Children who eat a Mediterranean diet rich in fruit, vegetables and fish have a lower risk of asthma and wheezing, experts said today.
But eating three or more burgers a week can increase the risk, although this may be linked to other unhealthy habits, they said.
Researchers from Germany, Spain and Britain examined data from 50,000 children aged eight to 12, collected between 1995 and 2005. The youngsters were from 20 countries around the world, including affluent and poorer nations.
Parents were asked about their children's usual diet and whether they had ever been diagnosed with asthma or if they had suffered wheezing.
Almost 30,000 children were tested for allergic reactions using a skin prick test to see if diet directly affected their chance of developing common allergies.
The experts found diet did not increase the risk of allergies to grass and tree pollen but did have an effect on asthma and wheeze. Children who ate a diet rich in fruit had a low rate of wheeze in both rich and poor countries, the study found.
Meanwhile, a diet high in fish protected children against wheeze in rich countries, while a diet rich in cooked vegetables protected children in poor countries.
The authors, writing in the journal Thorax, said: "Fruit and vegetables contain antioxidants and other biologically active factors which may contribute to the favourable effect of fruit consumption in asthma.
"In particular, foods rich in vitamin C have been reported to relate to better lung function and fewer asthma symptoms."
They said carotenoids -- contained in fruit and vegetables such as sweet potatoes and carrots -- and vitamins C and E also have a positive effect on lung function.