Forget BMI: Simple waist test reveals real obesity risk as you age, study finds

As the UK population continues to age, obesity and obesity-related diseases are placing an increasing burden on the NHS. Researchers say adopting more accurate screening tools—such as waist-to-height ratio—could help identify older adults at risk earlier and enable timely preventive care.

Waist-to-height ratio (WHtR) provides a better reflection of visceral fat, which is stored around the abdomen and has a greater impact on internal organs. This type of fat is more strongly linked to conditions such as heart disease, stroke and dementia, making WHtR a more meaningful measure of health risk than BMI alone.

The study, conducted by researchers from the Universities of Sheffield and Nottingham, analysed obesity trends in England between 2005 and 2021 using data from the Health Survey for England. The team compared BMI—the most commonly used measure of obesity—with waist-based indicators, including waist-to-height ratio.

Co-authors Dr Laura Gray from the University of Sheffield and Dr Magdalena Opazo-Breton from the University of Nottingham examined whether rising obesity trends were primarily driven by ageing, environmental factors, or generational differences.

Dr Laura Gray, from the University of Sheffield’s School of Medicine and Population Health, said:

“BMI is a well-known and widely used measure, but it can be misleading—particularly for older adults and those with lower muscle mass—into thinking they are not at risk of obesity.

“Waist-to-height ratio is easier to understand and remember than complex BMI categories, including for children. People can easily check their own risk using a measuring tape. If your waist is less than half your height, that’s a good indicator you’re at a healthy weight.”

She added:

“Our findings show that increases in obesity are largely driven by environmental changes over time, not just individual behaviours. This highlights the need for broader, systemic action from policymakers, particularly around the food environment.

“The likelihood of obesity also increases with age, meaning an ageing population could further raise prevalence. If we under-diagnose obesity in older adults by relying solely on BMI, we risk missing large numbers of people who could benefit from healthcare interventions.”

The researchers found that waist-to-height ratio provides a clearer and more consistent indicator of health risk as people age. Unlike BMI—which tends to rise in middle age and decline later in life due to muscle loss—waist-to-height ratio continues to increase steadily, better mirroring the growing risk of obesity-related diseases in older adults.

The findings also challenge the widespread belief that carrying extra weight in later life may be protective, instead underscoring the importance of maintaining a healthy waist size throughout ageing.

The study adds further support to guidance from the National Institute for Health and Care Excellence (NICE), which recommends using waist-to-height ratio alongside BMI.

The researchers reinforce a simple public health message: “Keep your waist circumference less than half your height.”