You probably think of your gut as the place where food goes in, nutrients get absorbed, and waste comes out. Fair enough, that is what we were all taught in school.
But your gut microbiome, the 38 trillion or so bacteria, fungi and other microorganisms living inside your intestines, is doing a great deal more than breaking down your rajma chawal. It shapes your immune system, your weight, your mood, and even how well you sleep at night. Your gut works less like a pipe and more like a second control centre for the rest of your body.
~38 trillion
microbes living in your gut
~70%
of your immune system sits here
~90%
of serotonin is made in the gut
100M+
Indians now live with diabetes
It digests far more than you could alone
Digestion is the obvious one, but even here your bacteria do work your body cannot. Species like Bacteroides thetaiotaomicron break down the complex plant fibres in sabzi, dal and whole grains into molecules you can actually absorb. Without them, much of the fibre you eat would simply pass through, unused.
Certain bacteria also ferment that fibre into short-chain fatty acids (SCFAs) like butyrate, propionate and acetate. Butyrate in particular is the primary fuel for the cells lining your colon. So the bacteria eat your leftover fibre, and in return, they feed the wall of your gut.
The bacteria eat your leftover fibre, and in return they feed the wall of your gut. It is a pretty elegant arrangement.
It trains your immune system
About 70% of your immune system lives in and around your gut, in a network called the gut-associated lymphoid tissue (GALT) that sits just beneath the lining, constantly sampling what passes through. Beneficial species like Lactobacillus rhamnosus and Bifidobacterium longum help calibrate this system — teaching it the difference between a harmless food protein and a real pathogen.
When your microbiome is diverse and balanced, your immune system tends to respond proportionally. When it is not, you get overreaction (allergies, autoimmune flares) or underreaction (frequent colds, slow recovery).
Why does one person catch every cold in the office while another barely sniffles? Part of the answer is living in their gut.
Your metabolism is partly microbial
Ever wonder why two people can eat the same food and end up with different results? One well-known finding involves the ratio of Firmicutes to Bacteroidetes. Higher Firmicutes proportions have been linked with greater calorie extraction — some microbial mixes are simply more “efficient” at harvesting energy, which means more calories stored than you needed.
Then there is inflammation. When the gut barrier weakens, bacterial fragments called lipopolysaccharides (LPS) leak into the bloodstream and trigger chronic low-grade inflammation, which interferes with insulin signalling and fat storage. In a country where more than 100 million people live with diabetes, that mechanism matters more than most people think.
Curious which bacteria are running your own metabolism? Take the BioMeBar gut assessment →
Your gut talks to your brain — and the brain listens
Your gut and brain are in constant conversation through the gut-brain axis, and the main highway is the vagus nerve. The signal is not only electrical; your gut bacteria actually produce neurotransmitters. About 90% of your body’s serotonin, the molecule most tied to mood, is made in the gut, not the brain. Other microbes make GABA (calming) and dopamine (reward and motivation).
About 90% of your body’s serotonin is made in your gut — not your brain.
This is why gut trouble and mental-health symptoms so often travel together. People with IBS have markedly higher rates of anxiety and depression; chronic stress frequently shows up as digestive symptoms. There is even emerging work on sleep: certain gut bacteria influence melatonin and circadian rhythm. If your sleep goes haywire when your digestion is off, your microbiome may be part of the reason.
What this actually means for you
So your gut microbiome is not just about whether you feel bloated after lunch. It is a biological system that touches your immunity, your metabolism, your mental health and your digestion, all at once. When it falls out of balance, the effects show up in places you would never connect back to your gut.
“But do I really need to test my gut?”
Not everyone does. But if you have been chasing the same symptoms for months (bloating, low energy, mood dips, stubborn weight), guessing gets expensive and slow. Seeing your actual microbiome composition turns trial-and-error into a targeted plan.
Stop guessing. See what is actually in your gut.
BioMeBar profiles your unique microbiome and personalises recommendations to what is genuinely there, because with trillions of organisms running your biology, one-size-fits-all does not make sense.
References & Further Reading
Sender R, Fuchs S, Milo R. Revised estimates for the number of human and bacteria cells in the body. PLoS Biology, 2016. (≈38 trillion bacterial cells.)
Ley RE, Turnbaugh PJ, Klein S, Gordon JI. Human gut microbes associated with obesity. Nature, 2006;444:1022–1023. (Firmicutes/Bacteroidetes and energy harvest.)
Cani PD, et al. Metabolic endotoxemia initiates obesity and insulin resistance. Diabetes, 2007;56:1761–1772. (LPS, gut barrier and inflammation.)
Yano JM, et al. Indigenous bacteria from the gut microbiota regulate host serotonin biosynthesis. Cell, 2015;161:264–276. (Gut-derived serotonin.)
Anjana RM, et al. Metabolic non-communicable disease health report of India (ICMR-INDIAB). The Lancet Diabetes & Endocrinology, 2023. (≈101 million Indians with diabetes.)
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