2022年考博英语阅读篇章材料(28)

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　　Blinded by Bread

　　Don't hold the book too close to your eyes or you'll need glasses, parents

　　often warn their children. But the food kids eat might play just as big a role

　　as books and computer screens when it comes to? shortsightedness.

　　Diets high in refined starches such as breads and cereals in- creased

　　insulin levels. This affects the development of the eyeball, making it

　　abnormally long and causing shortsightedness, suggests a team led by Loren

　　Cordain, an evolutionary biologist at Colorado State University in Fort Collins,

　　and Jennie Brand Miller, a nutrition scientist at the University of Sydney. The

　　theory could help explain the dramatic increase in myopia in de- veloped

　　countries over the past 200 years, it now affects 30 per cent of people of

　　European descent, for example.

　　“The rate of starch digestion is faster with modem processed breads and

　　cereals,” says Brand Miller. In response to this rapid digestion, the pancreas

　　pumps out more insulin. High insulin is known to lead to a fall in levels of

　　insulin-like binding protein-3, the team points out. That could disturb the

　　delicate choreography that normally coordinates eyeball lengthening and lens

　　growth. And if the eyeball grows too long, the lens can no longer flatten itself

　　enough to focus a sharp image on the retina, they suggest.

　　“It’s a very surprising idea,” says James Mertz, a biochemist at the New

　　England College of Optometry in Boston. But it's plausible, says Bill Stell of

　　the University of Calgary in Canada. “It wouldn't surprise me at all. Those of

　　us who work with local growth factors? within the eye would have no problems

　　with that—in fact we would expect it.”

　　Mertz’s institution is now planning studies in animals. But there is

　　already evidence to support the theory. While fewer than 1 per cent of the Inuit

　　and Pacific islanders had myopia early in the last century, these rates have

　　since skyrocketed to as high as 50 per cent. These “overnight epidemics?” have

　　usually been blamed on the increase in reading following the sudden advent of

　　literacy and compulsory schooling[2] in these societies.

　　But while reading may play a role, it doesn't explain why the incidence of

　　myopia has remained low in societies that have adopted Western lifestyles but

　　not Western diets, says Cordain. “In the islands of Vanuatu [3] they have eight

　　hours of compulsory schooling a day,” he says, “yet the rate of myopia in these

　　children is only 2 per cent.” The difference is that 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 of

　　which involve elevated insulin levels. The progression of myopia has also been

　　shown to be slo- wer in children whose protein consumption is increased.

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