The findings come from a study of some 2,100 teens in 12 U.S. and Canadian communities.
In a nutshell, the teens with less than ideal diets were the most likely to have poorer lung function -- including asthma symptoms -- than their peers.
On the flip side, those eating plenty of fruits, vegetables, and omega-3 fatty acids (found in salmon and other fatty fish, walnuts, flaxseeds, and other foods) tended to have better lung function.
The researchers included Jane Burns, ScD, of the Harvard School of Public Health.
"I wish I could say that an apple a day can keep asthma away, but it's a complex disease with a genetic component," Burns says in a news release.
"However," she says, "it may be that certain foods can lessen or prevent asthma symptoms. The most important thing to remember is that diet can have a significant impact on teens' respiratory health. I would encourage them to make healthy eating a part of their routine, and stress to them that smoking is bad."
The study appears in July's edition of the journal Chest.
Asthma and Diet in Teens
Teens with good diets were few and far between. For instance, 86% of the teens admitted not eating at least five daily servings of fruits and vegetables.
Thirty percent of the students were overweight, 9% had asthma, 24% were smokers, and 11% took multivitamins.
Students who skimped on fruits, vitamins C and E, and omega-3 fatty acids were particularly likely to have poorer lung function and asthma symptoms, especially if they were smokers.
The study doesn't show which came first -- poor diets or poor lung function. It also doesn't rule out other influences, such as the teens' social and economic backgrounds, or their eating habits as children.