The body mass index (BMI) has been a steadfast measurement of health and wellness discussions for decades.
But new research says BMI may not mean as much as doctors once thought, at least when it comes to understanding cardiovascular risk in postmenopausal women.
A new study in the European Heart Journal reports that body shape, and specifically where fat deposits occur on the body, may be a better indicator of potential cardiovascular problems than BMI.
In this study, which was led by Qibin Qi, PhD, an associate professor at the Albert Einstein College of Medicine in New York, investigators looked at the body mass and fat distribution of more than 2,600 postmenopausal women.
Each participant was enrolled in the Women’s Health Initiative, a large-scale health study that recruited women between 1993 and 1998 and then followed them and their health until early 2017.
During that time, almost 300 women developed cardiovascular disease (CVD). The investigators found several unique factors about the women that could point to possible associations — and warnings — for other women.
First, participants with the highest percentage of fat around their middle and the lowest percentage of fat around their legs (the “apple” body shape) showed a threefold higher risk for cardiovascular disease than women with the lowest percentage of fat around their middle and the highest around their legs (the “pear” shape).
Second, women in the top quarter percentile of the most body fat around their middle had almost double the risk for cardiovascular health problems, like high blood pressure or stroke, compared to women in the top quarter percentile of the least body fat around their middle.
What’s more, women with the most fat around their legs had a 40 percent lower risk for cardiovascular disease compared to women with the least amount of fat around their legs.
Lastly, the investigators determined that overall body weight had little to do with eventual health risks. In these postmenopausal women, individuals with a normal weight could still have a high risk for CVD because of their body’s fat distribution around their middle.
In other words, weight didn’t appear to make any difference. It was the fat distribution — whether they were a “pear” or “apple” shape — that had the greatest impact on the study participants’ cardiovascular risks.
“Our findings suggest that postmenopausal women, despite having normal weight, could have varying risk of cardiovascular disease because of different fat distributions around either their middle or their legs,” Qi said in a statement.
“In addition to overall body weight control, people may also need to pay attention to their regional body fat, even those who have a healthy body weight and normal BMI,” he said.
So, should body shape replace BMI at the doctor?
BMI measurements are part of routine clinical care. Each time you come in for a checkup, a healthcare provider likely takes your height and weight and lets you know where you fall on the BMI chart.
It is, or at least has been, a reliable way to tell people if they were at an increased risk of health problems.
“BMI is a rough way to estimate the overall position of bodyweight health, but it does not take into account frame size,” said Thanu Jey, DC, chiropractor and clinical director of Yorkville Sports Medicine Clinic in Toronto.
Indeed, two people could have the same BMI but have vastly different body compositions.
One could be muscular; the other could have a large waist circumference from fat deposits. BMI would put them in the same spot, but their health is quite different. That’s where body shape may be important for analyzing health risks.
“BMI is good at finding a quick baseline and giving us an objective number to categorize. For the general population, BMI still serves to indicate increased health risks, but it’s important to know that there are exceptions,” Jey said.
“You can have a high BMI and still be healthy. The ‘apple shape’ gives us indirect information about a high waist circumference measure,” he said.
Can you change your fat distribution — and your risk?
According to the researchers, women who didn’t lose leg fat during the study but did reduce their proportion of belly fat cut their risk for cardiovascular disease.
The study found that this change alone could have prevented 6 out of 1,000 cases of CVD per year. That’s more than 100 cases over the course of the study.
This research from Qi and colleagues was the first to look at where fat is stored in the body and its association with cardiovascular risk in postmenopausal women. It’s unclear yet if these findings can be applied to any other populations.
“It is important to note that participants of our study were postmenopausal women who had relatively higher fat mass in both their trunk and leg regions,” Qi said. “Whether the pattern of the associations could be generalizable to younger women and to men who had relatively lower regional body fat remains unknown.”
But where your fat settles on your body is largely not up to you. Fat distribution is often the result of genetics and environmental factors, like diet and exercise.
You can try exercises that are targeted to reduce abdominal fat, but you’ll probably not be able to persuade your body to begin storing fat in your legs.
For now, BMI is going nowhere. But this study, along with others that call for a health-prediction scale with more nuance, may be chipping away at the stalwart index.
“Using BMI as an indicator for health ignores the simple fact that muscle weighs more than fat, and when you engage in strength training activity, your BMI is naturally higher,” said Rachel Fine, MS, RD, a registered dietitian, nutritionist, and founder of To The Pointe Nutrition.
Talk to your doctor about other measurements — like waist-to-hip ratio — that might be helpful in assessing your health.