This was a very large study (the ISAAC research
project involves nearly 2 million children from more
than 100 countries worldwide) and, according to the
authors, is the first study to look at the association
between food types and the prevalence of asthma,
eczema and rhinitis on such a large scale. However,
while cross-sectional studies are very useful for determining
prevalence and possible associations, this study
design has some limitations. In particular, it cannot be
used to determine cause and effect. Not all confounding
variables could be adjusted for and it may be that
there are other factors that could explain any association
between ‘fast food’ intake and allergy symptoms,
such as SES. The authors highlighted the fact that they
were only able to adjust for SES at the country level
and it is possible that there may be an association at
the individual level.