Have you been wondering why your 12-year-old daughter is gaining so much weight? Have you been concerned that your 15-year-old looks too thin?

To find out about teenage girls and body image, we interviewed Martin Fisher, M.D., chief, Division of Adolescent Medicine, North Shore University Hospital in Manhasset, New York. Dr. Fisher shared his views, based on 20 years of experience in adolescent medicine.

According to Dr. Fisher, girls experience their major height spurt early in puberty (the time of hormonal changes which bring about physical changes,) about six months to a year before their first period. (It's interesting to note that in the 1850s, the average age for a first period was 16; the average age dropped a year every generation until it stopped at 12 1/2.) Once they get their period, girls will grow 2.5 to 7.5cm (about one to three inches) over the following one to three years. But the growth spurt isn't just in height, it's in weight, too. The average young adult female at 1.5m (4'11") tall weighs 45kg. (99 lbs) While the average 10-year-old weighs about 36kg, (79 lbs.) a 16-year-old may weigh 55kg, (121 lbs.) which means a weight gain of 19kg. (42 lbs.) in just a few years. Around the time of puberty, (usually 11 to 13 for girls) the physical, hormonal and emotional changes, combined with the rising importance of the peer group, come together to create a certain intensity around body image in girls.

LITTLE GIRLS ON A DIET

There is an ever-increasing concern among girls and women about being thin. Surveys in the US now show that a fair percentage of girls in third to sixth grade are worried about their weight and are inappropriately on some type of diet.

This over-concern with body image, coupled with and fed by the fashion and entertainment industry's emphasis on thin women, has led to an increase in eating disorders in teenage girls that has been building since the 1960s.

The two major eating disorders are anorexia nervosa, in which a girl will so severely limit her food intake that she becomes extremely thin; and bulimia, in which people binge (overeat) -- and then purge (vomit) usually secretly. In the US and England, anorexia nervosa is said to afflict 0.5 percent of high-school and college girls (that is, one in 200) and bulimia, one to five percent of the same age group.

A girl suffering from anorexia nervosa is tremendously worried about gaining weight but won't necessarily admit it. When taken to a doctor by worried parents, she will often say she knows she is too thin and needs to gain weight.

Dr. Fisher sees the phenomenon as a pyramid, with the bottom layer representing the desire to lose weight, which applies to many adolescent girls. Of those, a certain number will begin a diet. Of those, fewer will complete the diet. Of those, even fewer will over-diet and of those, fewer will develop signs of an early eating disorder.

DANGER SIGNS

Dr. Fisher says that this is the time for parents to take action because if the disorder is not caught at this stage, it may escalate into a full eating disorder which can be dangerous and even fatal. (Five to 10 percent of girls hospitalized for an eating disorder die. The majority of them are suicides.) If a girl is on a diet and begins to miss her period, her parents should take her to a doctor.

Experts are still studying eating disorders, but the feeling is that girls with a psychological vulnerability and/or low self-esteem are the ones affected. Families of girls with eating disorder often display more addictive, obsessive or compulsive disorders.

Sometimes the girls are encouraged by the positive feedback they get when they first lose weight. Some girls have said to Fisher and his colleagues, "This was the one thing I could do better than my friends. Everybody talks about it, but I did it."

Fisher's advice to parents: Accept the fact that much concern with weight and appearance is perfectly normal, but keep your eyes open for a crossing of the line (a major preoccupation with weight; a major change in eating habits; excessive exercise or use of diet pills; signs of vomiting).

Acting early is always better than acting late, even though the girl may get angry. If caught early, the prognosis is much better. Once an eating disorder becomes entrenched, it is harder to eradicate.