When should parents really be worried about their child’s high body mass index (BMI)?  Gene Emery says before five years old:

Children who are overweight when they start school are far more likely to be obese by the time they become teenagers, according to a new study of nearly 8,000 children.

Overweight five-year-olds were four times more likely to be obese by age 14 than children who started kindergarten at a healthy weight.


This study, published in last week’s New England Journal of Medicine, should make every pediatrician and parent take objective BMI values more seriously at younger ages.

teen-bmi-calculator-boysBMI is calculated by taking a person’s weight and height, plugging it into a mathematical equation*, and then plotting that number on a growth chart that illustrates percentiles.  Any point between the 10th percentile and the 85th percentile is considered normal; between the 85th and 95th percentile is “overweight” and above the 95th percentile is considered “obese.”  It’s been known for a long time that a BMI between the 85th and 95th percentile means a child is at risk for becoming obese later on.  This study, says Alexandra Sifferlin, confirms that notion:


Scientists tracked a group of 7738 children, some of whom were overweight or obese, and some who were normal weight, from 1998 (when they were in kindergarten) to 2007 (when they were in ninth grade). They found that the 14.9% of five-year-olds who were overweight at kindergarten were four times more likely to become obese nearly a decade later than five-year-olds of a healthy weight.


Jacque Wilson has more:

By the eighth grade, 20.8% of the children in the study were obese and 17% were overweight.

Half of the children who were obese at 14 had been a part of the 14.9% who were overweight as kindergarteners; 75% had been in the 70th BMI percentile or above.

The greatest increase in obesity rates was seen between first and third grades when the incidence jumped from 13% to 18.6%.

Children in the wealthiest families were the least likely to be overweight. Children who were born heavier  i.e., more than 8.8 pounds  had a higher risk of being obese at every age.


It’s no secret what causes children and adults to become overweight or obese:  caloric intake (from food and beverages) exceeds caloric output (burning calories from exercise and by your body’s unique metabolic rate).  While the basal metabolic rate can be affected  to some degree by heredity, illness, and medications, taking in and burning off calories is mostly within our control. Not everybody is athletic or inclined to exercise, but most healthy children before the age of five are naturally active. The key to preventing obesity by the time a child is five years old is to encourage activity and to provide appropriate food choices for infants, toddlers, and preschoolers:  fruit instead of refined sugar, milk and water instead of soda and other sugar-sweetened beverages, “nothing” instead of junk.  (Remember, “nothing” can be a choice — “You may have an apple for a snack or you may have nothing.”)  Essentially, providing real food (stuff that comes from trees and plants and the ground and animals who you can readily identify in the item you’re eating, and not processed — packaged — food) that is nutrient dense and low in sugar, salt, and chemicals.

Obesity is preventable.  We can do this.  We just have to start prevention at birth.

More PediaBlog on childhood obesity here and nutrition here.


*BMI= weight (kg) / [height (m) x height (m)]


BMI = weight (lbs) x 703/ [height (in) x height (in)]