Looking to improve your health? Know your BMI

Image courtesy United States Department of Agriculture Food and Nutrition Service.
Image courtesy United States Department of Agriculture Food and Nutrition Service.

Throughout the month of March, Momentum will be featuring health and wellness information in celebration of National Nutrition Month.

Looking to get a read on your health? Start with your weight and body mass index, commonly referred to as your BMI.

“The BMI is a weight to height ratio, that is a way to tease out what your weight implies,” said Roman Shypailo, instructor in the USDA/ARS Children’s Nutrition Research Center at Baylor College of Medicine. “It’s a simple ratio that anyone can use.”

Not a math wizard? The CNRC has developed a calculator for both children and adults to easily calculate their BMI using age, height and weight.

Explore the interactive BCM calculators for children and for adults.

Adult BMI

For adults, interpreting BMI is pretty standard and straightforward:

  • If your BMI is under 25 you are considered to be at a healthy weight.
  • If your BMI is between 25 to 29.9 you are considered overweight.
  • If your BMI is 30 or more you are considered obese.

Shypailo notes there is a caveat: professional athletes with incredible muscle mass, like NFL defensive ends (think JJ Watt), can have a BMI that would place them in the obese range even though many are in shape and incredibly healthy and fit.

“For most adults, BMI is an estimate of where you are with your weight and can send up a warning sign as you pass a BMI of 25, a red flag that can prompt you to watch what you’re eating and start exercising more,” Shypailo said.

Kids BMI

Interpreting BMI for children is different than adults. As they develop and grow, the numbers shift.

Instead of flat numbers, BMI scores for kids are given in percentiles based on age:

  • Less than 5 percent suggests the child is underweight
  • Percentiles ranging between 5 and 85 percent suggest a healthy weight for the child
  • 85 to 95 percent suggests the child is overweight
  • Scores equal to or greater than 95 percent suggest the child is obese.

“When you are a kid, what is normal and healthy for BMI changes with age,” Shypailo said. “The range rises over time, for example a 15-year-old with a BMI of 20 means something different than a 5-year-old with a BMI of 20.”

He said a child’s BMI isn’t a final answer or indicator of future obesity; parents need to factor in activity level and body composition. He encourages parents to track their BMI over a time period to notice any trends, which could indicate whether their child is putting on fat quickly and in danger of becoming obese.

On the other end of the scale, Shypailo said BMI could also be a good indicator of when a child is underweight when the score is very low.

“My advice is to check with your pediatrician to see what’s going on,” he said. “If you are concerned if your child is too heavy or too thin.”

Additional Resources

Read more about nutrition research from the CNRC in the center’s newsletter.
Get moving: Our experts offer tips for helping kids be more active.

-By Audrey M. Marks

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