Bread and cereal could be helping to make western children short-sighted. Diets high in refined starches, such as breads and cereals, increase insulin levels which affect the development of the eyeball, say scientists.

The eyeball becomes abnormally long, leading to short-sightedness due to the lens failing to focus a sharp image on the retina, suggests a team of US and Australian experts.

The theory could help to explain the big increase in myopia in developed countries over the past 200 years, New Scientist magazine reported yesterday.

Short-sightedness affects 30% of people of European descent.

Jennie Brand Miller, a nutrition scientist at the University of Sydney, said modern processed breads and cereals made the rate of starch digestion faster. In response, the pancreas pumped out more insulin.

Fellow expert Bill Stell, from the University of Calgary in Canada, said the idea was plausible.

"It wouldn't surprise me at all," he said. "Those of us who work with local growth factors [proteins that promote growth] within the eye would have no problem with that - in fact we would expect it."

Evidence of the trend may be seen in Inuit and Pacific islanders. While less than 1% of these people had myopia in the past century, their rates have since rocketed, in some cases to 50%.

This has been blamed on the increase in reading following the sudden advent of literacy and compulsory schooling in such societies. But reading does not explain why the incidence of myopia has remained low in communities that have adopted western lifestyles but not western diets, say the scientists.

Loren Cordain, one of the researchers from Colorado State University at Fort Collins, said: "In the islands of Vanuatu they have eight hours of compulsory schooling a day, yet the rate of myopia in these children is only 2%."

She said the reason was probably that the Vanuatuans eat fish, yam and coconut rather than white bread and cereals.

The theory is also consistent with observations that people are more likely to develop myopia if they are overweight or have adult-onset diabetes. Both conditions involve elevated insulin levels.

The progression of myopia has also been shown to be slower in children whose protein consumption is increased.