Study finds waist-to-height ratio better predicts obesity risk with age

As muscle mass declines and abdominal fat rises with age, BMI can be misleading. A new study finds waist-to-height ratio better reflects real obesity risk in older adults

A large-scale study suggests that the waist-to-height ratio (WHtR) may be a more accurate way to identify obesity-related health risks in older adults than the widely used body mass index (BMI). Researchers say BMI can underestimate risk as people age, potentially leaving many older adults unaware of their true metabolic and cardiovascular vulnerability.

 

What the study found

 

The findings come from a study titled “Long-term trends in central obesity in England: an age-period-cohort approach”, published in the International Journal of Obesity. Conducted by researchers from the University of Sheffield and the University of Nottingham, the analysis examined data from over 120,000 people aged 11 to 89 years using the Health Survey for England between 2005 and 2021.

 

 

The researchers compared several obesity measures, including BMI, waist circumference, waist-to-hip ratio and waist-to-height ratio. They found that while BMI tends to rise in midlife and then decline in older age, measures of central obesity, especially waist-to-height ratio continue to increase steadily with age, better reflecting real-world health risks.

 

Why BMI may fall short in older adults

 

BMI calculates obesity based on weight and height but does not distinguish between muscle and fat. As people age, muscle mass naturally declines while fat, particularly around the abdomen, often increases. This can result in an older person having a normal BMI despite carrying excess abdominal fat linked to diabetes, heart disease and metabolic disorders.

 

“BMI is a really well-known and well understood measure. However, it could be misleading people, particularly older people and those with less muscle mass, into thinking they are not at risk of obesity," said co-author Dr Laura Gray, University of Sheffield's School of Medicine and Population Health.

 

The study showed that BMI followed an inverted U-shaped pattern, peaking in middle age and falling after around 65. In contrast, waist-to-height ratio rose consistently into later life, aligning more closely with the known rise in obesity-related illnesses among older adults.  "Visceral fat isn't just stored energy. It is metabolically active tissue that drives inflammation, disrupts insulin signalling, and accelerates the path toward Type 2 diabetes and cardiovascular disease. This is why we see so many people develop diabetes at BMIs that would be considered normal," explained Dr Gagandeep Singh, Founder of Redial Clinic, New Delhi and specialist in Metabolic Medicine and Diabetes Reversal.

 

What makes waist-to-height ratio different

 

Waist-to-height ratio focuses on central fat distribution, which is considered more harmful than fat stored elsewhere in the body. It is calculated by dividing waist circumference by height.

 

Key advantages highlighted by the researchers include:

 

• It captures harmful abdominal fat more accurately
• It reflects obesity risk across the life course, including older age
• It uses a single cut-off for adults, children and older people, making it easier to interpret

 

A simple rule of thumb

 

Public health experts often describe WHtR with a simple message - 'Keep your waist to less than half your height.'

 

“Waist-to-height ratio is also a lot easier for people to understand and remember than more complex BMI categories, particularly in children. People can easily check their own risk with a measuring tape. If your waist is less than half your height, that’s a good indicator you’re at a healthy weight,” shared Dr Gray.

 

According to the study, a waist-to-height ratio above 0.6 signals a high risk of obesity-related complications, regardless of age or sex.  "The simple rule of keeping your waist below half your height gives patients an actionable, measurable target they can track at home without any equipment beyond a measuring tape. It shifts the conversation from chasing a number on the scale to addressing what actually predicts metabolic risk," added Dr Singh.

 

Why this matters for public health

 

The researchers warn that relying on BMI alone could mean missing obesity-related risks in ageing populations, especially as the UK population continues to get older. Their findings support wider use of waist-based measurements in both clinical settings and community health screening.

 

“If we under-diagnose obesity in older adults because we're relying solely on BMI,  then this could mean we fail to identify large proportions of people who are at high risk and can benefit from healthcare interventions,” notes Dr Gray.  "This finding is especially critical for Indians. The Indian phenotype is often characterised as 'thin outside, fat inside'—individuals who appear lean but carry dangerous amounts of visceral fat around their organs. BMI routinely misses these patients, giving them false reassurance while they silently progress toward insulin resistance and metabolic disease. Waist-to-height ratio captures this hidden risk far more effectively," said Dr Singh. 

   

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This report is for informational purposes only and is not a substitute for professional medical advice.