WELLINGTON - AN EXPECTANT mother's diet during pregnancy can alter 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 major implications for public health. 'This a a major breakthrough because for the first time it gives us the potential to work out the optimal diet a mother should eat,' Professor Peter Gluckman from Auckland University's Liggins Institute told AFP.

'That's likely to vary slightly from mother to mother, but it could be a major tool in addressing the obesity epidemic.' 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, researchers found. Such children were around three kilograms heavier than their peers by the time they were aged six to nine, Prof 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 developing 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,' Prof Gluckman said.

The study found the effect was not linked to either the mother or the baby's weight at birth, meaning a slim woman could deliver a small baby which still went on to became obese because of changes triggered by diet in the womb.