Researchers in Spain discovered that the eating habits of expectant mothers and their offspring affected childhood wheeze and allergic reaction.
Children who consumed more than 60g (2.12oz) of fish and and 40g (1.41oz) of "fruity" vegetables a day, such as tomatoes and aubergines, were found to be less likely to suffer from asthma and allergies.
The study, which is included in the latest edition of the journal Pediatric Allergy and Immunology, charted the progress of 232 boys and 228 girls from the womb to age six and a half.
Researchers found that just under 9% of the children suffered from some degree of wheezing, including around 6% with allergy-related asthma.
In addition, 17% reacted to at least one of the allergens in a skin prick test.
However, those with a diet high in fish and "fruity" vegetables were less prone to suffer, the study found.
Author of the report, Dr Leda Chatzi, from the Department of Social Medicine at the University of Crete, said, "After adjusting the results for a wide range of variables, we concluded that the link between symptom-free children and a diet rich in fruity vegetables and fish was statistically significant.
"The biological mechanisms that underlie the protective effect of these foods is not fully understood, but we believe that the fruity vegetables and fish reduce the inflammation associated with asthma and allergies."
Professor John Warner, head of the department of paediatrics at Imperial College London, said, "The interesting thing about this study is that it followed a large number of children from the womb to the age of six and a half and incorporated a wide range of dietary, social and health factors.
"It provides parents with specific advice about the health promotion benefits of including fish and fruity vegetables as part of a balanced diet for both their children and the rest of the family."
From the September 24, 2007, Prepared Foods e-Flash