A CAUSAL link involving friendly stomach bacteria has been found between C-section births and increased obesity risk.

Scientists had already shown that Caesarean babies are more likely to grow up obese, but have not been clear about the reason why.

In 2015, it was estimated that almost one third of babies are born in Scotland by Caesarean section, partly due to more obese or overweight and older mothers.

The new research, conducted on mice, confirms that the weight gain is linked to the impact of C-section birth on gut bugs.

Lead scientist Dr Maria Dominguez-Bello, from New York University School of Medicine, who led the research, said: “Our study is the first to demonstrate a causal relationship between C-section and increased body weight in mammals.”

The team compared 34 mice delivered by C-section with 35 animals born naturally while following their weight changes and analysing intestinal bacteria.

The make-up of the “microbiome” – bacterial population – in normally born mice evolved normally. C-section mice not only gained weight but also had colonies of gut bugs that did not follow the usual progression path.

They initially matured too quickly before being held back. As in humans born by C-section, gut microbe diversity in the mice decreased through the first year of life.

The study is published in Science Advances.