The study of more than 500,000 kids in over 50 countries links fast food to severe asthma, hay fever and eczema.
Published in the journal Thorax, the study said kids who eat fast food three times or more a week had approximately 30% increased risk in disease severity. It's important to note, the study does not say fast food causes the conditions, instead it makes them worse.
On the flip side, researchers found a reduction in severity for kids who ate fruit at least three times a week. Doctors say that's because fruit and vegetables are full of anti-oxidants.
They also say when kids fill up with fast food, they don't eat as much of the fruit and veggies which could be making them feel better.