Developed countries have experienced an increase in the symptom prevalence of non-communicable diseases (NCDs) of asthma, rhinitis and eczema in the past few decades^1,2 and as developing countries become more urbanised these diseases appear to be increasing^3-5. The incidence of many other NCDs has been linked to diet and many developing countries are moving away from the traditional diet of locally grown foods as they become more westernised⁶. Migration and food aid (with increased consumption of processed foods) as well as the increased consumption of fast foods^7,8, have been associated with the rapid increase in asthma prevalence, suggesting these may bring potent modifiable environmental factors⁹.

The International Study of Asthma and Allergies in Childhood (ISAAC)

ISAAC is a multi-centre, multi-country, multi-phase crosssectional study. ISAAC Phase Three involved 13-14 year old adolescents and 6-7 year old children. Schools were chosen randomly from a defi ned geographical area¹⁰. Standardised core written questionnaires and an optional environmental questionnaire (EQ) [www.isaac.auckland.ac.nz] were used to test specifi c etiologic hypotheses. Questionnaires on the symptom prevalence of asthma, rhinoconjunctivitis and eczema and types and frequency of food intake over the past 12 months were completed by the adolescents, and by parents/guardians of the children. Prevalence odds ratios (ORs) were estimated using logistic regression, using a random (mixed) effects model. Further multiple regression analyses were conducted to investigate whether associations between symptoms and diet were confounded by other risk factors for which information was collected in the EQ, and which had shown associations with symptoms in the univariate analyses. These were exercise, television watching, maternal education, maternal smoking in the first year of life (children only), and current maternal smoking. Data from 319,196 adolescents from 107 centres in 51 countries, and 181,631 children from 64 centres in 31 countries were included in the analysis.

Protective foods

• Adolescents
  For all centres combined, fruit intake once or twice per week and ≥ 3 times per week was inversely associated for current wheeze and severe asthma, as well as current and severe rhinoconjunctivitis and severe eczema once or twice per week. Milk was inversely associated with current wheeze once or twice per week, severe asthma ≥ 3 times per week, current and severe rhinoconjunctivitis once or twice per week and current and severe eczema once or twice per week as well as ≥ 3 times per week for current eczema. Vegetable consumption was also inversely associated with current wheeze ≥3 times per week.
• Children
  For all centres combined, eggs, fruit, meat and milk were inversely associated ≥3 times per week with all three conditions, current and severe. Cereal ≥3 times per week was inversely associated with severe asthma. Vegetables once or twice per week and ≥3 times per week were inversely associated with current and severe wheeze as well as for current and severe rhinoconjunctivitis and ≥3 times per week with current eczema.

Risk factor foods

• Adolescents
  For all centres combined, fast food once or twice per week and ≥3 times per week was positively associated with current wheeze, and severe asthma, ≥3 times per week with current rhinoconjunctivitis severe rhinoconjunctivitis and severe eczema.
• Children
  For all centres combined, fast food once or twice per week and ≥3 times per week was positively associated with current wheeze and and severe asthma. Fast food consumed ≥3 times per week was positively associated with current and severe rhinoconjunctivitis and severe eczema.

Conclusion

Our results suggest that the consumption of fast food may be contributing to the increasing prevalence of asthma, rhinoconjunctivitis and eczema in adolescents and children. Fruit showed a slightly smaller but protective effect for the three conditions. For other foods, the picture was less clear. However, in concordance with international dietary recommendations, diets that have a regular consumption of fruit and vegetables are likely to protect against asthma, allergic disease and other non-communicable diseases.