What's the Big Deal About BMI?

Childhood obesity is a national problem that is begging for our intervention. We know that currently 15+% of 6 - 19 year olds are at or above the 95% for BMI on a standard growth chart.

The body mass index or BMI is a calculation of the weight in kilograms to the square of height in meters. BMI is widely used to define overweight and obesity because it correlates well with more accurate measures of body fatness and is easily obtained from routinely measured height/weight/age data. However, it is not perfect, and clinical judgment must be used in applying these criteria to a specific patient. Obesity refers to excess adiposity (fat tissue), not excess weight. BMI data should not be interpreted without clinical information.

Having said that, the state of PA has mandated that our public schools begin to identify “at risk” children by calculating BMIs of students as a routine screening practice. There is a wide range of “normal” for the BMI, and school nurses are being trained to identify those students who MAY BE at risk. If your child has a BMI between the 85^th and 95^th percentile for age and sex, they are considered at risk of overweight, and a BMI at or above the 95^th percentile is considered overweight or obese. Similarly, children at the other end of the BMI chart are considered underweight if their BMI is at or below the 5^th percentile and are at risk for being underweight if they fall between the 5^th and 15^th percentile.

Since prevention is one of the hallmarks of pediatric practice, physicians are being encouraged to track BMI beginning at age 3 years, and promote healthier lifestyle habits at an early age. The BMI should never be interpreted without additional information, including lifestyle habits (dietary habits, exercise habits, sedentary activities) other existing medical conditions and growth trends over time.

If I see a patient who is in the 80% ile for BMI at age 9, but at age 4 they were in the 20^th percentile, and at age 5 they were in the 40^th percentile, and at age 7 they were in the 60^th percentile, that trend raises a red flag for me, even though technically the BMI is in a “normal” range. It should prompt parents and health care providers to ask more questions. These questions should be: what does this child’s diet look like, what kind of activity is he getting on a regular basis, how much “screen time” (TV, computer and video games) and is there something else concerning going on here?

Similarly, a strong, muscular, athletic child who has always been at the 87^th percentile for BMI since age 4, but is very physically active, eats a wide variety of healthy fruits and vegetables, has minimal screen time and has a normal physical exam including blood pressure, is not “worrisome” to me from a health standpoint. I would counsel that patient and family that they must simply keep up the healthy lifestyle choices, or their BMI might put them at risk if they begin making less healthy choices.

So what’s a parent to do who is worried about their child’s BMI?

• Focus on health habits, and don’t use body shape/size or the word “fat” to discuss these concerns.
• Be a good role model for your children. Model healthy food choices, and routine physical activity. Children live what they see, not what they are told.
• Encourage healthy eating patterns by offering nutritious snacks, such as vegetables, fruits, low-fat dairy foods and whole grains. Encourage children’s AUTONOMY in self-regulation of food intake. Teach children early to “listen to their bodies” and eat when they are hungry and stop when they are full. Food should be for providing nutrition to their growing bodies, not used as a reward for good behavior. Celebrate by doing a family activity together (ice skating, biking, snowball fight, swimming), NOT by having ice cream sundaes!
• Limit screen time to a MAXIMUM of two hours per day. This includes TV viewing, computer time and video game time combined. Do NOT put a TV in the bedroom. There is a strong correlation between TVs in bedrooms and obesity.
• Set a house rule that all eating happens in the kitchen or dining room. “Mindless” eating in front of the TV or computer has shown to contribute significantly to the total number of calories consumed in a day. If you are hungry, give your body the attention it deserves by paying attention to what you are eating while you do it. In addition, eat SLOWLY. It takes about 20 minutes for the signal to get from your stomach to your brain to tell you that you feel full.
• Set a house rule that no foods should be eaten directly out of the container. Start early teaching your children what constitutes a reasonable portion size. Studies have shown that on average, a person eats FOUR TIMES the amount of potato chips if they eat them directly out of the bag instead of putting a portion size on a plate. If you aren’t sure how to make the portion sizes reasonable, buy individual portion bags.
• Eat out thoughtfully. Foods prepared in restaurants tend to be higher in fat, salt and calories than you would ordinarily prepare at home. Limit the number of times you eat out during the week, and when possible pick a restaurant that offers reasonably healthy alternatives. If you know you will be headed to a fast food restaurant to get a quick dinner, plan ahead. Resist the temptation to SUPER size and plan relatively healthy choices (hamburger with milk or water instead of soda, and split the fries among a few family members.)
• Make physical activity a regular part of your family’s day. Rake leaves together, shovel snow, go on walks around the lake, take a bike ride, or shoot hoops in the driveway. When you go shopping, park at the farthest spot away from the store instead of driving around the parking lot looking for the closest space. Take the stairs instead of the elevator.

Remember, this is not about making your children thinner. This is about creating a lifetime of healthy eating and exercise habits, so they can become healthy adults. Remember, a 4 year old who is obese has a 20% chance of becoming an obese adult with all the associated health problems. A 14 year old who is obese has an 80% chance of living an unhealthy life as an obese adult. So, as CSN once said, “Teach Your Children Well.”

Good luck and good health!