The second genome by Dai Eun Greer

For decades, healthy eating has been sold as though it were a universal equation. Eat more fibre. Avoid saturated fat. Choose whole grains. Fill your plate with colourful vegetables. While these recommendations have undoubtedly improved public health, they have also created one of modern nutrition's most persistent myths: that the same food will produce the same benefits for everyone.

The science of the human microbiome is steadily dismantling that comfortable assumption. Hidden inside each of us is an ecosystem of trillions of bacteria, fungi and other microorganisms that collectively contain far more genes than our own DNA. If our genetic code is the blueprint we inherit, our microbiome is the blueprint we negotiate throughout life. It may well be our true "second genome."

This changes the conversation about nutrition in profound ways. Two people can sit at the same breakfast table, eat identical bowls of oatmeal topped with blueberries, and experience remarkably different biological responses. One person's blood sugar remains stable while another's spikes dramatically. One feels energetic for hours, another reaches for a snack before noon. The difference may not lie in willpower, metabolism or age. It may lie in the invisible society living inside their digestive tract.

That reality should make us deeply sceptical of nutritional absolutism. Every few years a new dietary movement arrives proclaiming salvation through keto, veganism, carnivore eating, intermittent fasting or the latest superfood imported from some remote mountain valley. Yet the microbiome stubbornly refuses to cooperate with fashionable certainty. What nourishes one internal ecosystem may barely register in another.

Perhaps the greatest irony is that modern life has quietly impoverished this second genome. Highly processed foods, excessive antibiotic use, sanitised environments and monotonous diets have reduced microbial diversity across much of the developed world. We have become obsessed with sterilising our surroundings while inadvertently sterilising parts of ourselves. The result may not simply be digestive discomfort but altered immunity, inflammation, mental health and metabolic disease.

This should not become another excuse for nutritional chaos. The microbiome is not a licence to declare that doughnuts are secretly healthy because someone somewhere digests them efficiently. Rather, it reminds us that biology is more nuanced than ideology. General principles still matter, but individual variation matters almost as much.

Medicine is already moving towards personalised treatments based on genetics. Nutrition will almost certainly follow the same path. Instead of prescribing identical diets for millions, future healthcare may analyse an individual's microbial composition before recommending foods likely to improve blood sugar control, reduce inflammation or even influence mood. That prospect is both exciting and humbling because it admits that human beings are less standardised than nutritional guidelines often pretend.

The microbiome also delivers a philosophical lesson. We like to imagine ourselves as autonomous individuals making rational dietary choices. In reality, we are walking ecosystems whose health depends on countless microscopic partners we cannot see. Their success often determines our own.

Perhaps the greatest dietary revolution will not come from discovering another miracle food. It will come from abandoning the comforting fiction that there is one perfect diet for everyone. Our second genome is quietly reminding us that health is not only written in our DNA but negotiated every day with the invisible civilisation we carry within us.