Addressing the limitations of the study, Keith-Thomas Ayoob, of Albert Einstein College of Medicine in New York City, pointed out that there was no information on dietary supplements or consumption of certain food groups, such as dairy.
"It's very possible that kids whose diets lack adequate fruits and vegetables and fish are also lacking in certain nutrients, that they are overweight, that their diets lack calcium, and on and on," Ayoob said in an e-mail.
"There are missing pieces here," he continued, "so I would advise parents to make it a priority of ensuring that children get enough fruits, vegetables, and low-fat dairy foods on a daily basis, whether or not their kids have asthma."
The study was also limited by the retrospective collection of dietary information, which is subject to recall bias, and by the inability to adjust for total energy intake and body mass index, according to Nagel and her colleagues.
They and several physicians contacted about the study also noted that numerous comparisons were performed, apparently without statistical adjustment.
This "raises the likelihood of 'fluke' associations," according to Dr. David Katz, director of Yale's Prevention Research Center. "This is partly, but not entirely, mitigated by the findings being in accord with a priori hypotheses (i.e., the researchers finding what they were looking for)."