Healthy Focus: The Microbiome
What is a Microbiome?
The collection of microbes that live in and on the human body is known as the microbiota.1 The microbiome refers to the complete set of genes within these microbes. Microbial genes significantly influence how the body operates and even outnumber human genes by a ratio of 100:1.2 Each of us has a unique microbiota and a unique microbiome. The microbes that live in your body are determined by what you're exposed to and these colonies are constantly in flux. Geography, health status, stress, diet, age, gender, and everything you touch all affect the composition of your microbiota.3
The Microbiome and Public Health:
Scientists have known about microorganisms for hundreds of years. In 1673, Antony van Leeuwenhoek wrote to the Royal Society of London about his discovery of tiny “animalcules” with the use of his “microscopes.” Leeuwenhoek found microbes almost everywhere he looked,4 but the discovery was largely ignored until the 1870s when their role in the cause and spread of disease was observed. Previously, doctors believed that bad air caused disease. Robert Koch proved that tiny microorganisms were responsible. His discovery solidified the validity of germ theory — the idea that certain microbes cause specific diseases.5
Germ theory created a scientific rationale for cleanliness that became the precursor to it becoming a moral and social imperative. People began bathing daily. Soap, once considered a luxury, became a basic household necessity. Doctors and surgeons started washing their hands and sanitizing their instruments.6 New laws led to public health initiatives that limited the spread of disease and saved lives.6
Until recently, scientists focused almost solely on how pathogenic microbes negatively affect humans. There has since been a realization that some microorganisms are actually beneficial to human health.7 More attention is now given to the microbiome and its role in health and immunity.8 Launched in 2008, The Human Microbiome Project (HMP) was created to better understand the relationship between health, disease, and the microbiome.9
How is the Microbiome designed?
The microbiota is comprised of a dizzying number of microorganisms. Bacteria make up the bulk — about 30-50 trillion cells.10 The human body itself contains about 37 trillion human cells.11 It may be disconcerting to think of yourself as mostly microbial cells, but, by weight, you’re definitely mostly human as microbial cells are significantly smaller than human cells. Bacterial cells range from 0.2-10 microns (micrometers) across; human cells range from 10-100 microns.12 For reference, the average dust mite, which is microscopic, is 200-300 microns wide.
It's believed that humans carry about three pounds of bacteria in their intestines.13 Everyone's individual microbiome is as unique as their fingerprint and comprised of hundreds of different types of bacteria.14 The specific number of bacteria cells varies throughout the day and is always turning over.15
Bacteria and the Microbiome:
Although bacteria account for most of the mass of the microbiota, viruses are actually the most abundant inhabitants.8,16 We tend to think of viruses as harmful, but that’s not always the case. The viruses found in the gut are primarily bacteriophages, meaning that they infect gut bacteria cells but they don't necessarily harm them. Rather, they have a symbiotic relationship. Viruses can quickly transfer genes — beneficial genes. So, if new bacteria are introduced to your gut, either through diet or probiotics, the viral cells can help the bacteria thrive by transferring the genetic code.17
What is the Microbiome’s Role?
The role of the microbiome is so central to the body’s operations that it essentially acts as an organ.18 The microbiome impacts aging, digestion, the immune system, mood, and cognitive function.
Some of the bacteria in the gut produce enzymes that support digestion, especially the digestion of polysaccharides — healthy and complex sugars found in plant foods.19 These bacteria also provide B vitamins, vitamin K, and short chain fatty acids. The microbiota also influences metebolic rate.19
A strong microbiome is the foundation of your immune system. When you were born, your gut was a clean slate, ready to learn.20 Exposure to microbes provides the education that trains the immune system how to respond to different organisms. In this way, the immune system mediates the relationship between the body and the microbes it hosts.20 Harmful organisms are dealt with, helpful organisms exist in harmony and contribute to good health overall.21
Research has also revealed the important role the microbiome has on mental health. There is a complex relationship between the gut and the brain, called the gut-brain axis (GBA). The microbiota interacts with the central nervous system to regulate brain chemistry and mediate stress response, anxiety, and memory.22
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