At most medical checkups, patients step on a scale to measure their current weight. Physicians then often use this number to calculate the patient's body mass index (BMI), a commonly used indicator of overall health. This measurement is especially relevant when considering eligibility for GLP-1 weight loss drugs such as Ozempic or Wegovy. But how accurate is BMI as a health indicator?
Randall Sisam, DO, assistant professor of clinical medicine and director of primary care skills at PCOM South Georgia, regularly teaches medical students about the uses—and limitations—of BMI.
“It's essentially a measurement of someone's height and weight,” Dr. Sisam explained. “What it tries to do is assess people who weigh more in relation to their height, as they might tend to have more health issues. Obviously, you can't compare the weight of someone who's 5-foot-2 to someone who's 6-foot-2 or 7-foot-2. They're going to weigh differently for different reasons. So BMI was developed as a way to associate weight with height in a standardized way.”
This ratio of height to weight falls into several categories.
“There are ranges of BMI based on height and weight that go from underweight to healthy weight to overweight and obese,” Dr. Sisam said. “Obesity itself is further divided into three classifications. BMI helps us categorize a person’s weight relative to their height.”
In primary care, BMI is often used as a quick screening tool to determine whether a patient is within a healthy weight range.
“It can be useful if you're trying to quickly assess whether someone is at a healthy weight,” he said. “It's not as helpful when someone has a high volume of muscle mass.”
He used athletes as an example.
“You have to consider people with higher muscle mass,” Dr. Sisam said. “Muscle weighs more than fat. Athletes might have a BMI that classifies them as overweight or even obese, but when you actually assess their body fat percentage, they're often in excellent health.”
In these cases, there are alternative tools to assess body composition more accurately. For example, skinfold calipers can estimate subcutaneous fat by measuring the thickness of skin folds. However, he pointed out that the more concerning type of fat is actually visceral fat, which surrounds internal organs.
“Visceral fat is more worrisome because it's more strongly associated with health
risks,” he said. “Fat in and around the lungs, heart, or within the abdominal cavity
can be much more damaging than subcutaneous fat—the fat just beneath the skin, the
kind you can ‘pinch an inch’ of.”
Measuring visceral fat, however, typically requires advanced imaging like MRI or methods
such as bioelectrical impedance analysis. Because these methods are more complex and
less accessible, BMI remains a simple, though imperfect, guideline.
In 2019, Philadelphia College of Osteopathic Medicine (PCOM), a premier osteopathic medical school established in 1899, extended its commitment to the Southeast by establishing PCOM South Georgia. An additional teaching location in Moultrie, Georgia, PCOM South Georgia offers both a full, four-year medical program leading to the Doctor of Osteopathic Medicine (DO) degree and a Master of Science in Biomedical Sciences. PCOM is a private, not-for-profit institution that trains professionals in the health and behavioral sciences fields. Joining PCOM Georgia in Suwanee in helping to meet the healthcare needs of the state, PCOM South Georgia focuses on educating physicians for the region. For more information, visit pcom.edu or call 229-668-3110.
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