How Cities Change the Bacteria Inside Us

South Asian cities are reshaping the tiny world inside our guts in ways that differ from place to place. A large study called SAMBAR looked at 575 adults from ten communities that live in both remote villages and bustling towns. The researchers compared the gut bacteria of people who still practice traditional lifestyles with those who have moved to modern urban settings. The findings show that the gut bacteria in these communities are quite distinct from those seen worldwide. They cluster more strongly by where people live and the culture they belong to than by whether they are urban or rural.

When people change from a village life to city life, the gut bacteria shift in patterns that depend on their community. In some groups, new bacterial groups linked to wheat and dairy appear, which might help people who cannot digest lactose. At the same time, markers of urban living are tied to higher levels of bacteria that have been linked with disease. One such group, called Megamonas, is more common in the SAMBAR samples and is associated with higher blood sugar and less bacterial diversity. These changes are not uniform across the region. Even neighboring towns can have different bacterial responses to urbanization, reflecting local habits and geography. The study highlights that health effects of city life on gut bacteria must be studied in each community separately.

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