Microbiome: Where does the bacteria in your gut microbiome really come from, and does it matter?

Imagine a remote island, recently formed by volcanic activity, in the middle of the ocean. At first, it is lifeless, but a growing variety of plants take hold, providing food for pioneering animal species, until eventually there is a diverse and flourishing ecosystem.

This is a useful way to think about how our gut ecosystems develop. “Your microbiome goes on a journey,” says Alan Walker at the University of Aberdeen, UK. “When you’re born, some bugs get in and then, when you start eating solid foods, other bugs replace them. There’s a dynamic process where your microbiome changes until you get to mid-to-late childhood. Then, through adult life, you’ve got a reasonably stable microbial community.”

Does a C-section affect a baby’s microbiome?

The first individuals that colonise an island can have long-lasting influences on its ecosystem, an idea known as the founder effect. Until recently, the thinking went that if the founder bacteria in a baby’s gut were unusual – because the baby was born by Caesarean section, for instance – this might disrupt their bacterial ecosystems. This idea has led some parents to take radical steps to get their children’s microbiomes back on the right track. But the science behind these ideas is far from settled.

One of the first to document the differences between the gut bacteria of babies born by C-sections and those born vaginally was Maria Gloria Domínguez-Bello at Rutgers University in New Jersey. Her research team found that when babies born by C-section …