in the human body, bacterial cells outnumber human ones by ten to one. There are 100 trillion bacteria living in and on the average human body, and there’s an increasing body of evidence to support the idea that having the right balance of different bacterial species living in our bodies is important for good health.

The population of cells that live on the body are called the microbiome, and it’s made up of thousands of different species. A rough estimate is that more than 3,000 different species live in our guts, three to four hundred on the skin, and more than 700 in the vagina. There are up to 5,000 species that can live in the human mouth, although only 100 or so are typically found in the average person’s mouth.

 

How You Benefit from Your Microbiome

The scientific study of the microbiome and its effects are still in the early stages, but even so, some interesting and significant facts have already been uncovered. For example, lab studies have shown that mice reared in sterile bacteria-free conditions don’t have a microbiome. These bacteria-free mice have dysfunctional immune systems, with abnormally high levels of inflammation-causing cells, and a greatly increased risk of developing asthma and inflammatory bowel disease. As well as this bacteria in the gut have been shown to have some surprising effects. They can influence the way your body metabolizes sugar, and, amazingly, may even modify brain chemistry.

 

The Microbiome Before and After Birth
Numerous studies have shown that a person’s microbiome changes when they become pregnant. In the vagina, for example, a bacterial species called Lactobacillus johnsonii grows in large numbers, but in the absence of pregnancy this species is only present in the gut. It’s possible that this bacteria starts growing in the vagina due to “environmental” changes, and that during vaginal birth, a baby is exposed to the bacteria. This exposure effectively inoculates the baby with the bacteria, and helps the newborn digest breast milk.

When a baby is born via cesarean, however, they don’t receive the benefits gained from exposure to the vaginal microbiome. While it’s been suggested that this might have negative consequences for the child’s long-term health, the true impact of cesarean delivery on the microbiome is not yet established.

 

Changing Your Microbiome can Improve Your Health

The thousands of bacterial species that live in the gut have a wide variety of functions: they synthesize vitamins like B12, which humans are unable to make on their own, and they contribute to the synthesis of amino acids too. They produce molecules that effect the body’s insulin response and sugar metabolism, and help the gut digest foods like fibers and starches. It should come as no surprise, therefore, that changes in the gut microbiome can affect digestion and health. These changes can happen very quickly—within about three or four days of a change in diet—and can significantly affect health. For example, there is evidence that a diet high in animal products causes an increase in the population of a bacterial species that contributes to colitis symptoms.

It’s not just food that can cause the composition of your digestive system’s microbiome to change—alcohol and drugs, including both prescription and illicit drugs, can too. For example, antibiotics are known to have a dramatic effect on populations of bacteria in both the gut and the vagina. Probiotic foods and supplements also change the microbiome, by supplying the gut with specific bacterial species.

A small but growing number of medical treatments focus on altering a patient’s microbiome. One is the treatment of antibiotic-resistant Clostridium difficile bacteria, which can infect the gut after a course of antibiotics. The infection is extremely difficult to treat, but fecal transplant, in which a patient’s gut is inoculated with bacteria from a healthy person’s gut, is extremely effective.

 

~~ Researched and written by Anne Hoy

 

References

Carl Zimmer. 2014. “Our Microbiome may be Looking Out for Itself.” In The New York Times. Accessed October 11, 2014.

Drug Treatment. “Hydrocodone Treatment.” Accessed October 11, 2014.

Garden of Life. “Raw Probiotics.” Accessed October 11, 2014.

National Institutes of Health. “Human Microbiome Project.” Accessed October 11, 2014.

Rachel Feltman. 2013. “The Gut’s Microbiome Changes Rapidly with Diet.” In Scientific American. Accessed October 11, 2014.

Second Genome, the Microbiome Company. “The Microbiome and Human Health.” Accessed October 11, 2014.

University of Utah Learning Center. “The Human Microbiome.” Accessed October 11, 2014.