BMI alone doesn’t accurately predict life expectancy, new study finds

Does your body mass index, or BMI, predict your life expectancy? Although it has long been believed that being “overweight” on the BMI spectrum will negatively impact your health and your longevity, new research suggests this may not always be true.

Your BMI is determined by your height and weight. For many decades, the BMI was used as a gold standard to determine if a person was in a “normal” or “healthy” range of weight. But in recent years, many experts have been challenging the usefulness and accuracy of the BMI calculator.

And now a new study published in the journal PLOS One has provided more evidence of the unreliability of using BMI as a sole health indicator.

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The Results From the New Study

Rutgers University researchers analyzed the health data of 554,000 non-pregnant adult Americans, as collected by the National Health Interview Study from 1999-2018. They compared that data to the 2019 U.S. National Death Index to see if there was a correlation between a person’s BMI and life expectancy.

They discovered that healthy people — without any other serious health issues — could be considered “overweight” on the BMI scale and not have any increased risk of death. The findings “have consistently shown no significantly different mortality risk for overweight-range BMI,” the authors wrote.

“The real message of this study is that overweight as defined by BMI is a poor indicator of mortality risk, and that BMI in general is a poor indicator of health risk and should be supplemented with information such as waist circumference, other measures of adiposity (fat) and weight trajectory,” said study co-author Dr. Aayush Visaria to told CNN.

In analyzing death risk, they also found that when a person is over 65 years of age, their BMI did not have any demonstrable impact on their longevity if it was less than 26.5. The study also found that young people with a BMI higher than 27.5 did have a 20% increased risk of mortality, but BMI categorizes people as overweight at 25.

Waist Circumference Could Be A Better Measure

Naturally, more research needs to be done, and there are some limitations to the study. However, the researchers did find that waist circumference does seem to have a connection to a person’s death risk.

“People with elevated waist circumference had a higher risk of mortality compared to normal waist circumference within the same BMI groups,” Visaria told CNN. “In the overweight BMI range (25-29.9), the risk of mortality was 17-27% higher among people with elevated waist circumference compared to lower waist circumference.”

Waist circumference matters so much because so-called deep belly fat comes with serious potential health risks. Known as visceral adipose tissue (VAT), this kind of fat increases inflammation in the body, which can lead to insulin resistance and an increased likelihood of diseases like heart disease and colon cancer.

While “brown fat” is essential to help regulate body temperature and burn energy, visceral adipose tissue is “white fat.” While all bodies need fat, white fat can be dangerous in excessive amounts. Belly fat is almost always made up of “white fat,” which your body stores when you eat too many calories.

Previous research has shown that belly fat and death risk are closely associated. One 2020 study found that for every 10 centimeters of belly fat, a woman’s risk of death from any cause increases by 8%. For men, this risk of death increases by 12% per every 10 centimeters of belly fat.

In 2021, the American Heart Association highlighted the importance of your waist circumference, saying that this number might matter just as much as the number on the scale.

“Studies that have examined the relationship between abdominal fat and cardiovascular outcomes confirm that visceral fat is a clear health hazard,” National Institute of Health’s Dr. Tiffany Powell-Wiley said to CNN.

How to Reduce Your Waist Circumference

You can gain health benefits from aerobic exercise that helps to reduce your waist circumference, even if the number on the scale doesn’t change.

“Reaching a target of 150 minutes a week of physical activity, particularly aerobic physical activity, may be enough to help reduce abdominal fat,” said Powell-Wiley. “This decrease in abdominal fat without weight loss may be related to increasing fat-free mass (or muscle mass) with aerobic exercise.”

In other words, instead of focusing on shedding pounds and lowering your BMI, focus on moving your body and getting your heart pumping. Even if you don’t see the results on the scale right away, you are likely having a positive impact on your health and life expectancy.