Is BMI outdated? UK study reveals waist-hip ratio as the key predictor of mortality

Body Mass Index (BMI), a standard measure of body fat based on weight and height, has long been used to assess health [1]. However, a UK study has proposed that waist-to-hip ratio may be a more reliable predictor of mortality than BMI.

BMI has been the go-to tool for evaluating whether a person’s weight falls within a healthy range. It’s a straightforward calculation: weight (in kilograms) divided by height (in meters squared).

Despite its widespread use, critics argue that it oversimplifies the complexity of human health [2, 3]. BMI doesn’t account for variations in body composition, such as muscle versus fat, and it doesn’t consider where fat is located in the body.

The study in question, conducted in the UK, involved over 42,000 participants and spanned two decades [4]. Its findings suggest that waist-to-hip ratio, a measure of fat distribution, could be a more accurate predictor of mortality than BMI.

The waist-to-hip ratio is calculated by dividing the waist and hip measurements. A higher ratio indicates more fat around the waist relative to the hips.

A growing body of research has linked excess abdominal fat, often reflected in a higher waist-to-hip ratio, to various health risks, including heart disease, diabetes and certain cancers [567].

The study found that individuals with a higher waist-to-hip ratio were more likely to die prematurely, regardless of their BMI. In other words, people with similar BMI values but different fat distributions could have various mortality risks.

One of the study’s key takeaways is that BMI may provide a partial picture of an individual’s health. It doesn’t distinguish between fat and muscle nor consider where fat is stored in the body.

For instance, two individuals with the same BMI could have vastly different visceral fat levels, which surrounds organs and poses a greater health risk.

These findings have led to a broader discussion about the limitations of BMI. Many experts acknowledge that while it’s a simple and convenient tool for assessing weight-related health risks on a population level, it may need to offer more precision for individual health assessments.

Critics argue that BMI can misclassify individuals as healthy when they have hidden health risks due to abdominal fat [8].

Conversely, it can label individuals with a healthy fat distribution as overweight or obese based solely on their weight and height.

This isn’t the first time alternative BMI measures have been proposed. Waist circumference, which directly assesses abdominal fat, has gained attention recently.

The waist-to-hip ratio is another such measure, focusing on fat distribution. These measurements offer more insights into the potential health risks associated with excess body fat [9].

In conclusion, the UK study highlights the potential limitations of BMI as a standalone health assessment tool.

While BMI remains useful for quickly evaluating weight-related health risks in populations, more is needed to provide a comprehensive view of an individual’s health.

Assessing factors like waist-to-hip ratio or waist circumference could offer a more nuanced understanding of health risks associated with body fat distribution.

Nonetheless, it’s important to remember that no single measurement can provide a complete picture of health and a holistic approach that considers multiple factors is often necessary for a thorough health assessment.

Learn more about this research in JAMA Network Open.


Photograph: microgen/Envato
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