What is Body Mass Index?

Body Mass Index (BMI) is a ratio of weight to height. It is a screening tool for spotting people who are more likely to develop various health problems from over or underweight, and for tracking that development in children is progressing appropriately. In adults, a BMI Between 18.5 and 25 is considered healthy. Below 18.5 is underweight. Higher than 25 is overweight; higher than 30 is obese.

In children, the BMI is expressed not only as a number, but as a percentile rank. The child or teen is plotted against other kids of the same age. A child who has a BMI greater than 85 percent of children her age is considered overweight; greater than 95 percent is considered obese. A BMI of less than 5 percent is considered underweight.

There is a very wide range of weights that are considered healthy for a given height in children and adults. Juliana’s healthy weight range is between 93 and 136 pounds. My healthy weight range is between 121 and 171 pounds.

Healthy doesn’t mean ideal for the individual. Although a BMI of 24 is considered healthy, most adults will feel better at a much lower BMI. The same is true for children–although a BMI in the 84th percentile will not technically indicate a child is overweight, that child will likely feel better at a lower BMI.

Calories In/Calories Out–NOT

The calories in/calories out model of weight management says: burn more calories than you consume to lose weight; –balance calorie consumption with expenditure to maintain weight.  Like the public health ad said that I remember from the Washington subway in the late 90′s:  switch from mayonnaise to mustard on your daily sandwich and lose 10.4 pounds a year (savings of 100 calories/day for 365 days).  The CDC recommends that children get 60 minutes of moderate intensity physical activity on most days of the week, and preferably every day.  For a 154 pound person, they estimate that 60 minutes of brisk walking (4.5 mph) will burn 460 calories an hour (more if you are heavier, less if you are lighter).  That’s 3220 calories per week, or 47.8 pounds of expected weight loss over a year.

Virtually all of the dietary advice provided to parents who are trying to help their children achieve or maintain a healthy weight conforms to this model, the most recent and visible example being Michelle Obama’s Let’s Move initiative, which is closely tied to the USDA’s new food plate eating plan, and replaced the earlier pyramid eating plan.  Both the new Food Plate and the old Pyramid are high carb, low fat eating plans.

These diets were recommended by public health authorities beginning in the 1980s because it was believed such a diet was beneficial for preventing heart disease, while at the same time controlling weight because it was supposed to be a relatively low calorie diet.  Carbohydrates have fewer calories per gram of weight (4) than fat (9) and the same as protein (4).  It was further thought that even if the diet itself didn’t turn out to be protective against heart disease, it would control weight, and controlling weight would be protective against heart disease.

There’s just one problem:  high carb, low fat diets like the new food plate and the old pyramid don’t work for weight loss or weight maintenance and don’t improve other health markers either.   Gary Taubes, in the lengthy “Good Calories, Bad Calories,” and the cliffs notes version “Why We Get Fat and What to do About it,” eviscerates the logic behind low fat, high carb diets.  Reading these books completely changed how I thought about Juliana’s struggle with weight.   If you eat like the USDA pyramid and are a normal weight, your body can handle a high level of carbohydrates (for now at least)–the evidence for that is that you are a normal weight.  Your child can’t, and that is why he or she is overweight.

If you are a normal weight adult trying to help an overweight child, you should run to the library or bookstore for these books.

We tried exercise…and tried…and tried…

Juliana was lethargic from a young age. I wasn’t sure why parents were always taking their kids to the park–even before she became obese, Juliana didn’t run around, she sat in the sand. I expanded my efforts to get her to move. She did gymnastics, swimming lessons, and soccer. She played basketball and indoor soccer in the winter. She joined a swim team in the summer. We tried softball because it was one of the few sports available in the spring, but it had a terrible driving to exercise ratio–lots of driving, very little exercise, so we stopped.

When she was in third grade, I started the first Girls on the Run program in our town. She ran her first 5k. Then she ran more races. Then she joined a kids triathlon team, and did triathlons too. When she was 12, she ran a 10k race by herself. We did kids’ weight training at home, since muscle mass is supposed to boost metabolism, and is also good for reducing sports related injuries.

Although exercise seemed to help her mood, a lot, it did not help her achieve a healthy weight.  It did not even seem to slow her weight gain.