A woman's diet during pregnancy can alter the function of her baby's DNA in the womb, increasing its risk of obesity, heart disease and diabetes in later life, an international study has found.
Researchers said the study provided the first scientific evidence linking pregnant women's diet to childhood obesity, with important implications for public health.
''This … gives us the potential to work out the optimal diet a mother should eat,'' said Peter Gluckman of the Liggins institute at Auckland University.
The study, conducted by scientists in Britain, New Zealand and Singapore, showed that what a mother ate during pregnancy could change the function of her child's DNA through a process called epigenetic change.
Children with a high degree of epigenetic change were more likely to develop a metabolism that ''lays down more fat'' and become obese. Such children were about three kilograms heavier than their peers by the time they were aged six to nine, Professor Gluckman said.
''That's a hell of a lot of extra weight at that age,'' he said, adding that the extra fat was likely to be carried into adulthood, raising the chances of diabetes and heart disease.
The researchers used umbilical cord tissue to measure the rate of epigenetic change in 300 babies, then examined whether it was linked to the children's weight when they were aged six to nine.
''The correlation was very strong. We didn't believe it at first, so we replicated it again and again,'' Dr Gluckman said.
He said the rate of epigenetic change was possibly linked to a low carbohydrate diet in the first three months of pregnancy.
One theory was that an embryo fed a diet containing few carbohydrates assumed it would be born into a carbohydrate-poor environment and altered its metabolism to store more fat, which could be used as fuel when food was scarce.
Dr Gluckman said the study, which will be published in the journal Diabetes next week, confirmed long-held suspicions that poor pre-natal nutrition could have a significant impact on adult heath.