Some previous studies have suggested that the odds of other adverse long-term outcomes, such asthma and type-1 diabetes in childhood, are also higher in babies born by caesarean.
The new study by researchers at Imperial College London included data from 10 countries, and found that the average BMI of adults born by caesarean section is around half a unit more than those born by vaginal delivery.
It is the largest to show a link between caesarean delivery and BMI in adulthood.
The authors say they cannot be certain that caesarean delivery causes higher body weight, as the association may be explained by other factors that weren't recorded in the data they analysed.
The study was published in the journal PLOS ONE.