Even though your child’s pediatrician will measure your child’s BMI as part of their annual physical exam, this measurement does not paint a complete picture of your child’s health. As the American Academy of Pediatrics (AAP) states: “A child’s BMI is a valuable screening tool, but it’s only one piece of the puzzle to finding out if a child is at a healthy weight.” BMI takes weight, height, and age into account, but many other factors play a role in body mass, including genetics and metabolism. For this reason, to truly capture your child’s overall health, pediatricians not only consider your child’s BMI, but also their growth trends, body size and type, activity level, diet, and other factors to truly assess a child’s overall health and wellness. “When determining the overall health and nutrition status of a child, we always look at the full clinical presentation,” says Hanna Leikin, MS, RD, CSP, LD, a pediatric dietitian at Cleveland Clinic Children’s. “If a child is overweight or underweight but their weight for age is following historical trends on their growth chart, we will take that into consideration when determining their treatment plan and diagnosis.” Read on to learn more about BMI, including how accurate it is and how to talk to your child’s pediatrician about it. You will also discover the risks of focusing too much on BMI.
What Is BMI?
BMI (or body mass index) is a calculated measurement of a person’s weight in relation to their height. The number that is generated from the calculation serves as a quick tool for healthcare professionals to determine whether someone is at a healthy weight, underweight, overweight, or in an obesity weight range. In children, BMI is usually not calculated under the age of 2 because it is more difficult to accurately measure at this age, says Benjamin Levinson, MD a pediatric primary care physician at Nationwide Children’s Hospital. Once a child is over the age of 2, a pediatrician will look at a child’s BMI as one piece of information in the overall picture of a child’s health. “[In general], BMI just evaluates a child’s weight relative to their height,” adds Dr. Levinson. “It does not evaluate what portion of the weight is lean body mass or body fat, the distribution of the body fat, and any other metrics that would help determine a child’s health status—such as fitness level or metabolic abnormalities.” It is also important to note that BMI for children is different than BMI for adults. Not only is it calculated differently, but it is also expected to change. After all, kids are growing and developing, so their BMI will not be a single data point. Instead, healthcare professionals use BMI percentiles to consider a child’s growth and development and figure out if they are within their healthy weight range. “In pediatrics, we evaluate BMI or growth trends over time to get an accurate assessment,” Leikin says. “And in adults, they evaluate one data point.”
How Accurate Is BMI for Kids?
Although calculating a child’s BMI is a valuable screening tool, it is important to note that it is only a small piece of the entire picture. Other factors like genetics, body composition, age, ethnicity, physical activity, and more must also be considered when determining a child’s health status. “Genetics play a major role in ‘growth velocity,’ which is the trajectory and projected height and weight trend of a child,” says Lauren Beth Cohen, MS, RD, LDN, a Philadelphia-based pediatric registered dietitian and licensed dietitian nutritionist. “Lifestyle factors such as a balanced diet, physical activity, and socialization—to name just a few—all contribute to overall childhood development and wellness. " Plus, while useful, BMI is not a perfect measurement. For instance, kids with a more muscular build might have a high BMI but very little body fat. Or a child may have a lower BMI but not make nutritious eating choices. “BMI, as a single number, in pediatrics is relatively meaningless,” adds Cohen. “Consider a BMI of 12. In the adult population, that person would seem emaciated. In pediatrics, that happens all the time. The number itself is plotted onto a growth chart and expressed as a percentile. The BMI percentile can be a valuable tool in assessing the health of a child.” It’s also important to note that percentiles, as expressed in growth charts, depict the typical growth pattern of children from birth to age 20, Cohen explains. When BMI is plotted on the growth chart, it is given a number between 1 and 100 with the 1st percentile being the smallest and the 100th percentile being the largest. “What is important to recognize is that all percentiles are considered healthy,” Cohen says. “As a pediatric dietitian, I focus on consistency. I like to see a child track on the same percentile throughout their childhood, whether that is the 5th percentile or the 95th percentile.”
How to Talk to Your Child’s Pediatrician About BMI
If you are concerned about your child’s BMI, or if you simply want more information, it is important to talk to their pediatrician. They are the best source for determining whether your child is at a weight that is right for them. Many times, BMI is a great starting point that can lead healthcare providers to investigate further why the number may not be in line with what they expected. For instance, other testing may be done or bloodwork drawn to determine if there are endocrine issues or metabolic abnormalities, for example. But, BMI on its own is just a number and does not define a child’s health, Dr. Levinson says. “When it is elevated this can be a great indication that a more detailed examination of a child’s nutritional and physical activity habits is warranted to help determine what changes should be made to work towards better future health outcomes,” he says. Keep in mind, too, that as your child goes through puberty, their BMI will change. During puberty, your child is making the physical transformation from child to adult, which is characterized by increases in height and weight, completion of skeletal growth, increases in bone mass, changes in body composition, and sexual maturation, says Leikin. “During adolescence, a female’s body fat increases while their lean mass decreases, which is the opposite effect for males,” she says. “Changes during puberty will likely increase the child’s BMI number but it does not necessarily change the BMI percentile.” Also, be mindful about how you discuss the topic of weight with your child’s pediatrician, especially if your child is there listening. You also should consider how much time you spend discussing weight in the home as well. Weight can be a very sensitive topic for children, says Leikin. “Weight talk or weight stigma can increase the risk for anxiety and depression, which can ultimately lead to eating disorders, such as anorexia nervosa, binge eating, and also obesity,” she adds. “It is crucial for the parent and also the clinician to be thoughtful and careful when discussing weight. I personally like to focus on improving how a child feels physically (energy) and emotionally (mood) versus how a child looks or the actual number on the scale.”
Risks of Focusing on BMI
While it can be tempting to get stuck on your child’s BMI, it is important to remember that this is just a single measurement and does not provide a complete picture when it comes to your child’s health and well-being. Instead of focusing on your child’s weight or BMI, center your attention on providing nutritious meals, teaching your child to make nutritious choices, and allowing for body autonomy. “Studies generally show that when parents focus on weight—and by extension, BMI—it leads to worse outcomes for a child’s health, both physically and psychologically,” says Dr. Levinson. “In contrast, focusing on healthy behaviors—like eating fruits and vegetables, decreasing snack food consumption, doing something to be physically active that is enjoyable—generally leads to improved physical and psychological health outcomes.” It may be a concern if it seems your child is zeroing in on getting their body weight to a specific number. This can be a risk factor for some issues. For instance, kids can develop anxiety and depression over the number on the scale. There is even a risk of developing an eating disorder. “Focusing too heavily on BMI can promote a variety of disordered eating behaviors including restricting, binging, and orthorexic tendencies,” says Julia M. Chamberlain MS, INHC, LMHC, a licensed mental health counselor who also holds a health coaching certification from the Institute of Integrative Nutrition. “Since BMI does not specifically measure body fat, it may not always accurately gauge if there is a weight concern. BMI is only one piece of a larger picture.” By contrast, if a child has a “normal” BMI but is engaging in unhealthy eating and physical activity habits, a parent may dismiss this as a concern due to the BMI being in the normal range, says Dr. Levinson. This situation also is not ideal because these unhealthy habits can still lead to worse health outcomes over time. “I encourage parents to focus on improving their child’s wellbeing through increased energy to help with school and extracurricular performance and improving mood through positive self-talk,” says Leikin.
A Word From Verywell
Although BMI is a tool that is used frequently in clinical settings, it is important to note that it is only a single measurement in the overall picture of your child’s health. Instead of focusing on your child’s BMI—or even their weight—direct your attention toward providing nutritious meals and promoting physical activity. These two components are the most important part of a balanced lifestyle and will serve your child well throughout their life. If you do have concerns about your child’s weight and BMI, speak to your child’s pediatrician or a registered dietitian. They can provide insight and guidance that can help you make sense of these numbers and what is right for your child. And be mindful about how you discuss weight—both yours and your child’s. It is easy for these messages to be misconstrued by children and lead to unhelpful concerns later.
