To lose weight or wait it out?

Who should lose weight, and who should "grow into" his or her weight"? A 13 year old girl who weighs 200 pounds will not grow into her weight because that weight is too high to be healthy unless she reaches 6' tall. Recommendations from a committee of experts, published in the medical journal Pediatrics, and currently under review, state that weight loss is recommended for overweight teens who have:

• a BMI in the 95th percentile or higher.
• a BMI from the 85th up to the 95th percentile if they have medical problems, such as high blood pressure, related to their weight.

However, for teens whose weight problems are less serious - that is, those with a BMI placing them from the 85th up to the 95th percentile and without weight-related medical problems - maintenance is recommended, because they can grow into their weight through physical activity and healthy eating. For young people in this category who are finished growing, gradual weight loss would be appropriate, according to Sarah Barlow, MD, a member of the committee.

What's a safe rate of slimming down for overweight teens who meet the criteria for a weight loss? Dr Barlow says, "I'm comfortable with a teen losing at a rate of one to two pounds per week. Losing faster than that may mean that the body will start losing too much muscle tissue along with the fat, and that's not healthy. If a teen's hungry all the time, that's another sign that a diet is too strict and weight loss is too fast."

The best way to find out whether an overweight teen should be losing weight or "waiting it out," according to the guidelines, is to check with a physician.

BMI Basics

As of this writing, most health care professionals in the US use the following indicators to define weight problems in teens.

Overweight: The BMI for a teen's age and gender is greater than or equal to the 95th percentile. For instance, a sixteen year old girl who is 5'3" and weighs 175 pounds would be in the 97th percentile; a sixteen year old boy who is 5'8" and weighs 195 pounds would be in the 97th percentile. Nearly 9 out of 10 of the teens interviewed fell into this category at their highest weight; 60 were in or above the 99th percentile before losing weight.

At risk for overweight: The BMI for a teen's age and gender is anywhere from the 85th percentile upto but not including the 95th percentile. For instance, a 16 year old girl who is 5'3" and weighs 150 pounds would be in the 91st percentile; a sixteen year old boy who is 5'8" and weighs 169 pounds would be in the 91st percentile. Just 7 of the teens interviewed fell into this category at their highest weight; none were below this category.

(BMI percentiles were not available for a small number of the teens at their highest weight.)

How much weight is too much?

From a health standpoint, what's a healthy weight, and at what weight is a person at risk for developing health problems? Several studies suggest that many teens don't know when they've reached an unhealthy weight - and neither do their parents. In fact, the considerations are different for adults and teens. For adults, the gold standard for defining healthy weight is something called body mass index, or BMI, a number that measures weight in relation to height. When an adult's BMI is 25-plus, health risks increase compared with someone who has a BMI of less than 25; 25 to 29.9 is considered overweight, and 30 or above is obese. (BMI is calculated by dividing weight in pounds by the square of height in inches, then multiplying that number by 703. BMI charts are available in books, at doctors' offices, and on many health-related Web sites.)

For children and teens, the picture is more complicated, because what's considered a healthy weight and normal amount of body fat changes with age and differs in boys and girls. The best way to determine a teen's weight status is to consult a physician and to use special pediatric growth charts developed by the Centers for Disease Control and Prevention for children ages two through nineteen. These charts plot weight according to percentiles for kids of the same age, gender, and height. (The Centers for Disease Control and Prevention provides an interactive computerzied BMI calculator that does the work for you. Visit this Web site: http://apps.nccd.cdc.gov/dnpabmi/calculator.aspx.)

BMI and the BMI growth charts are only rough guides for a healthy weight. For instance, some teens fall into the "at risk" category for being overweight becuase they're muscular, not because they hae excessive body fat levels.

It's also important not to go by any single measure of BMI percentile for a child or teen. Rather, BMI percentile should be watched over time to see if a child is staying on track. According to Roman Shypailo, a body composition expert at the Baylor College of Medicine, "The important thing is to watch for significant 'drifting' in a teen's BMI percentile, either up or down." In other words, if there's a sudden large increase or if a teen creeps up by three or four units every year, that's probably cause for concern. But if he or she has been on the same track for years - even if it's somewhat on the high side - there's less reason to worry.

Although it's unwise for kids and their parents to be obsessively calculating BMI and BMI percentile, it's probably a good idea to calculate them periodically, with a physician's help.