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Baby BMI? You’ve Got to Be Kidding

Why you might hear your pediatrician mention this and what to do

Published on: August 23, 2017

Baby on scale

Michelle Reich of Tacoma had no concerns about her firstborn daughter’s weight. Her 7-and-a-half-pound newborn Hannah had quickly blossomed into a healthy, precocious toddler with rosy cheeks, sparkling hazel eyes and dark-blond curls. True, Hannah was larger than some of her peers, but that seemed like a positive sign, says Reich. “She elicited coos of ‘What a yummy baby with all those rolls!’” she says. “I had no reason to believe her weight was anything but an asset.”

But at Hannah’s two-year checkup, her doctor seemed to disagree. She got right down to business, replaying Hannah’s height and weight stats with a critical pause between the two: 75th percentile for height…but…99th percentile for weight. Not off the charts, but almost. Then, a pointed question: “Is she active?” 

“It felt like a thinly veiled accusation,” Reich says. “It was the first time I felt like I had to justify her weight.’” Reich left the visit with a chart listing Hannah’s BMI as overweight and a looming worry: Did Hannah’s adorably soft arms and rounded belly signal future weight worries? Should Michelle be watching her calorie intake? It seemed crazy, she recalls. “I kept thinking, she’s 2!”

Nobody wants to be hassled about their child’s weight. And judging sweetly squishy thighs and chubby cheeks by a grown-up metric like BMI (or body mass index, a measure of weight divided by height squared) just seems wrong. Some say it is: Because BMI is a two-dimensional measurement of body mass that doesn’t take into account the fact that humans are three-dimensional, or account for differences in age and build, critics say the equation doesn’t add up, and that BMI needs to be reworked in order to have validity as a health measurement. 

While a measurement like BMI can help track health trends in a general population, it’s trickier to apply at an individual level.

And even if BMI is a valid tool, having one on the higher side isn’t necessarily bad; doctors see plenty of patients with a high BMI and otherwise stellar health, and the BMI of athletes with fit, strong bodies can label them as obese. But Hannah’s doctor’s concern wasn’t completely unfounded. Over the last decade, a number of studies have shown a link between BMI in early childhood and obesity later in life. A new study shows that a child’s BMI at ages 1 and 5 may be predictive of future weight.

Bodies are beautiful in any shape and size and having one that’s particularly big or small isn’t problematic; obesity, however, is linked to an increased likelihood of having diabetes, sleep apnea, high blood pressure and stroke — health problems parents would just as soon help their kids avoid if possible. With U.S. obesity reaching epidemic levels, more pediatricians are taking note of babyhood body mass and asking nonplussed parents to watch the scale.

The problem, says pediatrician Dr. Yolanda N. Evans of Seattle Children’s Hospital, is that overall health is more important than numbers on a scale. So while a measurement like BMI can help track health trends in a general population, it’s trickier to apply at an individual level. 

It’s true that larger children tend to grow into larger adults and some of those adults will be obese, says Dr. Evans. But BMI is not a foolproof metric for kids, particularly those under 2, she says. “BMI varies by gender and ethnicity and cannot differentiate between fat and muscle, so solely basing clinical recommendations on BMI may not be accurate.”

And it’s not necessarily body weight itself but a steep weight increase in the first year of life that could point to future weight struggles, according to this study

Instead of focusing on the scale, Dr. Evans says, “health care providers should review each individual patient’s growth charts to look for deviations in trends. If a child’s BMI is increasing rapidly, or falling rapidly, guidance should be given.”

When, like Reich, you have a kid with a healthy lifestyle — high on physical activity, low on junk food — and a higher BMI, don’t stress, Dr. Evans says. “A hyper-focus on numeric measures of fitness can be harmful, particularly if it leads to shaming comments or an overly restrictive approach to food,” she says. “I encourage parents not to think about BMI or the number on the scale. Instead, consider gradual behavior changes toward a healthier lifestyle.” 

These days, Hannah is a bubbly, active 6-year-old with a 1-year-old baby sister, who’s also a thriving, happy girl at the top of the pediatrician’s weight charts. Though Reich still fields “That’s a big baby!” comments, she takes weight-related guidance with a grain of salt. “We focus on exercise for pleasure, no soda, little processed food. I know my girls are growing the way they were genetically designed to.” 

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