The researchers found that, out of the 15 food types in the questionnaire, only fast food showed an association with asthma and eczema in both age groups regardless of gender and socio-economic status. Three or more servings a week was linked to a 39 percent increase in severe asthma among teens and a 27 percent increased risk among younger children.
"A consistent pattern for the adolescent group was found for the relationship between symptoms and fast foods," the researchers wrote in the study. "As adolescents are generally known to be high consumers of fast food, these results that show a significant increased risk of developing each or all three conditions may be a genuine finding."
Though both eczema and asthma can be triggered by food allergies—and typical fast-food meals are filled with common allergens like gluten, dairy, egg, and soy—Williams told Yahoo! Shine that allergies probably aren't the main issue here.
"We did not look for gluten, although bread and pasta both have gluten (however gluten free pasta and bread are now widely available so when someone says yes to eating bread 3x per week it may well be that they ate gluten free as this practice is growing in some countries). So we cannot tease this out," he wrote in an email. "There is no doubt that food allergy plays an important role in some people with severe asthma and eczema, but those people tend to recognize it and avoid those foods."
"I doubt if our observation of an association between severe allergies and fast foods is mediated much by increased food allergens," he added.
A 2011 study published in Nutrition Research and Practice suggested that additives in processed foods could also trigger an allergic reaction in some kids, but Williams and his team say that fat intake, not food allergies or additives, is probably the main culprit.
Image: French fries, via Shutterstock