Understanding the New Obesity Definition: Implications and Insights

Introduction to the Evolving Definition of Obesity

In recent years, the definition of obesity has undergone significant reexamination, leading to a broader understanding of this complex health issue. Previously, obesity was primarily defined by a body mass index (BMI) of 30 or higher. However, a new definition reflects advancements in medical understanding, thus increasing the number of individuals classified as obese. This change is a crucial development, necessitating a deeper exploration of its implications for health policy and education.

The Impact of a Broader Definition

The revised definition of obesity expands the criteria used to assess an individual's body weight in relation to their height, reflecting a more comprehensive approach to health. This shift acknowledges that health outcomes are not solely determined by numerical values but also by genetic, metabolic, and lifestyle factors. As a result, more individuals may be diagnosed with obesity, emphasizing the need for meaningful interventions and support systems.

Raising Awareness and Understanding

With the increase in the number of individuals defined as obese, it becomes imperative for society to foster awareness and understanding of this condition. Public health campaigns must adapt to educate about the newly defined parameters. Emphasizing the multifactorial nature of obesity can encourage empathy and reduce stigmatization, fostering a more inclusive dialogue about health and wellness.

Additionally, healthcare professionals must stay informed about the implications of the new obesity classification. This knowledge will enable them to provide appropriate care tailored to the needs of a larger patient population. By recognizing that obesity may involve various health determinants, practitioners can offer holistic treatment plans that address physical, emotional, and psychological well-being.

To effectively combat obesity, it is essential to consider preventive measures that extend beyond individual behavioral changes. Community programs that promote healthy eating, active living, and mental wellness will play a pivotal role in addressing this public health challenge. Such initiatives should be designed so that they accommodate the newly recognized population of individuals affected by obesity, promoting a healthier lifestyle for all.

In conclusion, the new obesity definition expands the number of individuals classified as having this condition, necessitating a shift in how society and healthcare systems approach obesity. By fostering awareness and understanding of the complexities surrounding obesity, we can better support those affected and work towards solutions that promote overall health and well-being for everyone.

About 1 in 5 people considered overweight based on BMI alone would be classified as having obesity based on the European Association for the Study of Obesity’s (EASO’s) new framework aimed at defining obesity beyond BMI.

The EASO framework defines obesity as a BMI ≥ 30 or BMI ≥ 25 and waist-to-height ratio ≥ 0.5, plus any obesity-related medical, functional, or psychological complications. It was published in July 2024 in Nature Medicine.

The new study, published on July 7, 2025, in Annals of Internal Medicine (AIM) using 1999-2018 data from the US National Health and Nutrition Survey (NHANES), suggests that people previously considered overweight by BMI between 25 and < 30 who are now considered to have obesity based on the EASO framework appear to be at an increased risk for mortality compared with people with normal weight with no comorbidities. However, they are not at an increased risk compared with adults with normal weight who do have comorbidities.

The finding that 1 in 5 would be reclassified was unexpected, lead author Dror Dicker, MD, head of Department of Internal Medicine and Obesity Clinic at the Hasharon Hospital-Rabin Medical Centre of Tel Aviv University, Tel Aviv, Israel, told Medscape Medical News.

“It’s a high number…What clinicians should take from this is that even people who are so-called living with overweight can be defined as living with obesity, meaning they have a higher risk for mortality, and by definition, more complications…These patients in the past were transparent,” Dicker said.

The aim of the EASO definition, he said, is “We want to treat obesity very early, very effectively to prevent deterioration. To do so, we have to find those patients who really have the disease.”

Several Recent Obesity Definitions Go Beyond BMI

The EASO framework is just one of several recent attempts to develop a new definition for obesity that accounts for central adiposity and comorbidities as well as BMI. An analysis of another one, BMI — Specific Waist Circumference Thresholds proposed by the International Atherosclerosis Society (IAS) and the International Chair on Cardiometabolic Risk (ICCR) Working Group, was published in the same issue of AIM. And in January 2025, The Lancet Commission proposed a new classification as either a disease “clinical obesity” or a risk factor “preclinical obesity.”

In an editorial accompanying the two new papers, AIM Senior Deputy Editor Christina C. Wee, MD, along with two other AIM editors, wrote “Before we can build consensus on the best universal approach to define and risk stratify obesity, we need more head-to-head comparisons of the performance of these different tools in diverse populations.”

Wee and colleagues added, “Ultimately, for these more nuanced frameworks to be useful, they need to be tested in therapeutic trials to see whether they identify patients most likely to benefit from intervention. With the expansion of effective obesity treatment options, it’s time we match our advances in therapeutics with improvements in diagnosis and risk assessment.”

The new EASO and the IAS-ICCR framework studies, Wee and Colleagues said, “offer new insights but also highlight the challenges of this task.”

1 in 5 Would Be Re-Classified

Of the 44030 adults in NHANES who met eligibility criteria, 31.3% were considered to have normal weight based on the World Health Organization definition (BMI < 25), 33.3% had overweight (25 to < 30), and 35.4% had obesity (≥ 30). Based on the EASO definition, 18.8% of the “overweight” group is now classified as having obesity.

Those newly classified as having obesity had more comorbidities, with 57.5% having at least one and 42.5% having more than one, compared with just 34.3% and 38.7%, respectively, of those with obesity based on BMI alone. The most common comorbidities were hypertension (79.9%), arthritis (33.2%), diabetes (15.6%), and cardiovascular disease (10.5%), all of those proportions higher than those with BMI-defined obesity except diabetes, 60.3%, 28.2%, 19.0%, and 8.6%, respectively.

After adjustments, compared to those with normal weight and without comorbidities, those with EASO-defined overweight were not at an increased risk for mortality during follow-up (hazard ratio [HR], 0.80; P = .107), but those with EASO’s new definition of obesity (HR, 1.50; P < .001) were. However, those with normal weight and comorbidities (HR, 1.74; P < .001) and BMI-based obesity were at even greater risk (HR, 1.82; P < .001).

“If you compare the overweight cohort to those with normal weight and no comorbidity or complication, then there is a higher risk for mortality. This is the real comparison…Take the overweight cohort and then separate those who are healthy and those who are not healthy. Then you will find the high risk,” Dicker said.

But, asked to comment, The Lancet Commission author Geltrude Mingrone, MD, PhD, professor of internal medicine, Catholic University, Rome, Italy, and professor of diabetes and nutrition, King’s College London, London, England, pointed out that the EASO-defined obesity through a risk-based framework, while The Lancet Commission proposed a clinical disease model.

“The findings highlight a significant limitation. Although the EASO criteria reclassified about 1 in 5 US adults as having obesity, this reclassification did not correlate with a substantially higher risk of death when controlling for other variables.”

The new study results, she said, “suggest that comorbidities themselves, not necessarily the EASO-defined obesity, may be driving the increased risk. The findings imply that the EASO definition, while potentially useful for identifying morbidity risk and guiding clinical care, does not significantly enhance mortality prediction beyond traditional BMI thresholds. This raises concerns about the clinical and public health relevance of redefining obesity in terms that do not align with clear prognostic differences.”

Redefining obesity has also proved challenging in the US, Obesity Expert Donna H. Ryan, MD, professor emerita at Pennington Biomedical Research Center, Baton Rouge, Louisiana, told Medscape Medical News. “There is a huge discussion in the obesity community about how to better identify who needs to be treated for obesity. Unfortunately, the primary care community is not there yet. They don’t regularly code for obesity…even though the BMI is a core measure reported in the electronic record at every visit. Most of the effort is to shift to a measure of central fat measurement, but most offices don’t even have a tape measure and if they do, they don’t measure regularly or correctly.”

Better methods are needed, Ryan said. “We need to get out of the dark ages with the tape measure…Good alternatives are DEXA and digital anthropometry. These can both give measures of central adiposity and total body fat. The time has come to use some 21st century tools…I hate to say it, but these efforts at a better diagnosis of obesity seem to be focused on excluding people from treatment, not on identifying who really needs treatment.”