BMI is Outdated
An example of a body composition analysis machine
What is BMI?
BMI, or body mass index, is a term that most people have heard. Whether it's something you heard at the doctor's office, saw on your medical chart, or calculated yourself online, most people have come across their BMI. This number has been used for decades to determine a person's health, but BMI has many shortcomings. Adolphe Quetelet, its inventor, never intended its use in medical practice. BMI was developed by Quetelet, in the 1830s to define the body type of the "average" person. It became popular as a screening tool for obesity in the 1990s because nothing better was available and continues to be used today, but its popularity is waning.
The Problems with BMI
First, the value is quite simplistic; it's a person's weight in kilograms divided by their height in meters squared. The utility of this was intended for large population-based studies. It is effective in that setting but correlates poorly to health determination amongst individuals.
Currently, medicine uses BMI to place an individual into categories: healthy weight, overweight, or having obesity. The intent of the value is to extrapolate the degree of excess fat mass and to predict a high risk of developing diabetes and metabolic syndrome. However, given the simplicity of the measurement, you can imagine how this value can be faulty.
BMI Classification Chart
Understanding Weight Categories According to the World Health Organization
Body Composition
BMI fails to account for body composition, which is the most critical factor in metabolic health. Individuals with "normal" BMI but with sarcopenia or little muscle mass and excess % body fat are not metabolically healthy. In contrast, athletes with large muscle mass may have an "overweight" BMI. Furthermore, the distribution of fat is critical in determining metabolic risk. Fat deposition is broadly categorized into subcutaneous, the fat below the skin we can see, or visceral, the fat deep in and around our organs we cannot see. Of the two types, visceral fat is far more dangerous. Subcutaneous fat may be protective depending on location. For example, fat around the hips and buttocks is protective against heart attacks, whereas fat around the upper body poses more risk.
Racial Disparity
Most BMI data is useful for white people. Asian populations have a risk of diabetes at a BMI of 27 or more due to a predisposition to developing visceral adiposity more readily and potentially have obesity at that measurement. Black individuals may remain metabolically healthy at a higher BMI than 30 due to more subcutaneous fat distribution than visceral adiposity.
Alternatives to BMI
Several alternatives to determining metabolic health include body measurements and lab work. Body composition analysis is an excellent tool when done accurately. While DEXA is the gold standard in practice, it does require a small amount of radiation to be performed, and some individuals may not be comfortable with that on a routine basis. Professional bioimpedance machines are comparable in accuracy and can give you a breakdown of your muscle mass, visceral fat, subcutaneous fat, and, depending on the quality of the machine, even muscle distribution. If you see us in the office, your body composition analysis via bioimpedance will be included in our visit. A low-cost and easy alternative way to measure your metabolic health is by taking a waist circumference. Although there are ethnic differences in metabolic risk at a given waist circumference, the data show that a waist greater than or equal to 35 inches in women and 40 inches in men is consistent with the disease of obesity. These cut-offs can be even lower in certain ethnic groups. An even better predictor is the waist-to-hip ratio, as individuals with more fat around their waist than hips are at a much higher risk for diabetes, cardiovascular disease, and liver dysfunction.
Why We Need to Move Away from BMI
BMI is used to decide which person is a candidate for medication intervention or surgery, but given that on an individual level, it is not a good predictor of metabolic health, that is not the correct strategy. Some obesity medicine programs will exclude patients who do not meet a BMI cut-off from receiving their help. This leaves a lot of patients needing more proper help. We are likely undertreating and potentially overtreating other patients when using BMI. As other metrics become more popular, it is essential to review your metabolic health with a healthcare provider that is well-versed in obesity medicine and metabolic disease. If you want to learn more, book a call with us today.