New research presented this weekend at the American College of Cardiology’s Annual Scientific Session may add more fuel to the fire concerning the reliability of body mass index (BMI) as a precise measure of health.

The study authors reanalyzed data they obtained from an earlier randomized trial of 200 Type 2 diabetes patients with relatively healthy hearts who were given intensive CT screening in hopes of preventing future heart disease. This time around, the researchers examined whether their patients’ waist circumference had any relationship to their risk of future heart disease. They did the same calculation for BMI as well as body weight. After controlling for all other factors, the authors found that waist circumference consistently served as a better predictor of heart function over the other two.

"This study confirms that having an apple-shaped body — or a high waist circumference — can lead to heart disease and that reducing your waist size can reduce your risks," said senior author Dr. Brent Muhlestein, a co-director of research at the Intermountain Medical Center Heart Institute in Salt Lake City, in a statement.

In an interview with Medical Daily, Muhlestein explained that his team, comprised of researchers from Intermountain as well as Johns Hopkins Hospital in Baltimore, was already well prepared to look at the connection.

“It has been proposed for some time that intra-abdominal fat may be more inflammatory and may contribute more to atherosclerosis progression than other forms of fat,” he said. “Therefore we measured abdominal circumference, which is a good surrogate marker for intra-abdominal fat, in all our patients.” And because the patients who received CT scans were also given a relatively new test called speckle tracking echocardiography, Muhlestein’s team was able to directly measure heart muscle function as well.

The study is only the latest to find that a person’s body shape, more so than their weight or BMI, can provide doctors with a clearer picture of their health. Other research has concluded that people with an apple-shaped body have a greater risk of disordered eating, fractures, and kidney disease when compared to those with similar BMI but a so-called pear-shaped body.

According to Muhlestein, while most obese people also tend to have higher than healthy levels of belly fat, our continuing reliance on BMI and weight alone may be leading doctors to miscategorize the cardiovascular health of many patients — not only those who are overweight, but also “skinny fat” people with a seemingly healthy BMI. “Based on my prior research and study of other trials, I estimate that more than 20 percent of patients might have a ‘reclassification’ of their cardiovascular risk if their waist circumference was measured along with their overall weight,” he said. The number of patients in the current study was too small, however, to determine if that could be the case here.

Regardless, if more research continues to affirm this connection, Muhlestein believes it may soon spark a change in how doctors determine disease risk. “If this trend holds, clinicians will need to begin measuring waist circumference on patients as an important vital sign,” he said.

Rather than simply supplanting BMI, though, the measure should be seen as an another instrument in the doctor’s toolkit. “The major way that I can see abdominal waist circumference being useful at present is that it can show which patients, among all overweight ones, are especially at risk and therefore should be especially vigilant,” he said. While all overweight people can benefit from lifestyle interventions like diet and exercise, he added, people with excess belly fat may need treatments that aggressively manage their blood pressure, cholesterol, and blood glucose levels to remain healthy.

Less certain for the time being is exactly why this sort of fat seems to be especially dangerous not only to our arteries but to the heart.

“We were actually somewhat surprised to see that heart muscle function was found to be related to waist circumference,” he said. “At present we don’t have any idea why intra-abdominal fat, more so than fat from anywhere else, can affect heart function in the absence of prior myocardial infarction.”

Muhlestein and his colleagues are now trying to devise studies that can definitively get to the root of that lingering question, and they plan to keep tabs on the study patients to see if their predictions hold true as well.

Source: Rosen B, Sharma R, Horton K, et al. Waist circumference is a strong predictor of regional left ventricular dysfunction in asymptomatic diabetic patients. The Factor-64 study. American College of Cardiology Annual Scientific Session. 2016.