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The body mass index or BMI predates the bathroom scale by more than half a century, but it has not changed with the times. The BMI was created in the 1830s before calculators and computers existed. It was a simple system to measure body fat based on a person's height and weight. However, in recent decades, many medical professionals have acknowledged the BMI's flawed history.
"The numbers have historically excluded patients with different ethnic and racial backgrounds since it was created to measure the 'normal' weight for a white population," said Juliana Simonetti, MD, co-director of the Comprehensive Weight Management Program at University of Utah Health. Simonetti welcomed the American Medical Association's (AMA) vote this summer to adopt a new policy that encourages doctors to de-emphasize their reliance on BMI when assessing individual patients' weight and health.
"This is a great step forward in identifying and helping healthcare providers to effectively treat patients with obesity in a more targeted and individualized way. We can still use BMI as a screening tool, but it is important to understand its limitations and use additional measures and tools such as body composition to evaluate patients for obesity-related conditions and complications," Simonetti said.
At the clinic where Simonetti practices, she emphasized that they already use a variety of tools to assess how a patient's weight may be affecting their overall health. "It is important to take into account the patient's waist circumference, glucose levels, cholesterol measurements, liver function, blood pressure, etc. We now also have fancier scales that help measure bone vs. muscle vs. body water (fluid) which gives us other measures to look at."
A well-recognized flaw of the BMI is its inability to focus on gender and age. Simonetti suggested that "a higher BMI may underestimate muscle mass in a younger athlete and overestimate muscle in an elderly person who may have less muscle and more fat mass. This is something I often worry about and talk to many of my older patients about as they are working on weight loss."
Simonetti added there are always new concerns that arise as the science of weight control evolves. She said, "In particular, new medications such as Semaglutide and tirzepatide, can lead to more substantial weight loss, which is associated with loss of muscle mass. That, in turn, can contribute to the risk of sarcopenia, muscle weakness, and falls which are especially concerning for the elderly." At the weight management clinic, Simonetti said they often discuss the need for appropriate protein intake and resistance training to help maintain muscle mass.
Along with the release of its new policy on the use of BMI data, the American Medical Association recognized the metric's historic use "for racist exclusion." Simonetti said this assessment captures some long-held concerns about the BMI within medical communities who treat diverse patient populations.
"Research has demonstrated that BMI does not appropriately capture the health risks associated with obesity in diverse ethnic populations. Individuals from certain backgrounds, such as Asian, African, and Hispanic populations, may have a higher percentage of body fat or different fat distribution patterns at lower BMI values compared to individuals of European descent. This means that these individuals may have increased risks of metabolic disorders, cardiovascular diseases, and other obesity-related health conditions at a lower BMI," said Simonetti.
Even as the BMI has virtually stood still in time, other tests and measurements designed to assess the impacts of a person's weight on their overall health are quickly being developed and put into practice. The genetics of weight gain and loss is one important example of a relatively new science that can give patients a better understanding of why their BMI indicates they have obesity.
"We now know that obesity is a highly inheritable disease with some studies suggesting that the heritability of obesity is around 60-70%. This means the way our bodies accumulate weight and store fat is passed down from generation to generation," said Simonetti. The doctor added that "We know that there are genetic mutations that further contribute to weight gain."
Further exploration of a patient's genetics is already playing a role in diagnosis and treatment at the U of U Health Weight Management clinic. Simonetti said, "We offer genetic testing which focuses on an obesity panel looking at 79 genes that are associated with obesity for patients who have a history of childhood excess weight/obesity and those who present with hyperphagia (insatiable hunger, lack of satiety)."
Simonetti highlighted some important research discoveries. "We found a larger number than previously expected of patients with certain mutations that impact appetite control and metabolism. These mutations can cause an error message from the gut and fat storage to the brain. The brain thinks the body is starving, even when someone has enough food and energy stored in fat cells. This can cause insatiable hunger and the slowing of their metabolism, resulting in significant weight gain and obesity."
The AMA's decision to de-emphasize the use of the BMI has been called "timely and necessary." It should help to ensure more Americans battling weight issues can access the cutting-edge diagnostic services and treatment being offered at programs like the one at University of Utah Health.
