It’s widely recognised that body mass index (BMI) isn’t always the most accurate indicator of health, especially for individuals with athletic builds. However, despite its limitations, BMI has historically served as a useful initial assessment tool in clinical settings, especially when combined with other measurements.

But emerging evidence suggests that there may be an even more informative metric to consider instead of relying solely on BMI.

Leading medical experts have now warned that relying on BMI for diagnosing obesity is overly simplistic and can result in misclassification. A commission of over 50 international specialists highlighted that BMI often overestimates or underestimates obesity rates, failing to account for individual health factors. For instance, people with higher levels of muscle mass may be classified as having obesity despite having no signs of obesity-related illness, while others with excess body fat may go undetected.

In 2025, The Lancet commission called for a significant reform in how obesity is diagnosed, saying ‘BMI [is] useful but we need to go beyond BMI to determine excess body fat’. They also noted that it should be used only as a ‘surrogate measure of health risk’, concluding that obesity should be diagnosed using BMI only when supplemented by additional measurements, such as waist-to-hip ratio or waist-to-height ratio.

By incorporating markers like waist-to-hip ratio or waist-to-height ratio, healthcare professionals can efficiently assess their patients and gain a broader understanding of their health. In fact, a study published in Pediatric Research explored the potential superiority of waist-to-height ratio over BMI as a measure of health.

Now, new research adds further weight to the argument against relying on BMI alone. A study published in JAMA Network Open analysed data from 1,900 US adults aged 20 to 59 and found that a simple waist measurement could identify unhealthy levels of body fat that BMI alone may miss.

Researchers compared BMI and waist circumference with a more complex approach combining BMI, waist circumference, waist-to-height ratio and waist-to-hip ratio. While the more comprehensive method classified more people as having obesity, researchers found that waist circumference alone offered similar levels of accuracy. BMI alone, meanwhile, missed a substantial number of people who met the body-fat criteria for obesity.

‘Our findings show that you don’t necessarily need multiple complex measurements to identify obesity-related health risks,’ said lead author Aayush Visaria. ‘A waist measurement provides much of the information needed and is feasible for clinicians and patients alike.’

BMI (Body Mass Index) uses your height and weight to work out a measurement to gauge if your weight is healthy. The BMI calculation is:

Weight in kilograms divided by height in metres squared.

A BMI of 18.5 – 24.9 is deemed as healthy.

But individuals who are lean, possess greater muscle mass, and have a lower body fat percentage may exhibit a higher BMI compared to those with a higher body fat percentage and less muscle mass. This discrepancy arises because muscle is denser than fat per pound. While individuals with lower body fat percentages and higher muscle mass are generally considered healthier, BMI might not accurately reflect this distinction.

Although BMI isn’t universally suitable and doesn’t consider muscle mass, in a clinical setting, it serves as an easy and time-saving method for doctors to assess a patient’s health initially. Is it entirely ineffective? No. However, is it beneficial for everyone, particularly those with a higher muscle-to-fat ratio? Probably not, at least when considered in isolation.

BMI is frequently used in conjunction with waist-to-hip ratio for a more accurate measurement of health. The waist-to-hip ratio calculation is:

Circumference of the narrowest point of the waist in centimetres divided by the widest point of the hips in centimetres.

For men, a waist-to-hip ratio of less than one is deemed as healthy.

Waist-to-height ratio (WHtR), sometimes called waist-to-stature ratio (WSR), is also used as a marker of health. The WHtR calculation is:

Circumference of the narrowest point of the waist in centimetres divided by height in centimetres.

For men, a waist-to-height ratio below 0.5 or ‘waist less than half of height’ is deemed as healthy.

These aren’t the only studies that compares BMI and waist-to-height ratio. Another study, published by the Brazilian Archive of Digestive Surgery, found waist-to-height ratio to be superior to BMI in measuring cardiometabolic health.

NICE guidelines were reviewed in 2025, and the update encourages adults with a BMI below 35 kg/m² to measure their own waist-to-height ratio in conjunction with BMI. This could help indicate centrally stored adiposity (visceral fat around organs), which can be a helpful indicator of risk of illnesses.

If you suspect that your BMI results may be influenced by a higher degree of muscle mass, combining it with a waist measurement such as waist circumference or waist-to-height ratio may provide a more complete picture. For those with a higher body fat percentage, using these measurements alongside BMI may also help identify excess body fat that BMI alone could miss.

If you’d like to read more about the science cited in this article, here are the references:

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Kate is a fitness writer for Men’s Health UK where she contributes regular workouts, training tips and nutrition guides. She has a post graduate diploma in Sports Performance Nutrition and before joining Men’s Health she was a nutritionist, fitness writer and personal trainer with over 5k hours coaching on the gym floor. Kate has a keen interest in volunteering for animal shelters and when she isn’t lifting weights in her garden, she can be found walking her rescue dog.