Humans: walking eco-systems

Just 20 years ago it wouldn’t have occurred to us that humans aren’t entirely human.

Turns out, humans are really just “hosts” living in a symbiotic relationship with trillions of tiny microbes. Without them, we die. Without us, they die. The higher the diversity of gut bacteria, the better the host’s health.

The lining of the upper colon showing the mucosal layer that keeps our gut lining protected from pathogens (bad bacteria). The red section is microbiome, made up of trillions of bacteria which are mostly good for us. The blue is the blood that receives and transports the chemicals that are made by the microbes in the microbiome that keep us healthy (Photo from the Stanford Centre for Clinical Research)

Scientists have long known that there’s tiny single celled critters living in and on us, but it was only recently that we have worked out just how critical they are to our functioning.

No-one had any idea there were so many microbes, and such a variety, or that they were critically important to human health.

It’s only in the last 20 years that scientists have been able to grow the bacteria to see them under a microscope, and that they’ve had computers powerful enough to crunch the information. Our bodies contain around 80 trillion cells but only 30 trillion are human; the rest are bacteria (microbes) – thousands of different species, all playing their part in the eco-system that is your body.

Not only that - genetically we’re 99 per cent microbe! Only 1 per cent of us is really “human”; the microbiome contributes more genes responsible for human survival than humans contribute. The human genome carries some 22,000 genes while it’s estimated that the microbiome has around 9 million unique genes. We carry 360 times more bacterial genes than human genes.

This is important because it means that a predisposition to disease and illness is not as “genetic” as we used to think. In fact for most conditions that affect modern humans – the so-called Non Communicable Diseases –heart disease, stroke, cancer, liver disease and type 2 diabetes, genes only count for between ten and 20 per cent. The rest is up to you and your lifestyle (and your microbes).

We’ve got microbes in every nook and cranny, inside and outside of us. The largest, and potentially, most important collection, is the gut microbiome; the microbes that live in your digestive system. If you pat the right side of your stomach just under your rib cage, you’ll be saying “hello” to your gut microbiome. And that’s a great thing to do because looking after it is a great way to ensure your long term health.

The discovery of the microbiome is so recent that biology and nutrition books from the 80s and 90s don’t list the words “microbiome” or “microbiota” in the index. The books do talk about microbes but more in the sense that they contribute to the fermentation of food in the gut and made our poo smell.

It was thought the colon was largely inanimate and just processed food so it could be excreted. A 1990 university text book, in a chapter on digestion, states: “faeces consist mainly of materials that cannot be digested…” (pp 562)

We now know that’s far from correct. Every meal you eat is digested with the help of the bountiful bacteria thronging your intestines. These bacteria are born and die in very short time frames so dead bacteria comprise a large part of our excreta. Humans have evolved to have difficulty processing fibre – because we didn’t need to – we’ve got our symbiotic microbial friends to do it for us.

We’ve outsourced the entire process of digesting complex carbohydrates to the bugs and they do it by teaming up and fermenting the leaves and stalks and seed husks that come their way. The fermentation process is really the microbes gorging and excreting but microbe excreta is the best thing that can happen to you! Sort of like putting horse manure on the garden to enrich the soil.

A healthy gut means a healthy human. The greater the variety of plant matter eaten, the greater the variety of microbes, the greater the variety of excreta or to use the scientific name “metabolites”. These metabolites pass through the colon wall to keep your insides healthy and fight inflammation.

Our health is dependent of keeping the microbes happy and feeding them what they need to survive and thrive: the fibre found in legumes, peas, beans, vegetables, seeds, nuts, grains, fruits, herbs and spices – any whole foodstuff that has a relationship with the ground!All health starts in the gut and the single greatest predictor of a healthy gut microbiome is the diversity of plants in your diet.

Fibre is only found in plants. There is no fibre in any animal product. Our colon critters need a huge variety of different vegetables and plants, which makes sense, seeing as there’s thousands of different species housed within us.

What does the Microbiome Do?

A better question is what doesn’t the microbiome do? The metabolites that the microbiota produce impact on almost every function of the human body. The immune systems is mostly in your gut; mood is controlled by hormones that are produced and inflammation is controlled through the gut.

Given that inflammation is the root cause of the diseases that kill around 70 per cent of Australians*, there’s very good reason to take good care of those critters because they:

• Maintain Gastrointestinal Motility (pushing stuff through the colon)

• Support gut wall integrity (keeping the wall of the intestine strong so immunity stays strong)

• Compete with pathogens (making sure the bad bacteria can’t build up)

• Produce Short Chain Fatty Acids (Metabolites which are critical “post-biotics” that look after the lining of our gut and are potent anti-inflammatories)

• Synthesise vitamins (food does not contain vitamins, our bodies actually make them from different stuff such as K2, B12, folate and thiamine)

Even though you might have a genetic “predisposition” to a disease or illness the gut bacteria can influence the expression of your genetic code. Every single microbiome in the world is unique. Even identical twins, who share DNA, do not share a microbiome, so we can’t say for certain what a “normal” microbiome looks like. However the higher the diversity of gut bacteria, the better the host’s health.

When the microbiome is out of balance and not working properly, it is called Dysbiosis. This can be caused by not feeding the microbes properly or by taking anti-biotics; lifestyle issues such as stress and sleep also play a role.

The single biggest issue for the colon critters is the Western diet. Our microbiome hates highly processed foods because they don’t contain any fibre and because they nutrients have been broken apart and we can’t use them effectively.

If you want a healthy microbiome that’s producing lots of short chain fatty acids and keeping everything sweet deep inside you, then the first thing you’re going to have to do is look at what you eat. It is very clear that the manufacturing processes used to make ultra processed foods and fast foods negatively affect the microbiome – and hence human health – but science is only just starting to work out how and why.

What is known that obesity is directly related to alteration in the microbiome–immunity–inflammation axis, and that fibre intake can mediate obesity.

*Heart Disease, coronary artery disease, colon cancer, diabetes, high blood pressure, dementia and stroke.

What can the microbiome influence in our body?

Allergies

Your gut bacteria are responsible for “teaching” your immune system how to tolerate dietary proteins and environmental allergens such as pollen and dust mites. When the gut microbiota is disrupted, this teaching process is impaired and the body has a negative reaction to allergens, resulting in food and environmental allergies.

Autoimmunity.

In addition to influencing autoimmune diseases directly linked to the gut, such as Crohn’s disease and ulcerative colitis, emerging research shows that the gut microbiota also affects the development of non-intestinal autoimmune disorders, including lupus, multiple sclerosis, and type 1 diabetes.

Bone Health

Two of the underlying causes of skeletal issues, such as osteoporosis, are inflammation and nutrient deficiencies. Studies show that, by regulating the body’s inflammatory balance, gut microbes can either promote or inhibit bone loss. A healthy gut microbiome also enhances the absorption of critical bone-building nutrients, including vitamins D and K2, calcium, and magnesium.

Joint pain

A balanced microbiome is critical to keeping inflammation down, and arthritis is an inflammatory disease.

Brain Function

The gut microbiome influences the brain and neurobehavior via the gut-brain axis, a network of neurons and signalling molecules linking the enteric nervous system of the gut with the central nervous system. Disruptions of the gut microbiome are implicated in autism, ADHD, neurodegenerative diseases, anxiety, and depression. Conversely, restoration of a healthy gut microbiome with prebiotics and probiotics may alleviate symptoms of neurobehavioral and neurodegenerative diseases. These findings strongly suggest that the gut microbiome is a modifiable factor in the development of brain disorders.

Cancer

It seems the gut microbiome may play a critical role in the development of certain cancers, particularly breast and colon cancer. New research indicates that a person with a healthy gut biome will respond better to immunotherapies.

Cardiovascular Disease

Cardiovascular disease is the leading cause of death worldwide. There are several ways that gut bacteria may influence cardiovascular health.

Gut dysbiosis causes bacteria to move into the bloodstream, initiating an inflammatory response that triggers the growth and build-up of arterial plaque (atherosclerosis), which can cause heart attack and stroke. These plaques have been found to contain bacterial DNA identical to that present in the gut, further supporting the notion that gut microbe-induced inflammation contributes to cardiovascular disease.

An unhealthy gut microbial composition is associated with high blood pressure, a risk factor for cardiovascular disease.

An unhappy microbiome can produce some unwanted metabolites including trimethylamine-N-oxide (TMAO), uremic toxins, and lipopolysaccharide (LPS). TMAO can promote inflammation leading to problems in your cells. Uremic toxins are produced by gut microbial metabolism of amino acids and cause vascular smooth muscle cell calcification (which leads to hardening of the arteries), atrial fibrillation, and cardiac cell dysfunction.

Diabetes

Gut microbes may promote type 1 diabetes by inducing a pro-inflammatory immune response that damages insulin-producing pancreatic beta cells.

Several studies have shown that in people with Type 2 Diabetes, the gut can be overtaken by opportunistic (bad) pathogens crowding out the good microbes that produce beneficial anti-inflammatory compounds. The resulting gut dysbiosis allows the leakage of harmful bacterial metabolites into the circulation, inducing chronic inflammation, an important underlying cause of type 2 diabetes.

Gastrointestinal Health

Not surprisingly, gut microbes play pivotal roles in the development and progression of gastrointestinal disorders, including irritable bowel syndrome (IBS). People with IBS often have an abundance of pro-inflammatory bacteria

Patients with IBS often have gastroesophageal reflux disease, or GERD, and vice versa, suggesting a gut bacterial issue underlying both conditions.

Immunity

Metabolites of beneficial gut bacteria, such as short-chain fatty acids, promote the development of a robust immune system. Gut dysbiosis may impair the immune response, increasing the likelihood of gastrointestinal infections and respiratory infections.

Obesity

Gut microbiome imbalance is associated with an increased risk of being overweight or obese. Dysbiosis may promote obesity by increasing the amount of energy (calories) obtained from the diet, by proincreasing appetite, and by inflaming the nervous system, leading to impaired satiety mechanisms.

Skin

Gut microbes influence the health of our skin by sending signals to the skin that influence inflammation and sebum production, ultimately impacting the development of skin disorders.

Psoriasis patients also harbor dysregulated gut microbiomes and elevated levels of pro-inflammatory cytokines, which may be caused by bacteria moving from the gut into the bloodstream.