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Journalism of Courage
Picture this: Trillions of microscopic organisms inhabiting your body at this very moment! Treat them not as intruders but companions that influence how we digest our breakfast and think and feel each day. This community of bacteria, fungi and other microbes, collectively called the gut microbiota, was once regarded as peripheral to human health. For much of modern medical history, their role was thought to be limited to digestion. Yet in the past decade scientists have realised these little organisms have a direct line of communication with our brain.
Research now shows that they are in constant communication with the brain, shaping not only how we process food but also how we think, feel and age. This communication, also called the gut-brain axis, relies on nerve signals travelling through the vagus nerve, chemical messengers such as serotonin and other metabolites, as well as immune responses triggered in the gut. When the microbial community is balanced, the system supports health but when the balance of this system is disrupted — a condition known as dysbiosis — it can spark inflammation, disturb brain chemistry and set the stage for neurodegenerative disease.
The idea that health begins in the gut is not new. More than two millennia ago, Hippocrates declared that “all disease begins in the gut.” In the early 20th century, Russian Nobel laureate Élie Metchnikoff noted that Bulgarian who consumed large amounts of yogurt appeared to live longer, proposing that the “friendly bacteria” in fermented foods played a protective role. Some physicians of that era even speculated that toxins from harmful microbes might leak into the bloodstream and affect mood or mental clarity—a crude but surprisingly prescient guess.
The decisive shift came in 2008 with the launch of the Human Microbiome Project, which provided the tools to map the trillions of organisms inhabiting the body. This breakthrough revealed the diversity of the gut ecosystem and its influence on immunity, metabolism, and brain function. Since then, studies have uncovered striking links between gut imbalances and conditions such as Alzheimer’s and Parkinson’s.
In Alzheimer’s disease, people with early memory problems often show fewer bacteria that produce anti-inflammatory compounds and more microbes that drive inflammation. This imbalance appears to accelerate the buildup of amyloid-β plaques — sticky protein clumps that kill neurons. One recent study showed that propionate, a short-chain fatty acid produced by gut bacteria, can slow the buildup of amyloid-β plaques and dampen inflammation in Alzheimer’s animal models, pointing to microbial metabolites as potential protectors of the ageing brain.
Parkinson’s disease provides another compelling case of the disease beginning in the gut. Long before tremors appear, patients often display disrupted microbial communities: fewer protective species and more that fuel inflammation. These changes are thought to trigger the misfolding of a protein called alpha-synuclein in the gut, which then travels along the vagus nerve to the brain and begins damaging nerve cells.
New evidence suggests the story may have broader implications: bacteria normally confined to the mouth have been found migrating into the gut of people with Parkinson’s, where their presence correlates with cognitive decline, hinting at a possible correlation between microbial shifts and Parkinson’s as early markers of disease progression.
These discoveries are important not only because they help explain how neurodegeneration may begin but also because they point to possible ways of prevention and treatment. Probiotics, the live “friendly” bacteria taken as pills or drinks, have already shown modest benefits in trials, easing anxiety and improving memory in people with mild cognitive decline. In Parkinson’s patients, probiotics have been found to improve digestion and help medications work more smoothly.
Diet, however, appears to be the stronger lever; a Mediterranean-style diet rich in fruits, vegetables, whole grains, nuts and olive oil supports protective microbes, and long-term studies link such diets to slower cognitive decline. Prebiotic fibres in foods like onions, garlic, oats, and bananas act as fuel for beneficial bacteria, encouraging them to produce compounds that calm inflammation before these can harm the brain.
More experimental strategies, like faecal microbiota, in which microbes from healthy donors are transferred to patients are also under investigation. Though still in its early stages, research in animals has shown that it can reduce toxic brain proteins and improve motor function. Early human trials are now underway.
Recent scientific studies reveal that the composition of gut microbiota is highly responsive to diet and lifestyle. Diets rich in complex carbohydrates and dietary fibre increase the abundance of beneficial bacteria such as Bifidobacteria and Lactobacilli which produce short-chain fatty acids essential for reducing inflammation and maintaining gut barrier integrity. In contrast, diets high in processed foods and refined sugars decrease microbial diversity and promote pro-inflammatory species.
In India, the most accessible way to get a snapshot of gut microbiota is through stool-based tests offered by private diagnostic labs and a few emerging biotech startups. These tests usually rely on DNA sequencing to identify the bacterial species present and assess microbial diversity as well. Companies in cities such as Bengaluru, Hyderabad and Delhi now offer at-home sample collection kits, though the detailed and clinical interpretation can vary widely.
For most people though, practical cues remain important: chronic digestive discomfort, frequent antibiotic use, or unexplained inflammation can be signals of an imbalance. In such cases, physicians in India typically recommend dietary changes first—greater fibre intake, fermented foods such as curd, idli, or dosa, and reduced processed sugar—before recommending probiotic supplements or advanced microbiome testing
Lifestyle factors beyond diet also play a decisive role. Regular exercise and adequate sleep help sustain microbial balance whereas chronic stress doesn’t. Similarly, unnecessary antibiotic use can disrupt commensal communities, sometimes allowing opportunistic pathogens like Clostridioides difficile to dominate. Collectively, these findings highlight that the microbiota is not static; it responds dynamically to external factors, influencing not only digestion but also immune regulation, metabolic function, and even brain health.
One message is already clear: the health of our gut microbes profoundly influences the health of our minds. Paying attention to diet, nurturing beneficial bacteria, and keeping the microbial ecosystem in balance may turn out to be one of the simplest and most effective ways of protecting the brain as we age.
(Prof V S Chauhan is a former director and now Arturo Falaschi Emeritus Scientist at the Delhi-based International Centre for Genetic Engineering and Biotechnology)
