"What's the right weight for my child?" is one of the most common questions
parents have. It seems like a simple one, but it's not always easy to answer.
Growth and Puberty
Not everyone grows and develops on the same schedule. During puberty,
the body begins making hormones that spark physical changes like breast development
in girls, testicular enlargement in boys, and spurts in height and weight gain in
both boys and girls.
These changes continue for several years. The average kid can expect to grow as
much as 10 inches (25 centimeters) during puberty before reaching full adult height.
Because some kids start developing as early as age 8 and some not until age 14,
it can be normal for two kids who are the same gender and age to have very different
weights.
What Is Body Mass Index?
Body mass index, or BMI
for short, is a formula that doctors use to estimate how much body fat someone has.
The BMI formula uses height and weight measurements to calculate a BMI number. Though
the formula is the same for adults and children, figuring out what the BMI number
means is a little more complicated for kids.
For kids, BMI is plotted on a growth
chart because what is normal changes with age. Different BMI charts are used for
boys and girls because growth rate and the amount of body fat differs between boys
and girls. Each BMI chart is divided into percentiles that compare measurements with
children the same age and gender.
The categories that describe a person's weight are:
Underweight: BMI below the 5th percentile age, gender, and height.
Healthy weight: BMI is equal to or greater than the 5th percentile
and less than the 85th percentile for age, gender, and height.
Overweight: BMI at or above the 85th percentile but less than
the 95th percentile for age, gender, and height.
Obese: BMI at or above the 95th percentile for age, gender, and
height.
Before you calculate your child's BMI, you'll need an accurate height and weight
measurement. Bathroom scales and tape measures aren't always precise. So the best
way to get accurate measurements is by having kids weighed and measured at a doctor's
office or at school.
What Does BMI Tell Us?
You can calculate BMI on your own, but consider asking your doctor to help you
figure out what it means. Doctors do more than just use BMI to assess a child's current
weight. They also take into account stage of puberty and use BMI results from past
years to track whether a child is overweight. Spotting trends early on can be helpful
so you can make changes before weight gain becomes a problem.
Overweight and obese kids and teens are developing weight-related health problems,
such as type 2 diabetes, high cholesterol,
and high blood pressure (hypertension).
Overweight teens are
also more likely to be overweight as adults. And adults who are overweight have a
greater chance of serious health conditions, such as heart disease.
Although BMI can be a good indicator of body fat, it doesn't always tell the full
story. Someone with a large frame or a lot of muscle (like a bodybuilder or athlete)
can have a high BMI but not too much fat. Likewise, a small person with a small frame
may have a normal BMI but could still have too much body fat. These are other good
reasons to talk about your child's BMI with your doctor.