As anyone who has been to a doctor knows, a standard part of a doctor’s visit or wellness exam is determining a patient’s BMI. But what exactly does “BMI” mean? And what can it tell clinicians about their patients?
Body mass index (BMI) is a measure of body weight adjusted for height. While BMI isn’t foolproof, it is generally considered a useful way of determining whether or not someone is obese. Obesity can lead to a number of negative health conditions, from high blood pressure to joint issues to diabetes.
To calculate BMI, divide a person’s weight (in pounds) by their height (in inches) squared, then multiply the result by 703. Or simply use a BMI calculator! Interpreting the results is simple for adults over 20 years of age, because standard categories apply. For example, the normal range is between 18.5 and 24.9, while the overweight category runs from 25.0 to 29.9. To interpret BMI numbers in children and adolescents, age and gender must be taken into account.
According to the CDC, obesity has doubled in children and tripled in adolescents in the past 30 years, with 18 percent of those aged 12-19 classified as obese in 2010. Obese children and adolescents are at risk for developing health problems later in life, including diabetes.
But a recent study involving Children’s Hospital researchers found that teenagers who lowered their BMI by 8 percent or more had improvements in insulin sensitivity, an important metabolic factor related to the later development of type 2 diabetes. The teens followed a family-based, lifestyle-modification weight loss program.
“This threshold effect that occurs at 8 percent suggests that obese adolescents don’t need to lose enormous amounts of weight to achieve improvements,” said pediatric endocrinologist Lorraine Levitt Katz, MD, of the Diabetes Center for Children at The Children’s Hospital of Philadelphia. The findings were published recently in The Journal of Pediatrics.
The study team analyzed results in 113 primarily urban adolescents, aged 13 to 17, of whom 81 percent were female and 62 percent were African American. At the start of the study, their mean BMI was 37.1, placing them in the severely obese range. None had type 2 diabetes, but their obesity placed them at high risk for developing the disease in the future.
An important goal of the study was to determine the threshold of weight loss that significantly impacted insulin sensitivity, glucose tolerance, and the presence of metabolic syndrome (MS), which is also associated with the development of type 2 diabetes. In type 2 diabetes, the body is unable to produce enough or properly use insulin. Improved insulin sensitivity reflects a better ability to process insulin.
The main finding of the current study was a significant improvement in all measures of insulin sensitivity. There was also a trend toward improvement in metabolic syndrome. Importantly, while the ideal goal is to achieve normal weight levels, children do not need to be skinny to see improvements. The 8 percent reduction in BMI is achievable, and BMI is easy for primary care physicians to track, according to the investigators.
The weight loss program used family-based lifestyle modification. Clinicians taught the teens and adults who took part in the study about healthful eating habits and encouraged them to increase physical activities, such as walking, climbing stairs, and engaging in sports. Some of the teens used portion-controlled, prepackaged foods, while others ate regular food but followed a calorie-restricted, nutritionally balanced diet.
“This study reinforces the importance of behavior change — adopting healthy eating habits and getting more physical activity — in achieving weight loss in adolescents,” added Robert I. Berkowitz, MD, the director of CHOP’s Weight and Eating Disorders Research Program.