Could the Body Roundness Index Replace BMI?

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When my oldest son was in high school, we got a Wii Fit. The first time he played it, he was putting his stats into the game—height, weight, age, sex—and his little Mii guy went from the average size to a larger one. My son threw the remote, said “This is stupid,” and never played it. 

Body mass index (BMI), a calculation of height-to-weight ratio, has been used for many years by researchers and the medical community to determine one’s health status and risk. But it’s flawed—big time. For example, athletes with greater muscle mass, like my son, will naturally weigh more. So according to the BMI charts, he was “obese” for his height. But the reality was that his body fat percentage was low and his lean tissue—including muscle and bones—was high, providing a healthy body composition.

BMI also cannot determine where body fat is distributed. We know that visceral or belly fat, the fat that lies deeper in the abdomen and surrounds vital organs, can put people at higher risk for disease and death when there’s too much of it (some of it is necessary to help cushion the organs). But two people with the same BMI may have dramatically different builds. One may carry more fat in their lower body—hips, legs and butt—while the other carries more fat in their middle. So they weigh the same and are the same height, but because they carry fat in different places, the one with more visceral fat could be at higher risk for chronic inflammation, heart disease, diabetes and cancer. 

Thankfully, researchers have caught on, and there is now a newer, hopefully more accurate, way to determine health risk—the Body Roundness Index (BRI). It’s calculated using an equation incorporating height, weight and waist circumference. And a newly released study published in JAMA Network Open on June 5, 2024, highlights the use of BRI in determining the risk of dying prematurely from anything, referred to as all-cause mortality. Let’s see what it shows.

How Was This Study Conducted and What Did It Show?

Researchers used data from the National Health and Nutrition Examination Survey from 1999 to 2018. NHANES is a series of surveys done to monitor the public health of the U.S. population and is conducted every two years. Surveys are done via in-home interviews and mobile examination centers. 

A total of 32,995 adults, half male and half female, with an average age of 47 at the beginning of the study period, were used for this study. There was a racial and ethnic mix that included Mexican American, non-Hispanic Black, non-Hispanic White and other races and ethnicities—American Indian, Alaska Native, Native Hawaiian, Pacific Islander and non-Hispanic Asian. 

Since researchers were looking at death rates during the study period up to December 31, 2019, mortality data was obtained through the Centers for Disease Control and Prevention’s website and linked to the NHANES database. 

Covariates—variables that may or may not affect or skew results—included age, sex, race and ethnicity, education level, poverty income ratio, smoking status, drinking (alcohol) status, family history of heart disease and family history of diabetes. Covariates also allow researchers to see if there are trends within any of the variables—like if age or education level affects risk for disease or death.

Several statistical analyses were run on the data, before and after adjusting for the covariates. 

Because BRI is so new, categories and ranges—like, low, normal and high BRI—have not yet been established. Because of this, researchers needed to create their own categories. At the study’s halfway point, researchers noticed a U-shaped association between BRI and deaths. From this, they formed various categories called quintiles with Q1 being the lowest BRI and Q5 the highest. Q3 was assigned as the reference group. 

What they found was very interesting. Because it’s been shown in previous studies that higher amounts of visceral (belly) fat place people at higher risk of chronic disease and death, it might not be surprising that these researchers found that people who fell into Q5—which suggests a high level of visceral fat—were 50% more likely to die from any cause compared to the reference group (Q3). 

But what might be unexpected is the finding that people who fell into Q1—suggesting very low visceral fat—were 25% more likely to die from any cause compared with adults in Q3. This was especially true in individuals aged 65 and older. 

What gives?

Researchers explain that very low BRI has been linked to poor nutritional status, fatigue, reduced activity tolerance and muscle atrophy. In other words, people with very low BRI tend to be malnourished and lose a lot of muscle. This results in fatigue and not being able to be physically active.

Digging further into the results, those in Q5 tended to die more often from cardiovascular and metabolic disorders—like heart disease and diabetes—and cancer. This was true even in those who had a “normal” weight—because you can fall into a “normal” or “healthy” BMI or weight category and still carry a higher proportion of fat in your middle. 

How Does This Apply to Real Life?

While body shape and placement of fat deposits on your body are largely determined by genetics and stage of life—menopause tends to shift fat storage to the middle in women—there are things you can do to help keep visceral fat in a healthy range.

For example, there is evidence that a diet high in fruits, vegetables, lean protein, healthy fats and fiber—basically a Mediterranean diet eating pattern—combined with physical activity, is a great combo to help combat visceral fat. 

Lack of sleep and chronically high stress levels also encourage belly fat accumulation. When stress is chronic, the stress hormone cortisol is constantly buzzing around in your body. Cortisol does several things, including encouraging fat storage in, you guessed it, the abdomen. 

As far as physical activity goes, a combination of aerobic exercise and strength training goes a long way toward keeping visceral fat in a healthy range. It’s important to note that spot training—like doing planks and abdominal crunches—will strengthen the core muscles but does not reduce fat in that area. 

Interestingly, a 2023 study in JMIR Public Health and Surveillance suggests that even “weekend warriors”—people who get most of their physical activity in over the weekend—showed reduced levels of belly fat similar to those who were more consistently active. This suggests that all activity counts, so if you’re not currently engaging in physical activity, just start moving more and go up from there.

The Bottom Line

This 20-year study followed 32,995 American adults and found that those with very low and high amounts of belly fat had 25% and 50% higher rates of premature death, respectively. Following a healthy eating pattern like Mediterranean diet, engaging in regular physical activity, getting enough quality sleep and reducing your stress levels all play a role in reducing visceral fat around your abdomen. 

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