Can a Baby Ever Be Too Fat?

Sure, baby rolls are adorable, but in this age of skyrocketing childhood obesity rates, they can also be worrisome. Our guide to growth charts can help you relax.

Chubby Newborn at Doctors Office Shutterstock
"Clearly you’ve got a good eater.”

“Looks like a future defensive end there.”

“Pork-chop thighs!”

These are just some of the comments friends, and even strangers, made about my son when he was a baby. Nate was indeed a big guy. At 9 months, he was 25 pounds and measured 31 inches, putting him in the 100th percentile for weight and the 99th for height. It was a challenge keeping him in clothes and diapers that fit, and my mother, who is 5 feet tall in heels, couldn’t even lift him.

She would still try, exclaiming, “Healthy boy!” Mom clearly took pleasure in Nate’s size—and his robust appetite. In our Korean culture, there’s no such thing as overfeeding your child, and once Nate started eating solids, she was over the moon, spoon-feeding him to the brink of bursting. My mother-in-law, who is Jewish and not known for serving modest portions either, was the same way: While neither grandma has ever bathed Nate, dressed him, or changed his diaper, both fed him breakfast, lunch, and dinner when they were with him. 

Still, people’s comments about Nate’s size started to get to me. His being in the 99th percentile for height seemed like an amazing thing to a short person like me. But for weight? I wasn’t sure if that meant Nate was technically overweight, and I worried that I was raising him to be fat and unhealthy. Then I saw a study from Wayne State University, in Detroit, which found that babies who were obese at 9 months were three times more likely than healthy-weight 9-month-olds to be obese at ages 2 and 4, and I set out to understand his newborn growth chart. Here’s what I learned. 

Growth Charts Aren't New

Back in the late 1970s, the National Center for Health Statistics collected the weight, height, and head circumference of American children from the age of 1 month to 2 years old. The data was crunched separately for boys and girls, and charts were created to show the distribution of weight, length, and head circumference for age, and of weight for length. The curved lines on standard charts trace the growth of kids in the 3rd, 5th, 10th, 25th, 50th, 75th, 90th, 95th, and 97th percentiles. The aim was to show through data how healthy children grow, so that children who were growing at unexpected rates could be identified. “Historically, the charts were used for babies who were underweight and failing to thrive,” says Emily Oken, M.D., M.P.H., professor of population medicine at Harvard Medical School. “Now the focus is more on big babies.”

There Are Two Sets of Charts

One set is from the Centers for Disease Control and Prevention (CDC). It was last revised in 2000, and many doctors still use it. There’s also a set of growth charts from the World Health Organization (WHO), last updated in 2006. This is the one the National Institutes of Health and the American Academy of Pediatrics suggest pediatricians use. The reason: The WHO charts have data from healthy, breastfed-only babies around the world, while the CDC charts are based on both breast- and formula-fed babies from the U.S. only. “Breastfed-only babies are a better standard because they are less likely to be overfed,” says Nancy Crimmins, M.D., a pediatric endocrinologist at Cincinnati Children’s Hospital Medical Center. Confirm with your pediatrician which set of charts she uses. I asked my doctor and found out she still uses the CDC ones, primarily because she’s not ready to change her record-keeping system. However, if she’d used the WHO charts, Nate’s 9-month percentiles would have been virtually the same: 99.6th for weight and 100th for length. 

They Reveal Helpful Info

A healthy baby can fall anywhere on the grid. What matters more is if the percentile for height and weight are similar. “Obviously, an extra-long baby will be heavier than most,” Dr. Crimmins notes. “Likewise, a baby in the 10th percentile for length is going to weigh less than most.”

Yet even when the two percentiles aren’t close—say 50th for length and 75th for weight—you may not need to worry. “As long as a child’s weight is around the same percentile at each well visit, and he’s hitting his milestones, I wouldn’t be especially concerned,” says Dr. Crimmins. “The red flag is when a baby zooms across percentiles, from say the 25th to 50th to the 75th, which suggests he’s gaining too quickly.”

Ask your doctor to share your baby’s weight-for-length percentile too. It can help you make sense of the other numbers, since a longer baby will tend to weigh more and a shorter baby to weigh less. For instance, even though Nate was in the 99th percentile for weight for his age, he was in the 85th percentile for weight for length, putting him in the healthy range for this measurement.

Once your baby turns 2, your pediatrician may stop using either chart and calculate your baby’s body mass index (BMI). BMI is considered a more accurate measure of body fat going forward. In fact, some doctors are now looking at BMI in infancy. 

Start a Convo

Even if my doctor had been concerned about Nate’s size, it’s a big mistake to put a baby on a diet. “Babies grow so rapidly that we don’t want them to lose weight,” Dr. Crimmins notes. “Instead, we would try slowing down the rate of weight gain.” So when you doctor goes over your baby’s chart, ask all your feeding questions, whether about supplementing with formula, the number of feeding sessions a day, or when to offer solids. As for Nate, he started to lose some of his cute chunkiness at about 12 months, and once he began walking, he trimmed down again. But one thing hasn’t changed: His grandmothers still happily ply him with home-cooked food, eager to see him smile.