For years, doctors, healthcare practitioners, and researchers have used the Body Mass Index (BMI), which is a ratio based on one’s weight and height, to determine whether one is overweight and to look at health outcomes. However, a new study has now found that a waist circumference to height ratio is a better measurement for the diagnosis of health outcomes, particularly liver disease.  

“Recent clinical consensus statements have emphasised a shift from diagnosing obesity with body mass index (BMI) requiring confirmation with surrogate markers such as waist circumference-to-height ratio (WHtR),” it says. 

They claim that this ratio of waist to height is a better “public health practice for obesity screening, diagnosis, and management.” 

“In a large multiracial US population with diverse age groups, the newly developed waist-to-height ratio cut points predicted the risk of liver steatosis and fibrosis in a dose-response manner,” it said.  

What is obesity and how is it measured?

Obesity, a chronic metabolic disease, is commonly diagnosed using BMI, a calculation based on weight and height. This BMI is commonly used to predict health outcomes. For instance, the US Center for Disease Control says that “BMI is a valuable population health measure used worldwide.” 

According to the WHO, “in 2021, higher-than-optimal BMI caused an estimated 3.7 million deaths from noncommunicable diseases (NCDs) such as cardiovascular diseases, diabetes, cancers, neurological disorders, chronic respiratory diseases, and digestive disorders.” 

Nevertheless, BMI has well-known drawbacks, including its inability to differentiate between muscle and fat mass, its failure to take into consideration the distribution of fat, and its accuracy varying with age, sex, and ethnicity. These flaws make it difficult to accurately predict associated health risks like liver disease and can result in both an overdiagnosis and an underdiagnosis of obesity. 

In fact, many experts have called out BMI as being an outdated measure and technique.

Dr. Anshita Aggarwal, assistant professor of endocrinology at Ram Manohar Lal Hospital and Medical College, New Delhi, had earlier pointed out that BMI does not offer a more holistic view of one’s health.  

“It looks at how much you weigh relative to your height, but not every 5-foot person with the same weight is obese versus healthy. BMI fails to distinguish between muscle and fat, does not account for fat distribution, and ignores critical factors like metabolic health,” she had said. 

Dr Anjana Bhan, an endocrinologist with over 30 years of experience at Max Healthcare, New Delhi, had said that these concerns were particularly pronounced in India and among South Asians worldwide. 

“South Asians are prone to what we call ‘lean fat’ — they may have a normal BMI but carry excess visceral fat, particularly around the abdomen, which increases their risk for diabetes and heart disease,” she had said, while adding that this was very common among Indians.  

What does the new study show?

The new study appears to echo these concerns and claims that “the simple and universally accessible WHtR (waist circumference to height ratio) cut points may be useful in clinical and public health practice for obesity screening, diagnosis, and management.” 

The study published in the Journal of the Endocrine Society says that waist-to-height ratio (WHtR) measurement is a more effective tool than the often used body mass index (BMI) for predicting liver steatosis and fibrosis in children and adults. The research, led by Dr. Andrew O. Agbaje, examined information from over 6,400 respondents to the 2021–2023 National Health and Nutrition Examination Survey (NHANES) in the United States. 

The participants were divided into three groups by the researchers based on their waist circumference to height ratio: excess fat mass (≥0.53), high fat mass (0.5 to <0.53), and normal fat mass (0.40 to <0.50). Transient elastography, a non-invasive imaging method that gauges liver stiffness (fibrosis) and fat accumulation (steatosis), was then used to evaluate liver health. 

They found that participants who fell in the category with the highest waist circumference to height ratio, or the excess fat mass category, “had nearly 3-fold higher odds of liver steatosis compared to those in high fat mass waist-to-height ratio categories.” 

“The findings were consistent across the races and age groups studied, suggesting that waist-to-height ratio cut points can be useful clinically and for public health screening, prevention, diagnosis, and management of obesity and its sequelae,” it said.  

In fact, they found that it was a better predictor than BMI for health outcomes. “The positive associations of BMI obesity categories with liver steatosis and fibrosis were significantly diminished or completely reversed when waist-to-height ratio was controlled for,” it said.  

“The odds of waist-to-height ratio excess fat in predicting liver steatosis are 6-fold higher than BMI-obesity,” it found.  

Based on a systematic review and meta-analysis of close to 30 studies, they concluded that this waist-to-height ratio had an “82% predictive accuracy” when it came to detecting Metabolically Associated Steatotic liver disease (MASLD), which was earlier known as the non-alcoholic fatty liver disease (NAFLD).   

“A recent study among 4444 participants diagnosed with MASLD from the NHANES third cycle survey conducted from 1988 to 1994 reported that waist-to-height ratio as a continuous variable was a stronger predictor of mortality than BMI,” it added.  

While the study is groundbreaking in its own right, it also highlights that further study may be needed on Asian populations to ascertain the cut-offs for people of this ethnicity. “A recent adult study suggests that Asians may have different waist-to-height ratio cutoffs, compared to Whites,” it says.  

It also said that future studies would also be needed to “validate the new waist-to-height ratio cut points against the risk of cardiovascular and all-cause mortality since these variables were not available in the current analysis.” 

Also read: Experts warn BMI no longer a reliable health indicator, urge better metrics