Previous studies have shown that children born to obese mothers are likely to be overweight, but the new findings are some of the first to look at what behaviors may be triggering unhealthy eating habits, the researchers said.

"It indicates there is a foetal programming for overeating," said Neil Stickland, a researcher at the Royal Veterinary College in London who worked on the study. "The foetuses are getting used to this junk food during gestation," he added. "It is not just genetics," he said. "We can show a direct link to what the mothers eat and how it affects the children."

In the study, published in the British Journal of Nutrition, researchers took two groups of pregnant rats and gave one a diet of junk food such as doughnuts, muffins and sweets and fed the other nutritional pellets.

Surprisingly, Stickland said, there was no effect on birth weight. But when the young rats were weaned the team found that the animals whose mothers ate junk food put on weight more quickly, had a taste for unhealthy food and gorged, he added.

Studying rats has implications for humans because the mechanisms controlling appetite are similar in many species, Stickland said.