Teenagers have a 39% increased risk of severe asthma if they eat more than three helpings of burgers, chips and pizza each week – while children have 27% increased risk, say researchers.
Children and teenagers consuming three or more portions of fast food have an increased risk of severe eczema and severe rhinitis – a condition characterised by a runny or blocked nose and itchy and watery eyes.
The findings, from the International Study Of Asthma And Allergies In Childhood and published in the respiratory journal Thorax, have prompted the authors to suggest a fast-food diet may be contributing to the rise in the conditions.
The researchers said if the link was proved to be causal it would have major implications on public health.
They examined data on 319,000 13 and 14-year-olds from 51 countries and 181,000 six and seven-year-olds from 31 countries.
The teenagers and parents of the younger children were questioned on symptoms of asthma, rhinoconjunctivitis and eczema and their weekly diet.
Researchers also found eating fruit could have a protective effect on the youngsters. Consuming three or more portions a week was linked to a reduction in symptom severity of 11%-14% among teenagers and children, respectively.
Malayka Rahman, of Asthma UK, said: "We advise people with asthma to eat a healthy, balanced diet, including five portions of fruit or vegetables every day, fish more than twice a week, and pulses more than once a week."