Our guts are home to tens of trillions of microscopic organisms – bacteria, fungi, and viruses – whose role is increasingly being recognised as responsible for our overall health.
These microorganisms, which are collectively called the gut microbiome, have come to be known for the role they play in the body’s nutrient and drug metabolisms, in the maintenance of structural integrity of our guts, in the modulation of the immune system and in protecting us from pathogens.
Researchers estimate that between 10 to 100 trillion individual organisms live in our gut – which spans from the oesophagus to the rectum – and these have developed symbiotic relationships with us humans over millions of years.
With an estimated 1,000 different strains of bacteria, the gut microbiome is understood to contain nearly 100 times more genetic material than the human genome. Several researchers and scientists are of the opinion that the gut microbiome should be treated as a separate organ in the body, given the outsized effect it has on many aspects of our health.
The gut microbiome is a complex and dynamic population of microorganisms that have a marked influence on homeostasis and disease (homeostasis is the self-regulating process of the body to maintain stability while adjusting to environmental changes). Researchers have figured out that there are various environmental factors that affect the make-up of the microorganisms in our guts, but none are more important than the food that we eat.
This understanding has opened the door to efforts for developing futuristic therapies for several conditions like inflammatory bowel disease, metabolic conditions such as type 2 diabetes, obesity, immune disorders, mental health issues and much more.
The holy grail for treatment will include modulation of the gut microbiome through food, rather than any medication. While several types of microbes make up the microbiome, bacteria are understood to make up the largest chunk of these organisms, with their functioning being by far the best understood.
And despite being a relatively new field of study, the gut microbiome has been linked with heart health, gut health, immune disorders, behavioural disorders, cancers and much more. This has spurred researchers to modulate the gut microbiota to potentially treat such diseases; In fact, several such treatment efforts have shown good results in animal and human models.
How the gut microbiome affects our body
Research has shown that our first interaction with gut microorganisms happens when, as babies, we pass through our mother’s birth canal. Scientists have found that “babies born vaginally have different gut bacteria than those delivered by the caesarean section”, and while the role of these bacteria is not fully understood, it is theorised that they help in the digestion of mother’s milk.
The gut microbiome of a child is understood to fully develop by age three, making it important for it to receive a balanced and nutritious diet before it reaches this age. As our understanding of the microbiome grows, more thought is being given to the gut health impact of prescribing antibiotics or medications to children.
As we mature, our gut microbiomes begin to affect our immune systems, where these microbes communicate with immune cells and tell them how to respond to infections. Research suggests that the community of microorganisms in our guts influences the susceptibility to many immune-related diseases.
The microbiome also affects the brain through the central nervous system in what is called the gut-brain axis. It is understood that some microbes in our guts produce short-chain fatty acids and neurotransmitters such as serotonin, dopamine or their precursors, that in turn affect moods and drive other psychological and neurological changes.
Other research has shown how gut bacteria feed on the fibre from the food that we eat (prebiotics), in turn helping to generate amino acids, vitamins, neurotransmitters and hormones. These play an important role in other realms of our health.
What is driving research in this area?
Research into the gut microbiome has received a massive boost with advancements in synthetic biology, biomaterials engineering and traditional microbiology. One of the biggest factors holding back research into microorganisms in our guts has been the anaerobic nature of most gut bacteria (i.e., they don’t need oxygen to survive), making it hard to study them outside the body.
Advances in the last few decades on this front, along with the proliferation of next-generation sequencing techniques, have made it possible to understand the composition and functioning of organisms in our guts. But it is still a challenge given the vast number of microorganism strains and their variability across populations.
Moreover, one of the big unknowns that scientists are today trying to understand is the community dynamics of these microorganisms, and how environmental factors affect the role some microbes play in the gut. Studying individual organisms and their roles might not be ideal as it does not account for the fact that these organisms could also work together, apart from working with us.
The selective modulation or ‘engineering’ of the human microbiome is being seen as a path to cure diseases. The understanding of the way the gut functions could lead to improvements in probiotics, prebiotics, antibiotics and several other therapies for disorders that today rely on medication — that is often blamed for its adverse effects on our body and mind.
