Those who are closely watching their weight are familiar with the term BMI, short for body mass index. Body weight in absolute terms cannot be used as accurate measure of obesity for simple reason that there are short people and there are tall people, and weight can therefore vary relative to height. That’s why scientists use BMI, a numerical value of weight in relation to height, calculated as a person’s body weight divided by the square of his or her height, as a diagnostic tool to evaluate weight problems and health status of a person. Weight status based on BMI (usually expressed in terms of kg/m2) is categorized as follows:
- Underweight – 18.5 and below
- Normal weight – 18.5 to 25
- Overweight – 25 to 30
- Obesity class I – 30 to 35
- Obesity class II – 35 to 40
- Obesity class III – above 40
This has been like this for years but recently, there have been concerns that BMI may not be an accurate way of assessing a person’s true health status.
Based on BMI measurements, almost one-third of the American population is considered overweight, which is the middle range between normal weight and obesity. Excess weight has been identified as a major risk factor in many chronic diseases, including heart disease, hypertension, hyperlipidemia, diabetes, osteoporosis and certain types of cancer.
Several research studies looked at how BMI is related to mortality rates, were surprisingly inconclusive and sometimes contradictory results. Scientists now think that that BMI may not be the right measurement because:
- BMI doesn’t distinguish between different types of fat mass. For example, there is the fat mass which is of important health concerns as it is closely linked to type 2 diabetes. However, there is also lean mass, especially muscle tissue, which reduces health risks.
- BMI does not directly measure the distribution of body fat. Depending on location, fat may have more or less impact on health. Visceral fat or fat at the waist, for example, is more detrimental to health than fat at the hips.
Thus, using BMI as health status indicator does not actually show the complete picture and may miss the health risks that slight overweight may present.
According to lead author Dr. Cora E. Lewis of the University of Alabama at Birmingham
“This larger picture includes important relationships between BMI and other health outcomes, such as cardiovascular disease and its risk factors. Arguably, the most important relationship among the cardiovascular disease risk factors is diabetes, which is significantly more common in overweight than in normal-weight people.”
Considering the increasing number of children who are overweight, health experts are urging researchers and clinicians alike to act now and conduct research that goes beyond just BMI.
Dr. Lewis continues
“Weight gain is progressive and weight loss difficult. Although a young child is unlikely to have a heart attack, overweight children are likely to become overweight or obese adults, which puts them at risk for cardiovascular events as they mature. Achieving and maintaining a healthy body weight is of high importance for all Americans.”