Should we be saying bye to BMI?
What is BMI?
In 1832, Adolphe Quetelet, a mathematician, created “the Quetelet-Index” as a way to measure body weight in different populations.
A physiologist named Ancel Keys brought back Adolphe’s calculation in 1972 and named it the Body Mass Index (BMI). Despite acknowledgement from Quetelet that it was a population-based tool, not meant for individuals, BMI has been widely adopted by the medical world ever since, as a way to categorise individuals into ‘healthy’ or ‘unhealthy’ camps. As if it were as black and white as that?!
BMI is measured by dividing an individual’s weight by their height in metres squared. This generates a BMI score and places individuals into different weight categories.
If your BMI score falls out of the “normal” range, it is considered to be “less healthy” *rolls eyes*. As though “health” depends on an ideal body size with little regard for other factors including behaviours and measures including bloods and vital signs like blood pressure and heart rate. BMI is part and parcel of a range of factors which fuels the global obsession there is with weight and the “need” to lose weight in order to achieve optimal "health”. This can lead to further stigmatisation of larger bodies, especially in health care settings.
Why we need to stop using BMI as a proxy for health
BMI is not a good measure of “health” and wellbeing because it doesn’t take into consideration the overall picture of an individual e.g. health endorsing behaviours, bloods and other markers of wellbeing. Usually, it is much cheaper and easier to have someone jump on the scales than to consider the complexities of their health history and explore further texting. As such, BMI is popular, but it means we may all be losing out.
An individual’s body weight does not directly correlate to their health (1). BMI doesn’t account for the body composition of an individual, for example, body fat percentage compared to lean muscle mass. This often means that muscular people, including athletes, are often classified in the “overweight” or “ob*se” BMI categories despite usually being metabolically fit. Equally, studies have shown that you can be metabolically fit and fat which means individuals in the “overweight” or “ob*se” BMI categories may also be wrongly stereotyped as “unhealthy” (8).
BMI takes the focus away from important modifiable lifestyle behaviours such as the importance of having adequate sleep, nutritional intake, movement and physical activity, stress levels, smoking, and alcohol intake (2, 3). BMI also fails to consider an individual’s relationship with food, how flexible they are with their intake and variety, or what they are actually eating and how much/often. Without this important information, many health professionals are left to assume answers to these questions or to completely ignore them altogether. This can leave people with actual medical conditions and needs to go undiagnosed and unnoticed. For example, an individual with a “normal” BMI, may have health conditions overlooked because they look “normal”. Equally, individuals in larger body’s may be told to lose weight without proper medical investigations for their symptoms. In eating disorders, individuals who don’t fall below a certain BMI threshold may be overlooked and turned away from treatment despite repeated disordered eating behaviours that impact on health and quality of life. This is problematic.
Those with a higher BMI experience more discrimination
There is a largely unchallenged and accepted perspective from healthcare providers viewing ob*sity as an avoidable risk factor. This may lead many healthcare providers to feel less pressure to behave in a non-prejudicial way towards those with higher BMIs (4). Many doctors and healthcare professionals feel an obligation to discuss a patient’s weight without their permission, before addressing what they may have come in for which has the potential to cause intended harms. For example, there are numerous accounts from women who had their health concerns dismissed and were told to lose weight to later find out they had cancer. This desire to intervene at the sight of ob*sity can lead to over-attributing symptoms and problems to an individual’s weight without considering further diagnostic testing or treatment options besides weight loss (5).
However, achieving a “normal” BMI via a lifestyle weight loss practice is not as effective as it is made out to be. In 2015, a cohort study reviewing health records of 176,495+ individuals with a BMI >30, over a 9 year period, looked at the probability of these individuals attaining a “normal” BMI. Unsurprisingly they found that women with a BMI of >30 had an annual probability of 1 in 124 for attaining “normal” BMI and men had a 1 in 210 annual probability (6). From this study, we can conclude that such weight loss interventions are ineffective for the overwhelming majority of people. In contrast, studies do support that individuals can improve their “health” and wellbeing regardless of changes in BMI through engaging in health-promoting behaviours. For example, one study found that individuals in higher BMI categories who don’t smoke, drink within the guidelines, eat 5 portions of fruit and veg a day and engage in regular physical activity have been shown to have a similar mortality risk as those who are of a ‘normal’ weight and also engage in those health-promoting behaviours (9).
Is BMI racist?
To create his “Quetelet Index”, Adolphe used data from predominantly white European men. Findings from this white male-dominant study population have been used and extrapolated to create ‘norms’ and expectations for body size for the diverse people of the world. This is wrong! When we look at the history of body standards we find that the “thin-ideal” internalisation was used to support white superiority. The BMI used today has inherited much of that racism with its categories of “underweight”, “normal”, “overweight” and “ob*ese”, and what those look like, putting emphasis on the need to reach the “normal” BMI category and looking at the “overweight” and “ob*ese” BMI categories as inferior (7).
BMI may be helpful in certain health care settings, but it is a flawed-tool on which to base someone’s overall “health”. However, it is so widely accepted and used by healthcare professionals for this purpose. BMI score really doesn’t tell the whole health story and disregards the wellbeing of individuals and diversity amongst different races and ethnicities. A single number really cannot determine how healthy an individual is overall!
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