If you consider yourself unhealthy just because your Body Mass Index (BMI) classification puts you in the overweight category, think again.
US experts are advising clinicians, health policy makers and weight watching individuals not to rely on the popular index to determine levels of health.
A study published in the International Journal of Obesity this week estimates that around 75 million US adults may be misclassified as “cardiometabolically” healthy or unhealthy when using the BMI.
About a quarter of 40,400 adults involved in the study were classed as obese or very obese, despite having a healthy heart and metabolism.
At the other end of the spectrum, around one third of people with a normal BMI fared poorly in cardiac and metabolic health tests.
Around one third of people with a normal BMI fared poorly in cardiac and metabolic health tests.
The paper’s authors write that it would be a “misuse of time, patient effort, and resources” for a doctor to prescribe weight loss to a healthy adult just because they are overweight, as per the BMI.
They add, “When healthcare providers deem these individuals as ‘healthy’ merely because they are not overweight or obese, critical diagnoses could be delayed or missed altogether”.
BMI is a measure of body fat based on height and weight. Overweight BMIs include calculations between 25 and 29.9, while people who have a score of 30 or over are classified as obese.
The authors also suggest that a misleading health diagnosis could lead to stigma and impact self-esteem.
“BMI may be seen as a quick, convenient, and inexpensive marker of health in the clinical setting,” they write. “Yet excessive focus on weight is likely to have detrimental consequences for the health and wellbeing of heavier individuals and thus should not be the principal outcome in health promotion efforts.”
Sydney-based clinical exercise physiologist, Dr BillSukala, says the findings are significant for Australians because “they underscore facts that clinicians in the trenches have known for a long time: that BMI should not be relied upon as a sole indicator of health”.
“Australia has a very high obesity rate just as in the United States and we need to take action towards reducing the incidence and prevalence of obesity here at home,” Dr Sukala explains.
“But using BMI as an indicator of overall health status without taking into consideration other biomarkers could be considered an inaccurate carpet bombing approach to measuring health.”
BMI does not factor in body composition – how much fat, muscle, and bone you have.
So people with a very high amount of muscle could register as ‘overweight’ or ‘obese’ on the BMI charts when in fact they are low or normal in body fat and not at risk for any cardiometabolic disease.
Using BMI as an indicator of overall health status without taking into consideration other biomarkers could be considered an inaccurate carpet bombing approach to measuring health.
“On the other hand, it is possible to have low muscle mass and an average amount of fat and yet still have a so-called "normal" BMI.
“If that fat is localised to the abdominal region (visceral fat), then this person of ‘normal’ BMI could, in fact, still be at risk for health problems.”
However, Dr Sukala adds, BMI offers great value as a population index, suited for public health research if used to examine the overall health of a large group of people. But he stresses it should not be used alone to determine an individual’s health status.
The US authors instead recommend that blood pressure, triglyceride, cholesterol, glucose, insulin resistance, and C-reactive protein data be used to measure health with or instead of BMI.
“I think Australians need to understand that BMI is only one small piece of the overall health puzzle,” Dr Sukala says.
“Go to your doctor and have a routine medical examination. Get a snapshot of where your health is today and then monitor it over time.
“…You don't want to get yourself worked up over your BMI unless your doctor has confirmed you have other health conditions.”