10% Human

1. You are a superorganism, a collective of human and microbial cells.

For every one of the cells that make up the vessel that you call your body, there are nine impostor cells hitching a ride.

More microbe than human. Your body is not just made of human cells; it's a complex ecosystem hosting trillions of microbes, primarily bacteria, fungi, viruses, and archaea. These microbial cells outnumber your human cells ten to one. Their collective genes, the microbiome, contain millions more genes than your own genome.

A shared existence. This vast microbial community lives in and on you, forming a superorganism. They are not mere passengers but active participants in running your body. This co-existence is deeply rooted in evolutionary history, with animals and microbes evolving together in a mutually beneficial partnership.

Beyond human genes. While the human genome provides the blueprint for your body, the microbiome adds immense functional complexity. These microbial genes perform services that are faster to evolve and more easily provided by simple organisms, collaborating with your 21,000 human genes to keep you alive and healthy.

2. Your microbes are a vital, often forgotten, organ essential for health.

We have come to depend on our microbes, and without them, we would be a mere fraction of our true selves.

An integral organ. The human body's microbial community, particularly in the gut, functions like a vital organ. It's involved in processes far beyond simple digestion, influencing metabolism, immune system development, and even brain function.

Essential services. Microbes provide services humans cannot perform alone.

• Synthesizing essential vitamins (like B12).
• Breaking down tough plant fibers indigestible by human enzymes.
• Training and regulating the immune system.
• Influencing energy extraction and storage from food.

Co-evolved partnership. This relationship is not just tolerance but active encouragement. Structures like the appendix, once thought useless, are now seen as safe-houses for beneficial gut microbes, highlighting the body's investment in maintaining this microbial community.

3. Modern life's war on microbes fuels a rise in chronic illnesses.

Our twenty-first-century lives are a kind of sterile ceasefire, with infections held at bay through vaccinations, antibiotics, water sanitation and hygienic medical practice.

The new normal. While infectious diseases have dramatically declined in developed countries over the past century, a new set of chronic conditions has risen to prominence. These include allergies, autoimmune diseases, obesity, gut disorders, and mental health conditions.

A shift in disease. These "twenty-first-century illnesses" were rare among our ancestors but are now common, affecting large portions of the population, often starting in childhood or young adulthood.

• Allergies affect nearly half of people in developed countries.
• Autoimmune diseases affect nearly 10%.
• Over half of adults are overweight or obese.
• Autism prevalence has more than doubled in a decade.

Beyond genetics. This rapid rise cannot be explained by changes in human genetics alone, as evolution doesn't happen that fast. Instead, it points to significant changes in our environment and lifestyle, particularly those related to our interaction with microbes.

4. Many 21st-century diseases stem from gut dysfunction and inflammation.

These two themes, the gut and the immune system, might also seem unrelated, but a closer look at the anatomy of the gut provides a further clue.

Gut-immune connection. The gut is home to the largest concentration of immune cells in the body (around 60%). This strategic positioning allows the immune system to monitor the vast microbial community and substances passing through the digestive tract.

Dysbiosis and inflammation. Disruptions to the normal balance of gut microbes (dysbiosis) can lead to increased permeability of the gut lining ("leaky gut"). This allows microbial products and undigested food particles to enter the bloodstream, triggering chronic low-level inflammation throughout the body.

Underlying cause. This inflammation is increasingly recognized as a common factor underlying many 21st-century illnesses.

• Obesity: LPS from gut bacteria triggers inflammation in fat tissue.
• Autoimmunity: Immune system attacks self cells amidst chronic inflammation.
• Allergies: Immune system overreacts to harmless substances.
• Mental Health: Brain inflammation linked to gut dysbiosis.

5. Antibiotics disrupt your microbiome with lasting consequences.

However, our triumph over our greatest natural adversary – bacteria – has taken place in ignorance of the collateral damage that antibiotics have been causing along the way.

Collateral damage. Antibiotics, while life-saving against pathogenic bacteria, are broad-spectrum and kill beneficial microbes too. This disruption to the microbiome can have long-term effects, potentially lasting months or even years after treatment ends.

Beyond resistance. The overuse of antibiotics contributes not only to antibiotic resistance but also to dysbiosis, which is linked to chronic illnesses.

• Increased risk of C. diff infections.
• Association with higher rates of allergies and asthma in children.
• Potential link to weight gain and obesity (used as growth promoters in livestock).
• Possible connections to autoimmune diseases and autism.

Early life impact. Antibiotic exposure early in life, when the microbiome is still developing, may have particularly profound and lasting effects on metabolism and immune programming. This highlights the need for judicious use of these powerful drugs.

6. Diet, particularly fiber, is crucial for nurturing beneficial microbes.

You are what you eat. What’s more, you are what they eat.

Feeding your microbes. The food you eat doesn't just nourish your human cells; it feeds your microbial community. Different foods, particularly complex carbohydrates like fiber, selectively promote the growth of different microbial species.

Fiber's vital role. A diet high in fiber, common in pre-industrial societies but low in modern Western diets, supports a diverse and beneficial gut microbiome.

• Fiber-loving bacteria produce short-chain fatty acids (SCFAs) like butyrate.
• SCFAs nourish gut lining cells, reducing permeability ("leaky gut").
• SCFAs influence immune cells, promoting tolerance and reducing inflammation.
• SCFAs can impact appetite regulation and energy storage.

Beyond calories. The nutritional value of food is not just about calories absorbed by human enzymes but also about what microbes extract and the beneficial compounds they produce. A diet low in fiber starves beneficial microbes, potentially contributing to dysbiosis and inflammation.

7. Early life exposures shape your foundational microbial community.

In the first few hours of a baby’s life, it goes from being mostly human to mostly microbial, in terms of cell numbers at least.

Microbial inheritance. Babies acquire their first crucial microbes during birth and through early feeding. This initial microbial seeding is vital for immune system development and establishing a healthy gut ecosystem.

Birth mode matters. Vaginal birth exposes babies to the mother's vaginal and fecal microbes, providing a diverse inoculum rich in beneficial species like Lactobacillus and Prevotella. Caesarean section babies are primarily colonized by skin and environmental microbes, resulting in a less diverse initial microbiome.

Breast milk's role. Breast milk contains unique oligosaccharides that human enzymes cannot digest but selectively feed beneficial bacteria like Bifidobacterium. It also contains live bacteria and immune factors that help shape the infant microbiome and train the immune system.

• Bottle-feeding with formula results in a less diverse microbiome dominated by different species.
• Bottle-fed babies have higher risks of infections, allergies, autoimmune diseases, and obesity.

8. Restoring microbial balance offers a path to better health.

The beauty of the microbiota is that, unlike our genes, we have some control over it.

Reversing dysbiosis. For conditions linked to microbiome imbalance, restoring a healthy microbial community holds therapeutic potential.

• Faecal Microbiota Transplantation (FMT) involves transferring stool from a healthy donor to a patient. Highly effective for recurrent C. diff infections (over 90% cure rate). Showing promise for IBS and metabolic syndrome.
• Probiotics (live beneficial bacteria) and Prebiotics (fiber that feeds beneficial bacteria) can help modulate the microbiome, offering benefits for various conditions, though often less dramatic than FMT for severe dysbiosis.

Conscious choices. While medical interventions are developing, individuals can actively cultivate a healthier microbiome through lifestyle choices.

• Eat More Plants: Increase fiber intake from diverse plant sources.
• Use Antibiotics Judiciously: Avoid unnecessary prescriptions and understand the risks.
• Support Natural Birth & Breastfeeding: Advocate for and choose these options when medically appropriate.

Empowerment. Understanding our microbial selves empowers us to make informed decisions about our health and the health of future generations, moving towards a state of being truly 100% human.

Last updated: May 14, 2025