Overweight BMI Doesn't Predict Mortality In Most People

A new study has found that BMI is not a reliable predictor of mortality for most people.

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Concerned about your BMI? You can take a sigh of relief. A new study finds that being overweight does not necessarily mean you have a higher risk of death. According to the new study, published in the journal PLOS One, body mass index (BMI) is not a reliable predictor of mortality for most people, including those who are classified as overweight.

Body mass index is a measurement of a person’s weight divided by the square of their height. It’s traditionally been used as a non-invasive, quick, and easy way to measure a person’s body fat percentage. But for years, experts have claimed that BMI is an inaccurate measurement because it does not consider bone density or muscle mass.

And now, a team of researchers from Rutgers University has published research that pokes even bigger holes at the use of BMI in clinical settings.

The research team reviewed data from 554,332 American adults, 50% of whom were women and 69% non-Hispanic white. Data points included height, weight, and age, as well as a number of socio-economic factors. Follow-ups were performed after an average of nine years but went as far out as 20 years. In that span, the team recorded 75,807 deaths and found that the risk of death was similar across many BMI points.

The research also found that there was no increased mortality risk in older adults — 65 or older — with BMIs ranging from 22.5 to 34.9. (A BMI of 25 to 29.9 is considered overweight, and a BMI over 30 is considered obese.) Similarly, younger adults with BMIs between 22.5 and 27.4 also had no increased mortality risk. But importantly, adults with BMIs over 30 did have an increased mortality risk — anywhere from 21% to 108%.

While overweight or obese BMIs can be a risk factor for disease, BMI alone is not a good indicator of mortality risk. “Our study highlights the increasing reservations of using BMI alone to drive clinical decisions. There is no clear increase in all-cause mortality across a range of traditionally normal and overweight BMI ranges; however, that is not to say that morbidity is similar across these BMI ranges. Future studies will need to assess incidence of cardio-metabolic morbidities,” wrote the research team.

The new study comes on the heels of a report from the American Medical Association (AMA) stating that BMI is not an adequate predictor of health. The AMA recognized the historical harm BMI has caused to women and minorities, noting that the data points used to categorize a person’s BMI as underweight, healthy, overweight, and obese were all calculated using white men. The calculation does not account for age, sex, race, or ethnicity. Despite these failings, physicians have consistently used the metric for decades to quantify a person’s overall health, and many continue to do so.

The AMA encourages doctors not to base health solely on BMI and called on insurance companies to stop using BMI as the “sole criterion to deny appropriate insurance reimbursement.”

There are numerous factors that go into determining your level of health and fitness. Activity levels, the sedentary nature of your work, diet, genetics, and ethnicity should all be considered. Studies have shown that small amounts of physical exertion, even a five-minute walk, can improve health outcomes, and workouts that include some strength training are better for your heart than cardio alone. Minor tweaks to your routine can mean significant returns when it comes to health, fitness, and longevity.

The big picture is that the number on a scale does not determine your overall health. Health is individual and varies across demographics and should not be represented by one number that was developed by doctors decades ago.