Our Second Self: Microbiome 101

Our Second Self: Microbiome 101 - Moodbeli


It's easy to think of our microbiome as something new or separate from us. But we've been evolving alongside microbes from the very beginning. Evolutionary biologists have found families of bacteria in the human gut that trace their bacterial ancestors back over 15 million years.

We have 30 trillion human cells in our body, but we have 39 trillion microbial cells living symbiotically on and inside of us. By cell count, that means we're outnumbered by other living organisms that we inherited from our ancestors and picked up along the way from our environment. The cells that make up our second self aren't just along for a free ride, they're integral actors in almost every single function we perform. Our microbiome influences our digestion, immunity, skin, inflammation, sleep, heart, metabolism and ultimately how we think, feel, and act.


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Inflammation & Immunity

A large part of our immune system is located in the gut. Promoting a healthy immune response and inhibiting inflammation relies on the right blend of gut microbes. 


As many as 1000 different species of bacteria live on our skin. Interactions between our skin cells and our microbiome help repair and strengthen our skin barrier and protect us against infection.


Evidence is emerging that our gut microbiome can influence our circadian rhythm. Loss of microbe diversity can eliminate serotonin in the gut, which is required for a healthy sleep-wake cycle. 


There's a bi-directional relationship between our mood and our microbiome. Changes in our microbiota can alter the symptoms of mood disorders, while mood disorders can change the makeup of our intestinal microbiota. 


Gut bacteria can directly effect the plaques that cause heart disease, and influence whether we develop risk factors for heart disease like obesity and diabetes.


Our microbiome produces metabolites and plays a key role in our metabolism. Removing a single gene from a certain strain of gut bacteria in mice, changed their metabolism and reduced weight gain.


The idea that our gut influences how we feel is not new in human history. They're called "gut feelings" for a reason. Ancient Greeks believed certain types of bile in the digestive tract could impact mental health. British doctors in the 1800s wrote of how digestive disorders could lead to what they called "diseased emotions". And the link between our gut and how we feel has been recognized in Traditional Chinese Medicine for thousands of years—the production of vital Qi energy depends on good digestive health and deficiencies in Qi can result in both physical and mental symptoms.

Every one of us is a constant collaboration between our own physical body and trillions of other beings. We're truly never alone nor are we distinct from nature. We'll probably never be able to isolate which bacteria causes which emotion at any given moment, but living a pro-probiotic lifestyle is shown to have a myriad of good outcomes.

Save this post for when you're feeling lonely, or need a reminder to celebrate both of your selves from the inside out.

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  1. S. Fitz-Gibbon et al. Journal of Investigative Dermatology
  2. Q. Mu et al. Frontiers in Immunology
  3. Y. Ogawa et al. Scientific Reports
  4. L. Liu et al Frontiers in Psychiatry
  5. L. Yao et al eLife
  6. J. Kelly et al Frontiers in Cellular Neuroscience
  7. Q. Ma et al Journal of Neuroinflammation
  8. I. Miller Microbial Ecology in Health and Disease


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