Eating fast food three times a week may lead to asthma and eczema in children, say researchers who have looked at global disease and dietary patterns.
Fast food often contains high levels of saturated- and trans-fatty acids, which are known to affect immunity, while fruit is rich in antioxidants and other beneficial compounds, say the researchers.
In the study, children in their early teens who ate three or more weekly servings of fast food had a 39% increased risk of severe asthma.
Six- and seven-year-olds had a 27% increased risk.
Eating three or more portions of fruit a week cut the risk of severe asthma, eczema and rhinoconjunctivitis by between 11% and 14%.
The study authors, Prof Innes Asher, from the University of Auckland in New Zealand, and Prof Hywel Williams, from the University of Nottingham in the UK, said: "If the associations between fast foods and the symptom prevalence of asthma, rhinoconjunctivitis and eczema is causal, then the findings have major public health significance owing to the rising consumption of fast foods globally."