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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, a team of international scientists has claimed.

Researchers from the UK, New Zealand and Singapore, said the study, to be published next week, provided the first scientific evidence linking pregnant women's diet to childhood obesity.

"We have shown for the first time that susceptibility to obesity cannot simply be attributed to the combination of our genes and our lifestyle, but can be triggered by influences on a baby's development in the womb, including what the mother ate," said Southampton University's Professor Keith Godfrey, who led the research.

The study, which will be published in the journal Diabetes, showed that what a mother ate during pregnancy could change the function of her child's DNA through a process called epigenetic change.

Researchers measured epigenetic changes in nearly 300 children at birth and showed that these strongly predicted the degree of obesity at six or nine years of age.

Children with a high degree of epigenetic change were more likely to develop a metabolism that "lays down more fat," regardless of the mother's weight and how much her child weighs at birth, researchers found.

Professor Peter Gluckman, from Auckland University's Liggins Institute, said the rate of epigenetic change was possibly linked to a low carbohydrate diet in the first three months of pregnancy, but it was too early to draw a definitive conclusion and further studies were needed.

He said one theory was that an embryo fed a diet containing few carbohydrates -- which provide the body with energy -- 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.