Why is the BMI flawed and misleading

When it comes to our health, it's easy to get fixated over numbers: counting steps, miles, calories burnt, hours of sleep and more. The health care system often promotes this emphasis on numbers, since it relies on various formulas and values to evaluate aspects of our health.

Body Mass Index (BMI) is one such tool used which was created in the 19th century and has been used widely since 1970’s. Many health care professionals (HCP’s) globally criticize the use of BMI and here’s why.

BMI Background 

BMI is a diagnostic tool developed by Adolphe Quetelet who was a mathematician, astrologer, and statistician. He concluded the tool is used as a measurement of a person’s weight with respect to square of their height and called it the Quetelet’s index. It was created with Belgians in mind and does not necessarily apply to most populations. Since 1972 WHO has used this tool at a population level to measure a populations health status and address obesity related public health issues. However, currently many HCP’S, fitness and health coaches heavily rely on BMI to determine an individual’s health, categorizing them as underweight, normal, overweight, or obese. The way we are using BMI can end up doing more harm than good to people.

BMI does not consider your body composition, shape and much more.

BMI fails to provide actual information on body composition like amount of muscle, bone, fat, and other tissues, (it does not distinguish between lean mass and fat mass). It's an indirect measure of body fat that doesn't take into account important details about age, sex, ethnicity, bone structure, and fat distribution. For example an elderly person may have a high BMI and may be asked to lose weight which could put them at a risk of losing muscle which is already lower due to age. Furthermore, many athletes often get classified as “overweight” only because they are more muscular – not very reliable, is it?

Overweight, obese and being unhealthy

Time and time again we fail to understand that just because the BMI classifies a person as being “overweight” or “obese,” it doesn’t directly mean an individual is unhealthy. It is so common in our culture to place so much emphasis on being thin and be categorized as “normal” weight. Most of the time when an overweight person visits a doctor, their weight is diagnosed as the issue and they are asked to start losing weight, without even considering further treatments or tests. This has led to many mistreatments, worsening the patient’s condition both physically and mentally. This misclassification of health based on BMI can really harmful and yet, we still continue to rely on this one tool.

BMI and South Asian population

The cut-off points are different for South Asians and Europeans; for South Asians it is lower as they are found to be more at risk of the problems of developing type 2 diabetes and heart disease. Even though WHO has recommended Asian populations to start using these in practice, we haven’t seen a change in international BMI cut-off points. More research is required to have substantial data to have accurate calculations within populations as Taiwanese people may have even lower cut off points compared to the rest. Lastly, BMI does not consider where the fat is stored; Asians tend to store more fat around their organs (visceral). You could still be in the “healthy / normal” range and be storing fat around your vital organs such as liver or heart. 

What next?

BMI is ONE of the tools that should be used to assess health risks as its cheap and is required for population based data. Other factors such as blood pressure, cholesterol level, blood sugar level, family history of heart disease, age, gender, waist circumference, skin fold thickness, level of physical activity, menopause status, smoking status, etc. should also be taken into consideration while assessing health risk. The biggest issue we face is the importance we place on weight itself rather than focusing on health. We need to provide medical care for people of all sizes and stop using weight loss as the primary solution. We are not only discriminating people living with overweight / obesity, but we are also pushing them away from getting the right treatment.