Heavy Math

Health Officials Hope to Make Fat Calculations Standard Practice

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Public Health Feature -- August 2003

By  Ken Ortolon
Senior Editor

It was not his intention when he opened his pediatric endocrinology practice in Corpus Christi, but Stephen Ponder, MD, CDE, says he has become Corpus Christi's "fat doctor."

Dr. Ponder says 40 percent of the children he sees in his practice are overweight or obese, many of them referred to him by the public schools through the South Texas acanthosis nigricans (AN) screening program. AN is a marker for insulin resistance and increased risk for developing type 2 diabetes.

"We get a lot of kids coming in who weigh 300 or 400 pounds when they're in their early teen years," he said. "When I see these 15-year-old morbidly overweight kids, we backtrack on their growth charts and see that they were well above the growth curve by age 3."

Obesity is a full-fledged epidemic. The Texas Department of Health (TDH) says 36.7 percent of adult Texans were overweight and 24.6 percent were obese in 2001, up from about 30 percent and 12 percent, respectively, since 1990. Among children, the prevalence of obesity ranged from 29.4 percent for 11th graders to 38.7 percent for fourth graders.

Public health officials urge physicians to fight this epidemic by focusing more attention on weight as part of routine office visits. The first step in doing that, they say, is to make calculating a patient's body mass index (BMI) as standard as taking the patient's temperature during every office visit. (See "TMA Fights Fat.")

Doing the Math

"It was about 20 years ago that everybody was beginning to learn their cholesterol number or their blood pressure, and understand what the values meant and that those values could put them at risk for chronic disease," said Barbara Keir, director of the TDH Division of Public Health Nutrition and Education. "We're trying to do the same thing with BMI. Unfortunately, not many doctors use the BMI today."

The BMI indicates weight status. According to the U.S. Centers for Disease Control and Prevention (CDC), it is one of several factors physicians can use to predict risk of diseases such as cardiovascular disease, high blood pressure, and diabetes.

For adults over age 20, the calculation is relatively straightforward. First, square the patient's height in inches. Then divide his or her weight in pounds by that number and multiply the resulting number by 703.

For example, for a patient who is 5 feet 10 inches tall and weighs 200 pounds, you would square 70, which equals 4,900. Then divide 200 by 4,900, which equals 0.004. Then multiply by 703 to get the BMI, which is 28.69.

A BMI between 18.5 and 24.9 is considered normal. Below 18.5 is underweight. Between 25 and 29.9 is overweight, and 30 or above is obese.

For children, the calculations are a little more complicated. Children's body fatness changes over the years as they grow. Also, girls and boys differ in their body fatness as they mature.

Because of these factors, the BMI calculation for children must be age and gender specific and must be plotted on gender-specific growth charts to determine where a child's weight falls in relation to the weight of other children that age.

Children whose BMI falls below the 5th percentile are underweight. Those with a BMI between the 85th and 95th percentile are at risk of being overweight. And kids whose BMI is above 95 percent are overweight.

On Your Desktop

While physicians and nurses dealing with adults likely would have time to do the quick BMI calculations during a routine office visit, a pediatrician or family practice doctor might find it daunting to plot a child's BMI percentile during a 10-minute office visit and still take care of the child's earache or injury.

"If a physician is working with parents trying to track their children's weight, trying to sit there and calculate the body mass index and then plot it on the percentile chart is ridiculous. You don't have time," said Joan Carter Clark, a registered dietitian and instructor of pediatrics at the Children's Nutrition Research Center at Baylor College of Medicine in Houston. "It's a time-crunch situation, but we have an obesity problem in this country, and prevention is a whole lot better than intervention."

To encourage both physicians and parents to pay more attention to weight, the research center has developed an interactive tool that physicians, nurses, and parents can use to quickly determine a child's BMI percentile. The Children's BMI & Percentile Graph Calculator, which can be found under "Nutrition News & Tools" on the Baylor Web site at www.bcm.tmc.edu/cnrc, automatically calculates a child's BMI and plots the percentile on the CDC growth chart.

"The tool provides a snapshot," Ms. Clark said, "but the value of the snapshot is that when you put a bunch of snapshots together you have a movie. And that's what this will give you if you use it on a regular basis. It will give you a view of where the child's been and a good idea of where he or she is going if nothing changes."

If a child is at the 60th percentile at one office visit but begins moving to higher and higher percentiles at subsequent visits, then the physician knows the child's weight has gone off track and intervention is needed, Ms. Clark says.

"You're trying to catch children when prevention is the easiest thing for the entire family to do, to intervene early," she added. "With this BMI percentile look, a nurse or doctor can quickly enter in the numbers, the percentile is calculated for you, and you can quickly plot that number in the growth chart and keep it in the child's file or send it home with the parents. It gives you something to monitor."

In addition to the Baylor BMI calculator, CDC has a considerable amount of information on body mass index, including formulas for BMI and BMI calculators for both children and adults, on its Web site at www.cdc.gov.

Beyond the Calculations

While the BMI is a useful tool, it has its limitations. The BMI for children does not apply to children under age 2, and extremely athletic and heavily muscled teens and adults will have an elevated body mass index that might incorrectly place them in the overweight or obese category.

"Barry Sanders had a BMI of 31, which is not even overweight, it's obese," Dr. Ponder said. "Michael Jordan had one of 25, which is right on the borderline of being overweight. So there are a lot of people that would be considered overweight by BMI standards who are otherwise well-conditioned athletes."

Still, Dr. Ponder routinely calculates BMI for his pediatric patients and uses a body fat analyzer to determine percentage of body fat, as well. But just plotting a child's BMI on the growth chart is not enough, he says. Physicians need tools to help them counsel patients about weight, nutrition, and exercise, he says.

"The BMI is probably your ticket in the door, but you've got to have something to offer them once you get them through that door," Dr. Ponder said. "Nobody gave me any training about that in med school. While there may be more schools starting to discuss it, we have a long way to go in terms of how do you counsel families about nutrition when you have 10 minutes or less to spend with them and you have 30 kids waiting out in the waiting room."

Dr. Ponder has developed a "five-minute consult" that he uses with his patients. It focuses on four key points:

  • Reducing consumption of soft drinks, sports drinks, and other high-calorie beverages;
  • Cutting out fast food or at least avoiding the "super size" portions;
  • Reducing snacking between meals; and
  • Increasing physical activity.

"I can usually go over those things in five minutes with the family," Dr. Ponder said. "If you're a pediatrician, that's the message you want to get out to people."

Both Dr. Ponder and Ms. Clark say it is critical that physicians begin to intervene early so that eating and exercise habits can be changed before a child becomes obese.

"The people on the front lines don't include me, the pediatric endocrinologist. The family doctors, the pediatricians, and the generalists are seeing these kiddos," Dr. Ponder said. "They certainly do play a role because they see them so early in life. They ought to be intervening earlier, before the children end up coming to see me at 12 and 13 and weighing 300 and 400 pounds. By then, their habits are set, the weight gain is dramatic, and they have so many complications of their weight."

Ken Ortolon can be reached at (880) 880-1300, ext. 1392, or (512) 370-1392; or by email at Ken Ortolon.

SIDEBAR

TMA Fights Fat

The Texas Medical Association offers physicians some ammunition in the ongoing battle to reduce Texans -- not their number, just their size.

The TMA Web site at www.texmed.org has an easy-to-use body mass index (BMI) calculator you can use to determine your own BMI or that of a patient. Just click on the appropriate weight on the scale shown in the picture, then click on the appropriate height. A flashing, multicolor bar graph then appears, showing the BMI.

The BMI page also has a link to the pediatric BMI calculator at Baylor College of Medicine.

The TMA Web site also has a lengthy report on the childhood obesity epidemic  (PDF) and what you can do about it, as well as U.S. Department of Agriculture dietary guidelines.

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