Over half your body isn't human

In the classic 1966 science-fiction film Fantastic Voyage, doctors are shrunk to a microscopic size and injected into a man to save him from a life-threatening ailment.

Now real-life scientists are discovering that the inside and outside of our bodies are teeming with millions of micro-organisms that, like Hollywood’s mini-medics, may play a beneficial role in human health.

Experts say it is probable that more than half of our bodies consist of non-human mini-invaders in the form of trillions of microbial cells and the genes they hold.

This mass of mini-lifeforms has been named the microbiome and it is changing how we look at health and even what it means to be “us”. Because, according to some estimates, only 43% or the cells in our body are actually “human”.

The Nightingale effect

For many years, science has focused on how to stop harmful bacteria, viruses and other small organisms that live on our skin and in our stomachs from making us ill.

Florence Nightingale’s work on sterilizing medical equipment in army hospitals and the development of antibiotics such as penicillin are two examples of how we have tried to use scientific knowledge and improvements to control their unwanted side-effects of germs.

But the microbiome is a huge ecosystem of complex organisms, including bacteria, yeasts, fungi, viruses and protozoa that can weigh up to 2kg in each human.

Experts say this bundle of micro-organisms has a beneficial influence on many aspects of our health, from conditions such as obesity and rheumatism, to mental illnesses including depression. They also argue the microbiome should be classified as a human organ and are seeking to discover how we can better use microbiomes to improve our well-being.

The good, the bad and the healthy

“They are essential to your health,” Ruth Ley, the director of the department of microbiome science at the Max Planck Institute in Germany, told the BBC. “Your body isn’t just you.”

The terms “good bacteria” and “bad bacteria” have been around for a while, but evidence is emerging that the way people in industrialized societies live could be actively harming their microbiomes. And the very antibiotics that we have developed to keep harmful bacteria at bay also damage those that keep us healthy.

“Gut bacteria are involved in harvesting energy from food, balancing the good versus bad bacterial composition, manufacturing neurotransmitters such as serotonin, enzymes and vitamins like vitamin K and are involved with immune and metabolic functions,” said an article in the Journal of Cardiovascular Nursing.

Too clean?

Changes in the diets of Western, industrialized populations have led to less-diverse gut microbiomes compared to people from more rural and less developed populations, the article writers say.

They point to research that indicates people in developed nations may be too clean, saying: “A general shift away from natural environments with little exposure to soil, animals and other environmental microbes seems to be impacting the gut microbiome in potentially detrimental ways.

“Children raised in homes with pets have less risk of allergic diseases and new evidence is demonstrating a link with gut microbiome patterns. Exposure to dogs seems to alter the gut microbiome to be protective against allergic airway issues and respiratory viruses.”

Natural healing

Meanwhile, experiments have shown that if faecal bacteria from obese and thin humans are transplanted into mice, then the animals become either fatter or thinner, depending on whose bacteria they received.

Recent evidence from animal and human models suggests transferring faecal bacteria from thin to overweight people could be used as a therapeutic intervention to combat what is a very real health emergency around the world.

Researchers are also investigating whether a better understanding of our microbiome can provide cures for other conditions, ranging from irritable bowel syndrome to cancer. Experts are even examining hospitals in an attempt to discover if their very cleanliness could be a cause of why so-called superbugs like MRSA can afflict patients after operations

Jack Gilbert, an environmental microbiologist at Argonne National Laboratory in Illinois in the US, said in a 2014 interview: “For the past 150 years, we’ve been literally trying to just kill bacteria. There is now a multitude of evidence to suggest that this kill-all approach isn’t working.

“We’re now trying to understand that maybe, just maybe, if we could cultivate non-pathogenic bacteria on hospital surfaces, then we could see if that would lead to a healthier hospital environment.”