5 Reasons Why BMI is BS


By Nikki Kang

For as long as most of us can remember, a doctor’s visit almost always included a discussion on the magical number which supposedly defines your overall health status. Known as the BMI, or body mass index (or what we prefer: the BS Measuring Index!) the BMI is used to measure body fat (although quite inaccurate and we uncover why). Once the BMI is obtained, it then categories someone as  “underweight,” “normal weight,” “overweight,” or “obese”. Typically, these ranges are then further used to evaluate one’s disease risk. While the BMI has limited use in research, it has absolutely NO place in assigning or predicting health for the individual. So how did this number become a measurement as commonly used as a stethoscope or blood pressure cuff in healthcare? 

Brief history: The first version of the BMI was created in the 19th century and was actually called the Quetelet index. It was created by Lamber Adolph Jacque Quetelet, a Belgian astronomer. Quetelet created this index to develop “social averages” so he could then gather the characteristics of the “average man”. Thus the Quetelet index was not created for use as a health indicator but rather for gathering population data. It was later in 1972, when the Quetelet index was reinvented to become the body mass index, by Ancel Keys. Keys reused Quetelet’s index to argue the validity of MetLife Insurance’s data tables on desirable weight, based on height. His use of the BMI was solely in population based studies, and not for diagnostic purposes. During this time, Keys had also pointed out that BMI does not accurately reflect percentage of body fat. At some point, this advice was ignored, and has now continued to be used as a measurement of body fat. 

Fast forward to the 21st century where preoccupation with weight has surged due to the emphasis placed on one’s BMI, leading people to believe that they are “overweight” or “obese”. But the fact is there are so many misconceptions about the BMI and in reality, the numbers are super arbitrary. The obsession with BMI has led to an increase and fascination in weight loss programs, diets, drinks, and books; The only people that seem to be benefiting from these weight loss products is the industry which is supplying them. Those investing in these products find themselves facing a number of other consequences that come along with dieting, such as fixation with food and their body, weight cycling, eating disorders, decreased self-esteem, and many other issues which can disrupt mental health and wellbeing. 

As the consequences of dieting seem to be increasing, one may question whether or not there is more harm being done than good. This question has been asked, and has led researchers to also challenge the validity of the BMI.  What was found was that the BMI is not as accurate of a health indicator as we have all been made to believe, and here are 5 reasons why its total BS: 

1. BMI does not differentiate between lean body mass, body fat, muscle, tissue or fluid.

The BMI is used to determine body fat mass. However, when calculated, lean body mass vs body fat mass cannot be differentiated. In order to really differentiate between the two, you would need a fancy X-ray called a DEXA scan, which is costly and honestly unnecessary. Therefore, an individual can have a higher BMI, but it may be due to lean body mass rather than body fat mass (which is typically what is associated with disease risk). 

2. A BMI doesn’t tell you how “healthy” you are. It doesn't take into consideration body composition or health behaviors. 

Those with a “normal” BMI may have underlying health issues and might not be aware because they are considered to have a “healthy” BMI (weight biases like this are harmful and affect people of all sizes). There are so many other factors which contribute to an individual’s overall health status and are typically ignored in the presence of a low or high BMI. If someone with a “normal” BMI finds themselves with high blood pressure or high blood sugar, they can technically be considered as “unhealthy”, because these factors put them at higher risk for chronic diseases, not their BMI. This is true for both ends of the spectrum, where someone with a higher BMI may be perfectly healthy according to their labs. This is why it’s essential for practitioners to assess an individual’s bloodwork, whether or not they are engaging in joyful movement, and if they are well nourished.  Some may argue that BMI is a quick way to (supposedly) assess modifiable behaviors but you know what’s also a quick and more accurate way to assess modifiable behaviors? Asking if someone is eating a variety of fruits/vegetables, if they drink alcohol or smoke, or engaging in physical activity. Can you imagine what a visit to the doctor’s office would be like if medical providers encouraged these changes rather than focusing on weight? 

3. BMI alone is not an accurate indicator for morbidity/mortality rate. 

In most studies, BMI is used to assess morbidity/mortality risk. However other factors are almost always ignored. These other factors which can play a role in morbidity/mortality rate include family history of disease, smoking, alcohol consumption/abuse, exercise, mental disorders, and history of dieting. When it comes to identifying the “obesity” weight ranges, studies also fail to identify at what point in the life cycle has the weight gained and the rate at which the weight is accumulating. Moreover, fat is not a disease. Bodies exist in all shapes and sizes. By assigning a disease (e.g. obesity) to a body size, even when the individual is eating well, has great bloodwork and engaging in joyful movement - this is dehumanizing and promotes weight stigma.  

4. Increased BMI in children is expected due to puberty.

While the BMI measurements for children take their age into account, it is still not an accurate indicator of health. This is because during and after puberty, both males and females acquire changes to their bodies, which allow for an increase in BMI. When girls go through puberty they must gain a minimum of at least 10% body fat in order to get their first period, whereas when boys go through puberty, they tend to gain weight slowly over the years. The BMI misses these nuances. These are normal changes expected to occur during adolescence, and are not reflective of poor health. 

5. A low BMI does not increase longevity. 

Another common misconception is that a lower BMI equates to living a longer life. However, many studies have shown that those who are “overweight” or “obese” actually have greater longevity than those who are of normal weight. One study has even concluded that obesity is not a notable risk factor for mortality, especially when socioeconomic status and other risk factors are controlled for. 


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