Two nurses deliver a baby by caesarean section Babies born by caesarean section are at greater risk of becoming obese in  later life than those delivered naturally, researchers have found. The obesity epidemic could be partly driven by rising rates of surgical deliveries, although the reasons for this are unclear, their study suggests.
The report, in the American Journal of Clinical Nutrition, says  lack of exposure to beneficial bacteria in the birth canal could explain the link.
However, the children of fatter mothers are also more likely to have weight problems.
Given that obesity in pregnancy is a risk factor that leads to more caesarean section births, it may be that this relationship between the weight of mother and child explains the findings.
In the study, Brazilian researchers looked at obesity rates in 2,000 people aged 23 to 25.
They found 15 per cent of those delivered by caesarean were obese compared with 10 per cent of those born naturally.
The study analysed a number of factors that might explain the connection, including heavier birthweight, income and education levels, because women with more qualifications had a higher caesarean rate.
But even after accounting for these factors, being born by caesarean was linked to a 58 per cent increase in the risk of obesity in adulthood.
Dr Helena Goldani, who carried out the study with colleagues at the Universidade Federal de Rio Grande do Sul in Porto Alegre, said the findings did not prove a causal link between surgical  deliveries and weight problems.
But she explained that, because infants born surgically are not exposed to beneficial bacteria  in the birth canal, they might  take longer to accumulate good bugs which affect the metabolism.
Obese adults tend to have fewer of these friendly bacteria in their digestive tract than normal-weight people.
The theory is that having fewer good intestinal bugs leads to the body burning fewer calories and storing more of them as fat. But other experts said there was a ‘huge gap in the data’.
They said it was difficult to interpret the study because it did not include any information on the mother’s weight while pregnant.
Dr Ian Campbell, medical director of Weight Concern, said the study ‘raises more questions than it answers’.
He said: ‘This is a very interesting finding, which is difficult to interpret without knowing the weight of the mothers while pregnant.
‘However, women who have a caesarean are less likely to breastfeed, which helps prevent obesity in children by establishing a healthier weight in childhood.’
‘There are many different ways of influencing obesity in adulthood and this is another area for research,’ he added.
Around 23 per cent of all  births in the UK are by caesarean  section. The World Health Organisation recommends the figure should be around 15 per cent.
Brazil, where the study was done, has around 44 per cent of babies delivered by caesarean section. Many of those procedures are thought to be medically unnecessary.