New Definition of Obesity Valuable for Risk Stratification

In January 2025, an international consensus guideline published in The Lancet Diabetes & Endocrinology proposed a new definition of obesity that incorporates anthropometrics and/or direct measures of body fat to better differentiate adipose tissue excess. The guideline also emphasizes combining measurement of excess adiposity with diagnosis of adiposity-related illness, introducing two new concepts:

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• Clinical obesity—Obesity with obesity-related organ dysfunction (hypertension, hyperlipidemia, diabetes, and obstructive sleep apnea are some of the many examples) and/or substantial, age-adjusted limitations of daily activities
• Preclinical obesity—Obesity with substantially preserved organ function and mild or no physical impairment related to obesity

Lindsay T. Fourman, MD, associate director of the Lipid and Metabolism Associates in the Endocrinology Division at Massachusetts General Hospital, Steven K. Grinspoon, MD, chief of the Metabolism Unit, and colleagues, recently completed the first study to comprehensively examine the clinical implications of the new obesity guideline.

In JAMA Network Open, they conclude that the new definitions of obesity and clinical obesity effectively stratify individuals at high risk of organ dysfunction and long-term complications.

Methods

The research group applied the new obesity definition to 301,026 participants in the All of Us research program, an effort of the National Institutes of Health to collect health data on at least one million people who reflect the diversity of the United States. All U.S. adults are eligible if they can provide consent.

This analysis included 301,026 individuals ages 18 to 80 (median age 54), 61% female and 39% male. 53.2% identified as white, 19.7% as Black or African American, 3.0% as Asian, 1.5% as American Indian or Alaska Native, 0.6% as Middle Eastern or North African, and 22.0% as another race. 18% identified as Hispanic/Latine.

When defining obesity according to the traditional definition based on body mass index (BMI), the researchers applied the World Health Organization’s race-specific BMI thresholds. When using the new definition, they applied the sex- and race-specific thresholds for anthropometric measurements given in the new guideline. They subclassified individuals into two mutually exclusive phenotypes:

• BMI-plus-anthropometric obesity—Body mass index (BMI) ≥30 kg/m2 plus at least one elevated anthropometric measure (waist circumference, waist-to-hip ratio, and/or waist-to-height ratio), or BMI >40 kg/m2
• Anthropometric-only obesity—At least two elevated anthropometric measures despite BMI below the traditional obesity threshold

Prevalence of Obesity

Application of the new definition led to substantial change in the prevalence of obesity:

• Had obesity by the traditional BMI-based criterion—43%
• Had obesity by the new definition—69%
• Had obesity by the traditional definition but not the new one—0.2%
• Did not have obesity by the traditional definition but were newly classified as having anthropometric-only obesity—26%

By the new definition, obesity was substantially more prevalent in older adults than young adults, affecting 78% of individuals age 70 or older compared with 44% of those ages 18 to 29.

Prevalence of Clinical Obesity

A diagnosis of clinical obesity was warranted for:

• 36% of all individuals
• 54% of individuals age 70 or older
• 53% of individuals with obesity
• 48% of individuals with anthropometric-only obesity 
• 56% of individuals with BMI-plus-anthropometric obesity (P<0.001 vs. anthropometric-only obesity)

Cross-Sectional Study of Health Conditions

Compared to individuals without obesity, individuals with BMI-plus-anthropometric obesity had 3.3 times higher odds of organ dysfunction and/or physical limitation, and individuals with anthropometric-only obesity had 76% higher odds, after adjustment for age, sex, and race.

Longitudinal Study of Health Outcomes

The median follow-up for this analysis was 4 years. Compared with the traditional definition, the new definition of obesity was associated with greater risk of certain adverse health outcomes:

• New-onset diabetes—adjusted HR, 2.60 by the traditional definition vs. 3.21 by the new definition
• Cardiovascular events (myocardial infarction, stroke, or acute heart failure)—aHR, 1.39 vs. 1.70
• All-cause mortality—aHR, 1.10 vs. 1.21

Among individuals with clinical obesity, compared to those without obesity or organ dysfunction:

• New-onset diabetes—aHR, 6.11
• Cardiovascular events—aHR, 5.88
• All-cause mortality—aHR, 2.71

Among individuals with preclinical obesity, compared to those without obesity or organ dysfunction:

• New-onset diabetes—aHR, 3.32
• Cardiovascular events—aHR, 1.40
• All-cause mortality—aHR, 1.09 (not a statistically significant difference)

These associations were consistent across age groups.

A Paradigm Shift

More than 75 professional organizations worldwide have already endorsed the new obesity guideline, marking a significant shift in how obesity will be conceptualized and classified. This study suggests the new definition of clinical obesity is important for identifying individuals with obesity who are at the highest long-term risk of diabetes, cardiovascular events, and mortality.

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