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Healthy Weight for Children: Why You Can't Always Tell by Looking
child-scaleby Vincent Iannelli, M.D., F.A.A.P.

Q. I'm concerned about a 10-year-old male relative who I feel is extremely underweight for his age. He is only 55 pounds and measures about 4 feet 6 inches tall.
Dolores

A. When children don't seem to be growing just right, parents and other family members are often concerned that they are underweight or overweight. But it can be hard to tell just by looking. Instead, we have to consider a variety of factors. The evaluation usually starts—but doesn't end—with the scale and the measuring tape.


STEP ONE: GROWTH, WEIGHT AND BMI

To help us determine what are healthy weights for children, the Centers for Disease Control and Prevention provides growth charts, weight charts and charts that compare body mass index to age. Body mass index gives us an idea of how much fat the child has. Here's how to find it (using your relative as an example):

Formula:
BMI = [weight in pounds ÷ (height in inches x height in inches)] x 703

Example (using your relative):
BMI = [55 pounds ÷ (54 inches x 54 inches)] x 703
BMI = (55 ÷ 2,916) x 703
BMI = 13.26

After calculating a child's BMI, you can look at the CDC's chart to see where the child falls in relation to his or her peers. At minimum, the child should be at the fifth percentile, meaning that about 5 percent of boys his age (or girls her age) have a lower BMI than he does.

In order to be at the fifth percentile, a 10-year-old male should have a BMI of about 14.5 or more (depending on how many months he is into his 10th year). So, if your relative is exactly 4 feet 6 inches, he is underweight, according to the chart.

child-scale-weightBut charts aren't all we go by. Children are individuals, not statistics, so health-care providers must take that into account. Therefore, we also consider other issues when determining whether a child's weight is healthy.


STEP TWO: OTHER ISSUES

Here are some of the other things we look at when evaluating a child's weight:

  • Puberty. Puberty in boys normally begins between ages 9 and 14. If a 10-year-old has already started puberty, he might be going through a growth spurt and be putting on muscle mass, while prepubertal boys would still be on the thin side.
  • Consistency. It's hard to know if a child is growing normally based on a single weight. Instead, pediatricians like to track a child's weight gain over time. It would be a concern if he used to be at the 40th percentile on the CDC's weight chart, for example, and has now dropped down to the fifth.
  • Progression. One red flag that might indicate a medical problem is losing weight or not gaining an appropriate amount of weight over the last few years. For a school-age boy, normal weight gain would be about 5 or 6 pounds a year.
  • Other conditions. It would also be concerning if he had a chronic medical condition, such as asthma or diabetes, that might affect his weight gain, or if he was taking a medication that could affect his growth, such as a stimulant (Ritalin, Adderall, etc.) for attention deficit hyperactivity disorder (ADHD). It would also be a worry if a child didn't eat well or had some kind of chronic symptoms, such as regular fevers, diarrhea, vomiting or frequent urination. Although often overlooked in boys, anorexia can also be a reason for a preteen or teenage boy to be small or underweight. These boys may not eat enough calories, exercise too much and think they're overweight.

Without any symptoms, and if he has a healthy diet and an active lifestyle, and is otherwise growing and developing normally, then a child like this is often not really underweight. A visit to your pediatrician would still be a good idea to make sure. The doctor can review the boy's weight gain over the past two or three years to see if it has been progressing normally and consider testing him for a thyroid disorder, diabetes and other conditions that can affect weight.

Remember that genetics plays a very big influence on how a child is growing. So if a child's parents are both tall and thin, you can expect him to be tall and thin too.


VINCENT IANNELLI, M.D., F.A.A.P.,
is a pediatrician near Dallas, Texas, and the author of The Everything Father's First Year Book. He also runs the pediatric parenting advice Web sites pediatrics.about.com and keepkidshealthy.com.


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Last updated and/or approved: July 2010.
Original article appeared in fall 2006 former print magazine. Bio current as of that issue. This article is not meant as individual advice. Please see our disclaimer.
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