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.
Data from more than 500,000 children in more than 50 countries suggests poor diet may be to blame for rising levels of these allergy-related conditions.
Those who ate fast food, such as take-away burgers, risked severe asthma, eczema and itchy, watery eyes.
Eating plenty of fruit appears to be protective, Thorax journal reports.
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%.