New Policy on BMI Use Will Change How Physicians Approach Diagnoses and CareJuly 13, 20234 min read
The Body Mass Index – or BMI – table was created in the mid-1800s, and for the last several decades has been viewed as the choice tool to diagnose obesity. However, the American Medical Association (AMA) recently issued a policy clarifying the role of BMI after taking a comprehensive look at both its benefits and limitations as a diagnostic tool.
In short, the new policy urges physicians to use BMI only in conjunction with other measures of risk and recognizes the historical shortcomings of the oft-used formula.
Lisa Diewald, MS, RDN, LDN, is the program manager of the MacDonald Center for Nutrition Education and Research with Villanova’s M. Louise Fitzpatrick College of Nursing. She applauds the AMA for embracing a more holistic approach to weight and health in individuals.
“This is a huge step forward and I think it will ultimately lead to better health care and an improved practitioner-patient relationship,” Diewald said.
To understand why, one must first understand the history of BMI’s use. The formula that spits out the number we have all come to understand as our BMI considers a person’s height and weight. It was developed in the mid-19th century by a Belgian sociologist to measure the socially ideal person. The modern term and application came about in the 1972 and has been a routine measurement ever since because it is easy, fast, costs nothing and in some cases, said Diewald, does correlate with body fat.
But in recent years, large scale studies have exposed some of the limitations of the measure, building to the point where they needed to be weighed against the overt benefits. For starters, BMI does not measure body fat – or adiposity – directly. Adiposity, per Diewald, is more closely associated with health risk than BMI.
“For this reason, health risk for some individuals with normal BMI but high body fat has been underestimated, and some with high BMI but normal body fat levels have been overestimated,” she said.
Nor does it “differentiate between muscle, bone and body fat, or distribution of fat on the body,” Diewald said. “We know that all these factors can influence health and chronic disease risk.”
Other comorbidities or chronic conditions that wouldn’t show up on a BMI chart alongside a number in the “normal” range can also impact health. Conversely, there are health conditions that might be incorrectly assumed just because a BMI is high.
“Not every person with a high BMI experiences these chronic conditions, so developing a more holistic approach can lead to better assessment, treatment and outcomes,” Diewald said.
Another shortfall she pointed out was its failure to factor in gender, race, body composition, ethnicity or physical activity level. Think back to the origins of the chart, intended to be a social standard created in Europe nearly two hundred years ago.
“BMI tables were originally designed in the 1800’s using a population of white men,” Diewald said. “Understandably, at one point in time it was all we had to evaluate weight status, but it may not be accurate to use this standard alone with all groups of people.”
These societal, gender and racial/ethnic factors led the AMA to explicitly cite “historical harm, use for racist exclusion and because BMI is based primarily on data collected from previous generations of non-Hispanic white populations” in the new policy on its clinical use. Additionally, the policy addressed the differences in body composition across genders, races and ages that were not being considered.
There is also an ignored mental component in its use to diagnose obesity, which can lead to avoidance of doctor visits and, in turn, further physical issues.
“Obesity is a multifactorial, complex condition and addressing it with individuals needs to be done with empathy and sensitivity, beginning with how it is measured,” Diewald said. “There are numerous factors influencing weight well beyond simply food intake, physical activity level and BMI, so it is important for practitioners to recognize that and communicate this to patients.
“It is extremely difficult for people with higher weight to be told that they have a high BMI and simply need to eat less and move more. When BMI is used as the sole indicator of weight status, this can be psychologically damaging. We know that many who have been told to lose weight simply based on a high BMI may avoid going to the doctors for routine medical visits and skip necessary preventive care.”
It will not be easy, she said, to move away from a method used for so long that has been ingrained as a part of a routine medical visit, but Diewald thinks utilization of the tool in conjunction with other assessments is the best way put this new policy to practice.
She advocates for measures such as “Using BMI as only one of several indicators of chronic disease risk, asking permission to discuss weight and health risk, [and] using shared decision-making between practitioners and patient to determine course of treatment.”
Education is also paramount to proper assessment of weight-related health risks.
“Education cannot stop with physicians, however,” she said. “I think this provides an excellent launching pad for enhanced collaboration among health professionals such as dietitians, nurses, nurse practitioners, physician’s assistants and others involved in providing care, nutrition counseling and lifestyle modification support to patients… Doing this can better fine tune recommendations for treatment, leading to improved outcomes.”
Lisa Diewald Program Manager, MacDonald Center for Nutrition Education and Research | M. Louise Fitzpatrick College of Nursing
Lisa K. Diewald, MS, RD, LDN, is an expert in healthy eating and nutrition education programs for children and adults