CHICAGO (Reuters) - Children who start putting on fat before the age of five are more than twice as likely to turn into obese adults as those who don`t, according to a study published on Monday. The finding was based on a survey of 390 U.S. children born between 1965 and 1971 who were monitored into adulthood. Researchers at Children`s Hospital Medical Center in Cincinnati, and other U.S. institutions which collaborated on the study, said children tend to become thinner until around the ages of five or six, when they start adding fat. The point when the turnaround occurs is called the "adipose rebound." In the study, children who reached that point before their fifth birthday were more than twice as likely to become obese adults, regardless of whether they had overweight parents. The report suggests that the age at which the turnaround point occurs may be difficult to change, but could be influenced by environmental factors such as parents urging children to eat at a time when there is natural tendency for them to be losing fat. It suggests that future research should explore whether the turnaround point can be delayed and whether that would also change the risk of adult obesity. Another report says the prevalence of children and adolescents who are overweight has increased dramatically in a relatively short period of time and mirrors trends also found in Europe. Part of the problem, it says, is a sedentary lifestyle in which television and video games take the place of exercise.