Bad news, everyone. A new study has once again confirmed that fast food is bad for you. This time fast food has been linked to childhood asthma.

Using data from 500,000 kids in over 50 countries, the University of Auckland concluded that young children who eat fast food three or more times a week have a 27% greater risk of developing severe asthma.

Why is this? There are a couple theories on what might be happening.

1. Perhaps It’s Due to Trans Fatty Acids

Asthma generally occurs because the immune system is overacting to certain environmental stimuli. Trans fatty acids have been shown to affect immune system reactions. And fast food is chock full of trans fatty acids. It’s possible that through some mechanism we don’t yet understand, excessive trans fatty acids cause the immune system to overact, leading to asthma.

2. Perhaps the Study Found a Correlation, Not a Causation

According to Dr. Stephen Teach, “It would be wrong to assume from the results of this study that fast foods directly cause allergic disease.” For example, children who eat a lot of fast food may have a lower socioeconomic status. If they live in a poorer area with more air pollution, that could be what’s actually causing the asthma.

Whatever the case, there is some good news. The study also showed that children who eat three or more servings of fruit a week had a lower than average risk of developing asthma.

So at the end of the day, the lesson is one you probably already knew, but an important one nonetheless—Don’t eat too much fast food, and remember your fruits and veggies.