Body Mass Index Alone Is Unable to Predict Mortality Rate

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Body Mass Index (BMI) was developed as a metric to understand the body weight of individuals, but extensive amounts of evidence are indicating that this may not be the gold standard that it was once believed to be. BMI is a mathematical formula used to determine which category best fit an individual’s size based upon their weight and height. By dividing their weight in kilograms by the square of their height in meters, physicians could determine the fatness of an individual. This formula was then used to determine the group that the patient’s body type falls in, ranging from underweight to obese. BMI has long been used by practitioners in medical settings and clinical researchers to determine if the body weight and size of their patient is considered to be healthy, but this metric does not account for the full insight into extenuating factors that may potentially play a role in body shape. Multiple studies have shown that an optimal body weight is associated with health and longevity. However, understanding an individual’s body weight requires a more in-depth evaluation than what BMI alone can tell us. When researchers began examining the relationship between BMI and mortality risk, they found that this commonly used metric is not a useful stand alone measure in predicting the risk of death in patients.

“BMI has long been used by practitioners in medical settings to determine if the body weight and size of their patient is considered to be healthy, but this metric does not account for the full insight into extenuating factors that may potentially play a role in body shape.”

As of June 2023, physicians have been urged by the American Medical Association to discontinue using BMI as a single assessment to measure the overall health of their patients. Research is now finding that there are more efficient and accurate methods for assessing a patient’s overall health and predicting their longevity. One such method is using the patient’s waist to hip ratio. Metrics such as waist to hip ratio have proven to help account for extenuating factors that may affect the health of a patient. Waist to hip ratio can indicate excessive accumulation of fat around the midsection which has been linked to higher all-cause mortality. This increase of fat in the midsection can directly result in hypertension, cardiovascular disease, and diabetes, which are all the leading causes of premature death in the United States. Moreover, BMI fails to account for racial and genetic differences, which can be exceptionally limiting in medical settings, especially in a racially diverse country like the United States. For example, Hispanics have an increased likelihood to gain more weight centrally in their midsection. Due to the elevated risk of central obesity, Hispanics have their predicted risk of death starting at a lower BMI measurement than what is seen in other racial groups. BMI does have the ability to provide some level of insight into the patient’s health at a more general level but waist to hip ratio measurements provide additional information related to race, age, adiposity, and central obesity.

“Research is now finding that there are more efficient and accurate methods for assessing a patient’s overall health and predicting their longevity.”

Research conducted by Aayush Visaria, MD, MPH and Soto Setoguchi, MD, DrPH from the Rutgers University Institute for Health analyzed recent health survey data collected from 1999 to 2019 to develop a better understanding of the correlation of BMI with mortality risk. The investigators found that if an individual was overweight or had a healthy weight, their weight had almost no effect on their mortality risk. In their analysis, the risk of death increased significantly for adults with a BMI of 30 or higher (obese) while such an increase was not seen in adults who had a BMI between 22.5 (healthy weight) and 29.9 (overweight). Surprisingly, in the age group of 65 years or older, the risk of death was virtually the same for individuals with a normal weight, overweight, or obese (with a BMI up to 34.9). Based on these findings, they concluded that measures of adiposity other than BMI are necessary to better estimate the predicted risk of mortality in relation to body weight. Individuals who had a BMI of 18.5 or under (underweight) also had an increased risk of mortality. While BMI can be used as a helpful tool to gather a general idea of weight and body shape, these results suggest that it should not be used as a freestanding measurement to determine health and longevity.

“He states that other measures of adiposity are necessary to better understand the predicted risk of mortality in relation to the weight of an individual because BMI fails to show the whole story of their health.”

The intended goal of BMI is to provide an indication of fatness, but it fails to account for other key components of health such as cardiovascular health, body fat percentage, muscle strength, waist to hip ratio, etc. By focusing on metrics that evaluate these extenuating factors, physicians can better predict the patient’s mortality risk by gaining deeper insight as to how the body weight of their patient is affecting their health. While it is well recognized that elevated BMI may contribute to conditions that pose an all-cause mortality risk (such as hypertension, cardiovascular disease, and diabetes), BMI is an unreliable indicator of mortality risk on its own. Practical recommendations from these findings is to interpret BMI conjointly with other metrics, as it does not provide sufficient insight into the overall health of patients.

Amanda Johnson Amanda is a recent graduate from the University of Southern California where she received her degree in Psychology. In addition to her university studies, she earned her Integrative Nutrition Health Coach certification from the Institute of Integrative Nutrition (IIN).

This article was reviewed and approved by Emeran Mayer, MD