WELLINGTON - New Zealand scientists have helped find a link between a woman's diet during pregnancy and her child's chances of becoming fat.

Professor Peter Gluckman, who led the New Zealand and Singapore arms of the study, said the study proved the path to obesity, diabetes, or heart disease started before a child was born.

"It's a major breakthrough... Frankly, it's the biggest, most important finding I've ever made as the result of 15 years' work," he told New Zealand news agency NZPA.

Findings revealed a mother's diet during pregnancy could alter her child's DNA, through a process called epigenetic change, which could lead to her child putting on extra weight later in life.

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"Now we know that mothers who don't eat balanced diets during pregnancy, their babies are at greater risk," he said.

The international study found there was something in a women's diet, particularly during the first third of a pregnancy, that was of crucial importance.

The study had produced the first data that quantified a link between events before birth and the chance of obesity but researchers found the mother's size and the child's weight at birth had no bearing on that link.

Some doctors and scientists had long suspected a poor start to life played a major role in the later development of heart disease, diabetes and obesity but that view had largely been ignored by policy makers, physicians and public health practitioners due to lack of data, Peter said.

During the study, the team measured the degree of chemical modification of DNA in umbilical cord tissue from nearly 300 children and showed that this strongly predicted the degree of obesity at six or nine years of age.

The researchers were surprised by the size of the effect, children varied in how fat they were but measurement of the epigenetic change at birth allowed the researchers to predict 25 percent of that variation. The association was much stronger than explanations of obesity based on genetics and lifestyle, he said.

There was the potential to halt progression towards disease through nutritional and or pharmacological interventions during early life, he said.

He said a substantial part of the project's success was due to collaboration between Auckland University's Liggins Institute and the Crown Research Institute AgResearch.

The study was led by Southampton University researchers.