Is BMI the best metric for assessing obesity and cardiometabolic risks?
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BMI is a good metric, but cutoff values for cardiometabolic risk can change based on an individual’s profile.
Obesity is a dysregulation of the energy balance pathways in the human body. People with obesity are defending an abnormal body weight set point, and we can recognize and start to address that with the easiest tool we have, BMI. You just need height and weight, and you can calculate it. However, in certain populations, the standard cutoff values do not accurately correspond to risks. Someone who is Asian and has a BMI of 23 kg/m2 or 24 kg/m2, may have a “normal” BMI, but in reality, patients of Asian descent have a higher risk at a lower BMI. It’s the same thing for African Americans at higher BMI cutoff values.
At the same BMI, someone aged 75 years has a different risk than someone aged 17 years. As adults get older, they present with more sarcopenic obesity, less muscle mass, visceral adiposity and loss of fat in different areas. BMI may not be reflective of risk for them.
Male adolescent athletes have a higher proportion of muscle mass, especially when there are growth hormones and other factors contributing to their physiology, growth and development. They may have a high BMI, but when you do the body composition analysis, they may have a very high muscle mass compared with body fat. That’s important to take into consideration as well.
BMI is not 100% accurate for determining cardiometabolic risk. It’s a good indicator if it is coupled with medical judgment and decision-making.
- For more information:
- Gitanjali Srivastava, MD, FACP, FAAP, is associate professor of medicine, pediatrics and surgery, director and chief of clinical obesity medicine, program director of the obesity medicine fellowship and co-director of the Vanderbilt Weight Loss Center and Vanderbilt University Medical Center.
BMI is best used as a screening tool, followed by a more in-depth assessment to assess cardiometabolic risk.
BMI is a good screening tool because it is quick, easy to calculate, and you don’t need specialized equipment. It’s something that every primary care doctor, specialists and patients can do. We have good, standardized data showing that among large populations, BMI is highly correlated with cardiometabolic risks. However, that correlation is only for large populations.
When you look at individuals, there is a wide range of outcomes for any given person’s BMI. That’s why we need to go beyond BMI when we’re working with a patient to understand what their risk is and what intensity of treatment we want to consider.
There are markers that are more precise than BMI, but they take more resources and do not add enough clinical value to support their use. We can certainly improve on BMI by instead doing an underwater body densitometry test. We’ll know exactly what a patient’s body composition is and will have a much better assessment of their risk. The problem is that test is the exact opposite of BMI. While it’s very accurate, it’s incredibly expensive, it’s very difficult to get a machine, and it takes up the provider’s time. For many patients, it doesn’t give us any additional useful information.
The way to improve on BMI is to use it for what it is: a quick screening tool. Then, as needed, you can take the next step and do a more in-depth test to better stratify the patient’s risk stratify. We need to treat patients in an individualized way, not in a formulaic way.
- For more information:
- Scott Kahan, MD, MPH, is the director of the National Center for Weight and Wellness, a faculty member of the Johns Hopkins Bloomberg School of Public Health and an Endocrine Today Editorial Board Member.
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