So, What Is the Microbiome?
The term microbiota refers to the collection of microbes living in and on the human body. The microbiome, on the other hand, is the complete set of genes within these microbes. These microbial genes play a crucial role in how our bodies function and even outnumber human genes by a ratio of 100:1. Each person has a unique microbiota and microbiome, influenced by various factors such as exposure, geography, health status, stress, diet, age, gender, and everything we come into contact with. These microbial colonies are constantly changing.
Public Health, Germ Theory, & the Microbiome
Scientists have been aware of microorganisms for centuries. In 1673, Antony van Leeuwenhoek wrote to the Royal Society of London about his discovery of tiny “animalcules” using his microscopes. Although he found microbes almost everywhere, his discovery was largely ignored until the 1870s when their role in disease causation and spread was recognized. Before this, doctors believed that bad air caused diseases. Robert Koch’s work proved that tiny microorganisms were responsible, solidifying the germ theory—the idea that specific microbes cause specific diseases.
Germ theory provided a scientific basis for cleanliness, which then became a moral and social imperative. People began bathing daily, and soap transitioned from a luxury to a household necessity. Medical professionals started washing their hands and sanitizing their instruments. New public health laws and initiatives emerged, limiting the spread of diseases and saving lives.
For a long time, scientists focused mainly on how pathogenic microbes negatively affect humans. However, there has been a shift towards understanding that some microorganisms are beneficial to human health. The Human Microbiome Project (HMP), launched in 2008, aims to better understand the relationship between health, disease, and the microbiome.
The Makeup of the Microbiome
The microbiota consists of an enormous number of microorganisms, with bacteria making up the majority—about 30-50 trillion cells. In comparison, the human body contains about 37 trillion human cells. While it might seem like we are mostly microbial cells, by weight, we are predominantly human since microbial cells are much smaller than human cells. Bacterial cells range from 0.2-10 microns across, whereas human cells range from 10-100 microns. For context, the average dust mite, which is microscopic, is 200-300 microns wide.
The often-quoted 10:1 ratio of microbes to human cells was just an estimate and is now considered an academic urban legend. It’s believed that humans carry about three pounds of bacteria in their intestines. Each person’s microbiome is unique, much like a fingerprint, and consists of hundreds of different types of bacteria. The number of bacterial cells varies throughout the day and is always turning over.
Although bacteria account for most of the microbiota’s mass, viruses are the most abundant inhabitants. We often think of viruses as harmful, but that’s not always the case. The viruses in the gut are primarily bacteriophages, which infect gut bacteria cells but don’t necessarily harm them. Instead, they have a symbiotic relationship. Viruses can quickly transfer beneficial genes, helping new bacteria introduced through diet or probiotics to thrive.
The Role of the Human Microbiota
The microbiome is so integral to the body’s operations that it essentially acts as an organ. It impacts aging, digestion, the immune system, mood, and cognitive function. Some gut bacteria produce enzymes that aid in digesting polysaccharides—healthy, complex sugars found in plant foods. These bacteria also provide B vitamins, vitamin K, and short-chain fatty acids, and influence metabolic rate.
A strong microbiome is the foundation of your immune system. At birth, your gut is a clean slate, ready to learn. Exposure to microbes educates the immune system on how to respond to different organisms. The immune system mediates the relationship between the body and its microbial inhabitants, dealing with harmful organisms and coexisting with beneficial ones to promote overall health.
Research has also highlighted the microbiome’s significant role in mental health. The gut-brain axis (GBA) describes the complex relationship between the gut and brain. The microbiota interacts with the central nervous system to regulate brain chemistry and mediate stress response, anxiety, and memory.
How Is the Human Microbiota Formed?
It’s generally agreed that the human body is first exposed to microbes during birth. The mother’s microbiota changes during pregnancy and significantly influences the newborn. Babies born vaginally are primarily colonized by the Lactobacillus genus of bacteria, while those delivered by Caesarean section are exposed to skin microbes such as Staphylococcus, Corynebacterium, and Propionibacterium. The birth environment, whether at home or in a hospital, also affects the baby’s microbiota composition.
As babies grow, their microbiome changes. In the first few months of life, the body is colonized by relatively few species of microbes—about 100. By age three, a child’s microbiota contains closer to 1,000 species and begins to resemble that of an adult. Puberty and menopause are other life events that can significantly alter the microbiota’s composition.
The Bacteria in Your Gut Microbiome
The microbiome composition varies throughout the intestines, with most bacteria concentrated in the large intestine. The average adult gut contains bacteria such as Bifidobacterium, Lactobacillus, Bacteroides, Clostridium, Escherichia, Streptococcus, and Ruminococcus. Diet influences the microbial composition of the microbiota, which in turn affects the nutritional value of food. Although specific bacteria vary, they share many of the same genes.
Humans lack the enzymes needed to break down complex nutrients, but gut bacteria possess this ability, which is essential for proper digestion. Bacteria enable us to consume a diverse diet and obtain a broad range of micronutrients and phytonutrients.
Supporting the Microbiome
Your microbiome is constantly changing and plays a vital role in processes like digestion and immune system function. To strengthen your microbiome, eat a diverse diet rich in complex carbohydrates and fiber. Probiotic supplements can also help. The best probiotic supplements contain a variety of probiotic strains and prebiotics, which are foods that help probiotics flourish.
I personally recommend Global Healing’s Ultimate Probiotic. It contains 25 different probiotic strains that support digestive health, mood, and promote a balanced microbiota, along with prebiotics.