We’ve all stood in front of a mirror, trying on new clothes, wondering whether the polo is too tight or if we’ve gained a few pounds over the winter. It’s natural. It happens to all of us—unless your name is Glenn Powell or Scarlett Johansson and you have a team of nutritionists, personal trainers, and the kind of genetics that seem to make every photo picture-perfect.

“Is my blood pressure high because of my weight?” people often ask me, hoping for a clear answer about their health.

As a cardiologist, I get this question a lot: “Is my [insert disease] because of my weight?” My patients’ eyes lock onto mine, searching for any hint of a flinch or hesitation in my response. The truth is, it’s challenging to be honest with just one word or a single measurement. There’s a gray area between what society has historically labeled as “fat,” “chubby,” “thin,” or “too thin,” and health is far more complex than fitting into these categories.

For the longest time, physicians have relied on the Body Mass Index (BMI) to help answer that question. The formula is simple—just basic iPhone calculator math. You plug in weight divided by height squared, and voilà, your BMI is revealed.

But BMI doesn't tell the whole story. Take a young, muscular Notre Dame linebacker, for example. His BMI might be classified as obese, despite being purely lean and ripped, simply because BMI doesn’t differentiate between muscle and fat.

Over time, more data has poured in, and as scientists, we’ve come to realize that BMI isn’t as straightforward as we once thought. Sure, countless studies indicate that BMI ranges outside “normal” are associated with worse health outcomes, including higher risks of heart disease and death. But that’s only part of the story. For instance, not everyone classified as morbidly obese develops heart disease, high blood pressure, or diabetes. However, if you already have one of these conditions, being obese often worsens the outlook. So, it begs the question: Is being labeled “fat” by your BMI the best way to measure health risks? Is BMI just half telling you the truth?

Enter the Body Roundness Index (BRI). Unlike BMI, BRI considers body composition, specifically the amount of visceral fat inside your abdomen. Spoiler: BRI is much harder to calculate than BMI. Think TI-89 calculators from college: 364.2 − 365.5 × √(1 − [waist circumference in centimeters / 2π]² / [0.5 × height in centimeters]²). 

Okay, I know that looks complicated, but don’t worry—there are plenty of free online calculators where you can plug in your height and waist circumference (measured around your abdomen, at the level of your belly button). Besides, you’re not expected to do this math alone. Your primary care provider can help answer any questions.

As a whole, BRI offers valuable insight into whether you have too much fat in your abdominal cavity, and it’s quickly becoming one of the most important indicators for predicting medical complications.

Studies strongly suggest that BRI outperforms BMI and other measurements in predicting risks for kidney disease, metabolic issues, cancer, cardiovascular disease, and even all-cause mortality. As it stands, we should be talking more about BRI than BMI to judge people’s health and risk factors. 

So, the next time you talk to your doctor, don’t just ask how "fat" your BMI is—ask about your abdominal fat and Body Round Index, too. Both your BMI and waist size are important when discussing your overall health.