Body mass index, or BMI, has long been the standard for measuring health. The simple formula is widely used to classify whether our weight falls within a “healthy” range for our height. BMI provides an estimate of a person’s overall risk of disease and is used worldwide to measure obesity.
But BMI has been criticized because it can be inaccurate in estimating body fat and does not provide a complete picture of a person’s health. Research also shows that relying only on BMI to predict a person’s risk of health problems can be misleading.
The formula for calculating BMI was first invented in 1832 by the Belgian mathematician and astronomer Adolphe Quetelet. To calculate it, divide the weight in kilograms by the height in square meters (kg / m2). In adults, BMI is classified as follows:
Sarah Sauchelli Toran and Karen Coulman, Author provided
BMI is a fast, easy, and inexpensive way to diagnose overweight or obesity that only needs a measurement of weight and height. Since obesity carries an increased risk of disease, including heart disease, stroke, and diabetes, BMI can identify people at increased risk of developing health problems. It is also sometimes used to make decisions about who receives certain treatments and to assess how effective certain weight loss interventions are.
But BMI alone does not give a complete picture of a person’s health risk, as it is simply a measure of body size, not disease or health. BMI does not actually measure body fat, a key element when establishing a health risk. Although it provides a rough indication of body fat, it does not distinguish between weight from fat and muscle.
High-performance athletes, such as rugby players or sprinters, would be classified as “overweight” or “obese” by their BMI due to their increased muscle mass. Looking at just BMI would give the impression that athletes are at a similar risk of having the same health problems as an overweight person, despite research showing that active people have better cholesterol, blood pressure, and lower levels. of blood sugar than someone who is inactive.
The BMI also doesn’t tell us anything about where body fat is distributed. Body fat stored around the abdomen (a form of “apple”) presents a greater health risk than body fat stored around the hips. This form of “apple” is associated with an increased chance of developing metabolic syndrome. This is a combination of related conditions, such as high blood pressure, high glucose, and high cholesterol levels, that increase the risk of heart disease, stroke, and type 2 diabetes.
BMI categories are also somewhat arbitrary. A study of 13,601 adults showed that the prevalence of obesity was much lower when defining obesity using BMI instead of body fat percentage. Using the BMI categories, fewer people were found to be obese, although many would have been diagnosed as such due to their percentage of body fat.
These categories may be even less accurate in predicting health risks in people from ethnic minorities and older groups. For example, Asian people have a higher risk of developing type 2 diabetes and heart disease with a lower BMI than Caucasian people. This may be due to a higher percentage of body fat with similar BMIs, and / or a greater tendency to store fat around the abdomen.
Research also shows that in adults older than 65, having a BMI in the “overweight” category was not associated with an increased risk of death, while a BMI below 23 was. Therefore, the normal ranges may not work well to predict health risks in older people.
People may also have a “normal” BMI, but they are at increased risk for heart disease and type 2 diabetes, depending on factors such as blood pressure or body fat distribution. Measuring waist circumference and body fat percentage can be more helpful in such cases.
Reliable, affordable and accurate indicators of health status are important. BMI is easy to measure and provides a rough estimate of disease risk. But while it’s a good starting point, BMI should be used in conjunction with other measurements to get a fuller picture of a person’s unique health risk. Lifestyle factors (such as smoking, physical activity, diet, and stress levels) and blood pressure, blood sugar, and blood cholesterol levels should be considered in conjunction with BMI to establish the health risk.
Athitat Shinagowin / Shutterstock
Waist measurements (such as waist circumference and waist-hip ratio) can estimate abdominal body fat, but can be difficult to perform and less accurate in people with a BMI greater than 35. Tools that break down body composition such as bioelectric impedance analysis and dual energy X-ray absorptiometry: they work better. But these can be very expensive, long and complex to use, and would not be practical for GPs to use daily.
Staging tools can provide a more personalized assessment of the risk to health and early death in people living with obesity. These are scoring systems that take into account metabolic, physical, and psychological health to rank health risk. They are designed to be used in conjunction with BMI to identify people who would most benefit from weight management interventions.
Although BMI provides a convenient and simple tool to understand the risk of disease, it does not provide a complete or totally accurate image of everything that influences our health. Using other measurement tools in conjunction with BMI can provide a more complete picture of health and disease risk, and can also help guide decisions about the best health interventions for a specific person.
