They constantly obsess about their weight and waistlines. A small indulgence, like a piece of chocolate, may cause them to spend hours in the gym burning off excess calories.
Some may try to purge whatever they have binged on by vomiting or taking laxatives, just so they can resemble the latest runway model or superstar.
Such behaviour of self-starvation or purging after an episode of binging is typical among women with eating disorders.
Today, however, what is often regarded as a women's disease is affecting adolescent boys, too.
According to Ms Vyda Chai, a clinical psychologist at Think Psychological Services, studies have shown that men, like women, are increasingly pressured to have the ideal body.
Ms Chai said almost 15 per cent of the cases she sees for eating disorders are teenage boys. The figure is startling given that, only five years ago, almost all her patients were female.
"In the world we live today, there is a greater emphasis on having an athletic physique which means keeping the body weight on the low end of the BMI (Body Mass Index). The drive for thinness and heightened media coverage reinforces this ideal body image," she said.
By and large, eating disorders among teenagers here are on the rise. At the Singapore General Hospital (SGH), the number of people seeking help for eating disorders has more than tripled from 35 to 126 cases annually since its eating disorders programme started in 2003.
Teenagers account for half of the 126 cases seen last year at SGH.
Dr Lee Huei Yen, director of the Eating Disorders Programme and senior consultant at the Department of Psychiatry, said approximately 10 per cent of the cases seen are males.
The figures may be an under-representation, especially since "males tend to have more avoidant personalities or hide their difficulties behind the gym" compared to women who tend to speak more openly about their insecurities, said Ms Chai.
Among her recent male patients, Ms Chai noted that many of them exhibited more passive aggressive and avoidant-type personality styles. Many also suffer from other psychiatric disorders such as depression and anxiety.
Dr Adrian Wang, consultant psychiatrist at Gleneagles Medical Centre, said men generally avoid seeking counselling help, especially since eating disorders are considered "a female-dominated illness".
While anorexia may be more easily detected - due to drastic weight loss and an emaciated appearance - bulimia and binge-eating may be harder to detect in males, added Dr Lee. A 2007 Harvard study on 3,000 men and women has shown that as many as 40 per cent of binge eaters were men.
"Males are generally known for having a hearty appetite, so most people would not think much of guys eating more," said Dr Lee.
While eating disorders can occur at any age, Ms Chai said that they tend to have their roots during the teenage years when peer relationships become more complex.
Parents have a role to play by showing "a lot of care and concern", said Dr Lee.
"My advice is to first seek help from somewhere less 'threatening' rather than go straight to a psychiatrist. For instance, attend a support group, see a general practitioner (GP) or go to the polyclinic," advised Dr Lee.
"If the family could just put it to them that they should go and see a GP for a medical check-up, it makes it less threatening for the person."
More often than not, treatment for eating disorders is a long drawn-out process that may take years.
Dr Lee noted that recovery is often quicker and easier for cases which are detected early. About 50 to 70 per cent of bulimics and a third of anorexics recover after five years treatment.
At SGH, which offers an outpatient, inpatient and day programme, a multidisciplinary approach of counselling, psychotherapy coupled with medical and nutritional assessments is used to treat eating disorders.