At my son’s yearly physical a few weeks back, the doctor told me he was concerned about my child’s BMI (Body Mass Index). Although I know he grew recently and gained weight, I’m not concerned. I’m also not making any changes. You can read more about this problematic doctor’s visit HERE.

As a mom and dietitian, parents often ask me if they should be concerned about their child’s BMI, especially if it’s at either end of the growth curve. This is most common for kids considered “overweight” or above the 85th percentile for BMI.

Why You Shouldn’t Be Concerned About Your Child’s BMI

BMI WAS NOT INTENDED TO MEASURE HEALTH

BMI is an individual’s ratio of height to weight. The BMI formula was developed by a Belgian mathematician and astronomer, not a physician or healthcare provider. It was originally intended to measure a population’s height and weight distribution. It was never meant to assess an individual’s health.

In 1972, Ancel Keys, who studied body mass and composition, published a paper in which he termed the body height to weight ratio, BMI. In the early 1990’s the World Health Organization (WHO) established standard BMI categories to classify individuals as “underweight”, “normal”, “overweight”, and “obese.”

According to the CDC (Centers for Disease Control and Prevention),

BMI can be used to screen for weight categories that may lead to health problems but it is not diagnostic of the body fatness or health of an individual.

Despite this warning or suggestion, many healthcare professionals make assumptions and recommendations about health based on BMI. And in direct contradiction to the CDC statement, BMI determines a medical diagnosis.

An additional concern about your child’s BMI is that Keys did not study children. His findings are based on his research on adult males.

CHILDREN GROW AT VARYING RATES

The BMI for children is based on percentiles. First, calculate the BMI based on the formula, then compare it to individuals of the same age and gender. Children in the highest percentile are “obese” or “overweight” and those in the lowest 5th percentile “underweight”.

Children’s health is being based on their body size compared to their peers at any given moment. Does that sound absurd to you? Not only is it absurd to assume children at the ends of the spectrum are automatically “unhealthy”, but children grow at different rates. Children tend to gain fat or “fill out” before they grow in height. While there might be some expectation of growth rates, children will never all grow at the same rate.

INDIVIDUALS HAVE DIFFERENT BODY SIZES AND SHAPES

Research suggests that genetics primarily determine body size. Some people will naturally be wider and others taller. These variants do not inherently predict one’s health. Folks in the “overweight” category, who therefore inhabit a wider body, live longer than folks in the “normal” weight category. These differences in body size are merely differences, not health-related. For more information, read Weight Science: Evaluating the Evidence for a Paradigm Shift.

OTHER FACTORS ARE GREATER DETERMINANTS OF HEALTH THAN YOUR CHILD’S BMI

As outlined in the book Body Respect by Lindo Bacon and Lucy Aphramor, genetics, socioeconomic class, and weight stigma are all determinants of health. When these factors are controlled for, weight is not an independent factor of health. Further, when individuals make lifestyle behavior changes, such as increased activity or eating more produce, they experience improved health outcomes even when weight doesn’t change.

THE CONSEQUENCES OF TRYING TO CONTROL WEIGHT ARE HARMFUL

Even if you’re still concerned about your child’s BMI, consider the consequences. When parents attempt to control their child’s weight, their weight typically spikes. This occurs because children feel deprived, are not being fed adequately for their caloric needs, and detach from their body cues. They sneak and hide food, eat as much as possible when it is available, and choose more forbidden foods.

Those are the rebound consequences. However, children that diet are more likely to develop eating disorders, weight cycle, and again, end up in larger bodies.

You might find it hard to believe weight isn’t a great indicator of health. That’s normal and hard to challenge because of the constant emphasis on weight loss and health. Deconstructing this paradigm requires a different way of thinking. Much of the research supports that the Health at Every Size® model and Intuitive Eating are health-promoting, the opposite of pursuing weight loss.