At this very moment, your gut is filled with almost 100 trillion microbes – mostly
bacteria of 300 to 500 different types! and also fungi, protists and viruses.
That’s twelve thousand, six hundred and fifty-eight times the human population of micro
organisms living inside your body! In fact, there is one bacteria for every human cell. Did you ever
imagine that there is such a huge population of small and tiny creatures living inside you?
But why do we have so many microbes inside us, where did they come from and what do
they do inside us? We’ve only recently started to understand their role in our bodies and they are
far more important than we could’ve imagined. So, where does it all begin?
It all begins in the uterus. The amniotic fluid in the mother’s uterus contains bacteria
and when the foetus swallows some of that fluid, the microbes take a seat in the foetus’s gut.
But, it is only after birth that the microbes begin their colonization.
During the birth, the bacteria present in the mother’s vagina
cover the baby and find their way to the gut when the baby comes out through it. This
is the reason why babies born through a C-section procedure have a different gut microbiota
compared to their naturally born counterparts. The bacteria in the gut comprise a few different
types of characters. Some are neutral, just minding their business in the gut
while being part of a mutually beneficial agreement with the gut.
Some, more worryingly, can cause diseases like cholera, or simply cavities and bad breath.
So how does a newborn deal with all of these disease-causing bacteria? Breast milk.
Breast milk contains antibodies that protect the newborn babies till their
immune systems learn to fight for themselves. Breastmilk also has human milk oligosaccharides.
These are sugar molecules which boost good gut bacteria growth.
It’s a natural prebiotic that helps increase the population
of Bifidobacterium – an important type of bacteria present in a baby’s gut.
Antibodies along with the good bacteria prevent nasty bacteria
from finding permanent abode in the gut. As the tiny human grows up, their body
changes, and so does their food bringing a whole new flavour to the gut microbe’s party.
New foods introduce new microbial residents in the gut where they can mingle with older
residents. The new foods also bring new nutrients that support the growth of diverse gut bacteria.
Post three years of age, the gut and its microbes resemble those of an adult. They are found
throughout the gut, their numbers are highest in the large intestine, especially the colon.
So, we know how they get in, but what are they doing there? And more importantly,
why does everybody keep saying they’re good? These residents interact with our bodies in many
ways. Most importantly they affect our digestion! On an average, 60 tonnes of food passes
through your GI tract through your lifetime! That amounts to eating
ten elephants or a fully fuelled aeroplane. To break complex sugars like starch and other
polysaccharides our bodies don’t have the right enzymes. But gut bacteria do. Their enzymes break
down these sugars to make B group vitamins and vitamin K. The gut bacteria release this into the
intestine where it is absorbed by our own cells. We should thank our gut bacteria as we need these
vitamins for our body to stay healthy. Second, they affect our brain.
Essentially, the gut microbes have our brain on speed dial and they help coordinate our body’s
functions. This is known as the: Gut-brain axis It's the two-way communication between our
central nervous system and enteric nervous systems — the nervous system linked to the
gut — allowing our gastrointestinal tract and our brain to talk to each other. This back and
forth conversation helps our body maintain a physiological balance, a homeostasis.
The gut microbes release certain molecules and hormones that can affect our brain.
Gut bacteria like Corynebacterium feed on the food we eat and produce metabolites like serotonin.
This serotonin is released into our blood and eventually it interacts with our nervous system.
This then signals to the brain affecting our moods and emotions. Still other metabolites are GABA,
a neurotransmitter and butyrate which interact in other ways with the nervous system.
Depending on how healthy our gut bacteria are, it can affect our brain signalling, affecting
our hormonal responses. This is why sometimes when you have indigestion or stomach problems,
you could be feeling a lot of anxiety or irritability.
To know more about the parts of the brain involved in emotions,
check out our video on the limbic system! Your gut bacteria also put you to bed. Certain
gut bacteria release sleep-inducing compounds called muramyl peptides. People with a disturbed
gut bacteria profile tend to have poorer sleep. Your immune system also has your microbes to
thank. Gut bacteria and the immune system collaborate to keep disease causing bacteria
at bay. The immune system matures and learns from which gut bacteria present
and the gut bacteria secrete certain metabolites that further help your defences.
But how do gut bacteria perform such helpful tasks? What gives them so much power?
These bacteria have the genes for it and all these genes make up what we know as the gut
microbiome. Interestingly more than 99% of the genes in our body are microbial.
But how can we increase our good gut bacteria’s strength?
Disease, genetics or lifestyle - such as eating
too much junk food - can mess with our microbial residents causing dysbiosis.
Dysbiosis is nothing but a major imbalance of the types of gut bacteria in the body.
The best thing to do is to try your best to live a healthy conventional lifestyle. A consistent sleep
schedule, exercise, a balanced diet and keeping stress levels to a minimum will do wonders.
There’s also probiotics and prebiotics that help the gut.
Probiotics are good bacteria that we put in our bodies, in numbers high enough
actually to have a beneficial effect. These bacteria can be consumed by taking capsules
or eating probiotic foods like cheese, yogurt and other bacteria rich foods.
Prebiotics are foods with molecules such as inulin,
fructooligosaccharides or galactooligosaccharides that allow the good gut bacteria to grow better.
Do consult your doctor to find what is right for you.
So, the next time you’re procrastinating on going to the gym, or veering towards eating
that greasy pizza, remember, that what you eat and for that, your gut bacteria will be thankful.