Factors that determine whether or not a child will be obese are usually set in place by the age of two, according to recent US research.
The researchers found that, if a child gains too much weight in infancy, it passes a critical level of body fat that can stay with it into adulthood.
The finding makes it clear that there is a "tipping point" for childhood obesity that relates to the eating preferences babies pick up from the way their parents feed them.
For the study, the researchers surveyed 111 children, all of whom had a very high body mass index.
They also looked at 480 medical records at a private medical practice and a teaching hospital, 184 of which were eventually included in the study.
They found that 90% of the children whose weight had increased most rapidly in infancy were overweight by age 5.
John Harrington of Eastern Virginia Medical School said that doctors and parents should put a lot of thought into their child's weight, even when they are still only several months old.
Doctors should be aware that they need to measure the rate by which babies gain weight according to objective standards.
The difference between a healthy baby and an unhealthy baby may simply be that an unhealthy baby rapidly becomes more and more chubby, while a healthy baby comes to a stable weight.
All of the 111 children who participated in the study became overweight by the age of 10.
The reason why childhood obesity develops in some cases and not in others is complex, and probably has to do with a combination of dietary preferences, as well as a lack of exercise.
Harrington said that doctors often waited until medical complications arose in people before they began treatment.
He said that getting parents and children to change well-established habits was a monumental task, and that people could alter the obesity epidemic by addressing inappropriate weight gain early in infancy.
The study authors said that it was untrue that chubby babies were always healthy, and that only 20% to 50% of overweight children were regularly diagnosed.
