Doctors could do more to help at-risk teenagers who are trying to lose weight by vomiting, taking diet pills and skipping meals, a study has found.
Drawing on a survey of about 9000 New Zealand high school students, University of Auckland researchers identified healthy and unhealthy weight-loss strategies used by teenagers.
They noted that fasting and skipping meals were more common "red flag" behaviours, which were associated with poorer well-being and mental health.
The study found that clinicians rarely asked young people how they tried to control their weight.
"This may be due to uncertainty about which questions to ask, specifically around whether certain weight-loss strategies are healthier or unhealthy or about what weight-loss behaviours are more likely to lead to adverse outcomes," its report said.
"Routine assessment of weight-control strategies by clinicians are warranted, particularly for meal skipping and fasting for weight loss."
The study, in the International Journal of Behavioural Nutrition and Physical Activity, cited a 2009 Youth Risk Behaviour survey, which suggested that more than 4 per cent of adolescents vomited for weight loss in the 30 days before the survey, 5 per cent took diet pills, and 10 per cent went without eating.
"Unfortunately, unhealthy weight-control behaviours are common, especially among overweight young people, and there is abundant evidence that unhealthy weight-loss behaviours lead to poor outcomes for adolescents," the study said.
"For example, adolescents who used diet pills, vomited, took laxatives, took diuretics, fasted, used food substitutes, skipped meals or smoked cigarettes for weight loss had high levels of depression and were more likely to develop suicidal behaviours into young adulthood."
Adolescents who used these extreme weight-control methods ate fewer fruits and vegetables and more high-fat foods than those who were not dieting or using only moderate weight-control strategies.
"Furthermore, skipping meals is not an effective weight-loss strategy, as available research on successful weight loss suggests that regular meal consumption, particularly breakfast, is important in weight maintenance," the researchers said.
Students who made weight-loss attempts were more likely to be female (67 per cent) than male, but there were no differences by age.
The study used data collected as part of Youth '07, a national survey of secondary school students aged around 13 to 18.
* Exercise often - try 60 minutes of physical activity a day.
* Eat lots of fruit and vegetables, cereals, low-fat dairy products, lean meat, chicken or fish.
* Cut down on fatty foods.
* Reduce sugar and salt.
* Talk to a doctor or nurse before dieting.
* Use diet pills, diuretics or laxatives.
* Skip meals and fast.
* Force yourself to vomit after meals.