Young people are most likely to become obese between the ages of seven and 11 years.
This is according to research conducted by the universities of Bristol, Stirling and Strathclyde, which monitored 5,000 children during their early years.
Professor John Reilly of the University of Strathclyde commented: "This research gives us an important insight into the stages of childhood and adolescence when the environment is most obesity promoting."
The results showed that 19 per cent of the children changed from a healthy weight to being overweight or obese between the ages of seven and 11.
Meanwhile, just ten per cent saw their health deteriorate in this way between three and seven years and seven per cent became overweight or obese between 11 and 15 years.
Professor Debbie Lawlor of the University of Bristol suggested that the findings could be used to target childhood obesity prevention in mid to late childhood.