How Much “Weight” to Put on Your Child’s BMI

Paige Mandel, MS RD CDN

 

Body Mass Index (BMI) is often a point of confusion for many parents and kids alike. Should we pay much attention to it or not? “My child’s pediatrician said he/she is overweight, do I need to put them on a diet?” “What does it mean if my child is considered underweight/overweight/obese?” Are often questions we get as dietitians from concerned and proactive parents. Basically, any classification outside of “normal weight” raises an eyebrow and gets the mind running for parents, caregivers and the child themselves.

 

Keep in mind, BMI is simply a mathematic formula developed in the 1830’s by a Belgian statistician that equated to taking your weight (in kilograms), and dividing by the square of your height (in meters). “The result, which slots you into one of four main categories, is meant to describe your body in a single word or two: underweight (BMI less than 18.5), normal weight (18.5 to 24.9), overweight (25.0 to 29.9) or obese (30 or greater)”1. Although calculated the same, BMI is interpreted slightly different for children and teens, varying by age and sex2. “Due to changes in weight and height with age, as well as their relation to body fatness, BMI levels among children and teens are expressed relative to other children of the same sex and age. These percentiles are calculated from the CDC growth charts, which were based on national survey data collected from 1963-65 to 1988-944.”2 Similarly, the result is into one of four categories: underweight (less than the 5th percentile), healthy weight (5th to 85th percentile), overweight (85th to 95th percentile), or obesity (95th percent or greater)3.

 

An example of a BMI growth chart is represented below:

2

 

At LCWNS, we think the measurement called Body Mass Index is overrated, antiquated, and has the potential to misdiagnose ourselves and our kids4. On it’s own, it has the power to create a vision of health status, with not much validity or information to it.

 

In research, this is a helpful tool to generalize a population for correlated health outcomes or behaviors, yet for the individual, it’s pretty meaningless. BMI and growth chart percentiles do not give any information on body composition i.e., muscle mass, fat mass, bone structure, just simply their weight for their height. The healthcare system still uses this measure as a standard for data comparison, but it is not an evaluation of health status. “ In a 2016 study of more than 40,000 adults in the United States, researchers compared people’s B.M.I.s with more specific measurements of their health, like their insulin resistance, markers of inflammation and blood pressure, triglyceride, cholesterol and glucose levels. Nearly half of those classified as overweight and about a quarter of those classified as obese were metabolically healthy by these measures. On the other hand, 31 percent of those with a “normal” body mass index were metabolically unhealthy”1,5. This is one of many studies that highlights the misclassification of health in relation to BMI.

 

Unfortunately, while some are, many pediatricians may not be weight-sensitive or trained in eating disorders and the nuances of preventing them. Therefore, it is most important to actually understand the facts and advocate for a weight neutral approach to your child’s care. If weight is of concern to the doctor, seek professional advice from a registered dietitian, who will holistically evaluate your child’s needs, behaviors, and beliefs to guide you to take the appropriate next steps.

 

At the end of the day, it always comes back to this same question: “What can we as parents do to prevent disease?” This includes obesity-related disease.
I recognize we need measurements for statistic purposes and possibly diagnostic tools. However, I think BMI should be emphasized less and instead we can focus on behaviors and a cluster of measurements.

 

As parents, healthcare facilitators and makers of change, we must remember that obesity does not always equate with overeating, high cholesterol and/or inactivity. Additionally, must remember that BMI is not a measure of self-worth. Rather, it’s merely one tool that aims to measure health—and a flawed tool at that4.

 

At LCWNS we are here to help guide you and your family toward size-acceptance, promoting confidence and self-esteem in our children. We propose to start with the following:

  • Foster a positive opinion of food in the household.
  • Feed your children a balanced intake of whole grains, lean proteins and heart healthy fats.
  • Tell your children you love them. Have them look in the mirror and tell themselves they are loved. Tell them they are more than a number.
  • Encourage healthy behaviors by setting an example.
  • Focus on your children’s efforts and behaviors, not on outcomes or measures. Praise them for trying a vegetable or sport rather than for being a veggie eater or a great baseball player.

 

 

References:

  1. Callahan A. Is B.M.I. a Scam? The New York Times. https://www.nytimes.com/2021/05/18/style/is-bmi-a-scam.html. Published May 18, 2021. Accessed May 18, 2022.
  2. CDC. About Child and Teen BMI. Centers for Disease Control and Prevention. Published April 12, 2022. Accessed May 18, 2022. https://www.cdc.gov/healthyweight/assessing/bmi/childrens_bmi/about_childrens_bmi.html
  3. CDC. BMI for Children and Teens. Centers for Disease Control and Prevention. Published December 3, 2021. Accessed May 18, 2022. https://www.cdc.gov/obesity/basics/childhood-defining.html
  4. Laura Cipullo, RD | Too Much Weight on BMI. Accessed May 18, 2022. https://lauracipullo.com/too-much-weight-on-bmi/
  5. Tomiyama AJ, Hunger JM, Nguyen-Cuu J, Wells C. Misclassification of cardiometabolic health when using body mass index categories in NHANES 2005–2012. Int J Obes. 2016;40(5):883-886. doi:10.1038/ijo.2016.17


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