Gut Bacteria in Urban Indians Linked to Rising Diabetes and Obesity, Study Finds
A new study suggests that changes in gut bacteria, driven by urbanisation and dietary shifts, may help explain the rising rates of diabetes, obesity, and hypertension among urbanising Indians. The research, published in the peer-reviewed journal Gut Microbes, presents the first reference database of the gut microbiome across South Asia, based on samples from 575 adults in 10 communities across India and Sri Lanka.
India is home to an estimated 89.8 million adults with diabetes as of 2024, the second-highest burden globally after China, according to the International Diabetes Federation. The federation projects that number could rise by 75% to 156.7 million by 2050, with 43% of current cases undiagnosed. The rapid increase is largely attributed to urbanisation and changing diets.
To isolate the effects of environment from genetics, researchers paired remote, forest-dwelling or early-agriculturalist communities with relatives who had moved to towns and cities where processed foods like pizza, chowmein, and soft drinks are common. Both groups share genetic ancestry, verified by genome sequencing, so differences in gut bacteria are likely due to diet and lifestyle.
One clear finding involves the bacterium Megamonas, which was consistently more abundant in urban participants. Megamonas has been linked to obesity, hypertension, and elevated blood glucose in other studies. The paper reports a significant association with blood glucose and a known mechanism involving lipid absorption. “We are reporting for the first time that Megamonas are thriving because of a change in diet,” said study co-leader Niraj Rai of the Birbal Sahni Institute of Palaeosciences, Lucknow.
In contrast, the bacterium Holdemanella, associated with fibre intake and glucose tolerance, was found to be prevalent in rural populations but lost with urbanisation. An exception was in Kerala, where many communities maintained traditional diets even after migrating.
Rai emphasised that urbanisation in this context is more about food processing than meat consumption. In northeastern India, both rural and urban groups eat meat, but urban diets include biscuits, soft drinks, and occasional pizza.
The study also challenges long-standing theories about dairy consumption in South Asia. The lactase-persistence gene, which allows adults to digest milk, is often traced to migrations from northwest regions around 4,000–5,000 years ago. However, the researchers found that pastoral communities such as Ladakhis, Toda, Kota, and Kadu Golla, who consumed milk much earlier, carry gut bacteria capable of breaking down lactose. Screening over 10,000 samples showed little correlation with lactase-persistence genotypes, suggesting that the mutation was an additional benefit, not a requirement, and that bacteria were positively selected over generations.
Gut microbiome research is important because these bacteria act as environmental factors that modify how genes are expressed, potentially influencing disease risk. The study offers a clearer picture of how rapid urbanisation is reshaping the health of populations in India and beyond.
