Nearly 70% of Americans may be obese under new norms, study warns

Researchers warn that the findings reflect a growing global health crisis, as outdated BMI standards fail to capture hidden fat-linked risks contributing to chronic disease

Nearly 70 per cent of adults in the United States would now fall under the category of obesity if a new medical definition were applied, according to a major study published in JAMA Network Open.

 

The research highlights growing scientific consensus that Body Mass Index (BMI) alone is an incomplete indicator of health risk. Experts say the shift could reshape how obesity is diagnosed, treated, and covered by healthcare providers.

 

What the study found

 

Researchers analysed data from more than 301,000 adults aged between 18 and 80 across the US for the study titled 'Implications of a New Obesity Definition Among the All of Us Cohort'.

 

 

Using the traditional BMI threshold (BMI=30), around 43 per cent of participants were identified as obese.

However, applying the new hybrid definition, which incorporates body-fat distribution measures, obesity prevalence jumped to 68.6 per cent.

 

The rise was observed across all demographic groups:

• Men showed a greater relative increase at 32.5 per cent, than women at 21.7 per cent.
• Among racial and ethnic groups, Asian Americans saw the steepest jump, from roughly 27 per cent to over 51 per cent.
• In older adults aged 70 years and above, the figure reached 78 per cent.

“We already thought we had an obesity epidemic, but this is astounding. With potentially 70 percent of the adult population now considered to have excess fat, we need to better understand what treatment approaches to prioritise,” said Lindsay Fourman, lead author of the study, endocrinologist at Mass General. She is also an assistant professor at Harvard Medical School.

 

Going beyond BMI

 

The updated definition, proposed by the Lancet Diabetes & Endocrinology Commission in January this year, expands the way obesity is identified. This would encompass people either with a BMI greater than 40, or those with a high BMI and at least one raised figure for:

• Waist circumference
• Waist-to-hip ratio
• Waist-to-height ratio
• Direct fat measures

 

In addition, they said obesity should be split into two categories:

• Clinical obesity – where excess fat is already affecting organs or metabolism, with signs of illness
• Pre-clinical obesity - where excess fat is present but without visible dysfunction

 

Under the new framework, a person can fall into one of two new categories:

• BMI-plus-anthropometric obesity – high BMI plus at least one elevated waist or hip measure
• Anthropometric-only obesity – normal BMI but at least two or more elevated body-fat distribution measures.

 

Spotting hidden health risks

 

Traditional BMI fails to capture fat distribution, which plays a key role in metabolic and cardiovascular health. Central or abdominal fat, even at a lower overall weight, can increase risks of diabetes, heart disease, and organ stress.

 

“We have always recognized the limitations of BMI as a single marker for obesity because it doesn’t take into account body fat distribution,” said senior author Steven Grinspoon, Mass General and Harvard Medical School.

 

“Seeing an increased risk of cardiovascular disease and diabetes in this new group of people with obesity, who were not considered to have obesity before, brings up interesting questions about obesity medications and other therapeutics,” he adds.

 

The team noted that more research is essential to unravel what drives anthropometric-only obesity and to determine how best it can be managed or treated.

 

What it means for public health

If nearly 70 per cent of US adults qualify as obese, it signals that the true burden of obesity-related risk could be far greater than previously believed.

 

The shift could have major implications for:

• Clinical practice – encouraging doctors to assess waist and fat distribution, not just BMI.
• Public health policy – expanding eligibility for preventive programmes and treatments.
• Insurance and health systems – adjusting coverage criteria for obesity-related care.

 

What individuals can take away

 

BMI is only part of the story. Even if your BMI is in the normal range, high abdominal fat can raise health risks. Experts recommend:

• Tracking waist-to-height ratio as a simple at-home measure.
• Maintaining a balanced diet rich in fibre, fruits, and lean protein.
• Engaging in regular physical activity, particularly strength and cardio training.
• Getting periodic health screenings for blood sugar, cholesterol, and blood pressure.