Doctors have been asked to be on the lookout for teenagers who may be chewing and spitting out food, a practice reported by at least one in 10 adolescents in a recent study.

It is the first time the prevalence of the eating disorder symptom has been identified among Australian adolescents, the researchers say.

In the online survey of more than 5000 students aged 11-19 from NSW schools, 12.2% said they had chewed their food and spat it out at least once a week over the previous 28 days.

Researchers also found 2.5% reported chewing and spitting out food at least between once and twice weekly and 2.1% reported doing so more than twice a week over the past 28 days.