On January 14, 2025, The Lancet Diabetes & Endocrinology published its updated vision on the definition and diagnostic criteria for obesity.

By providing a new definition and diagnostic framework, the Commission, which was tasked with reviewing the definition criteria for obesity, proposes identifying when obesity is a risk factor (preclinical obesity) and when it represents a stand‑alone illness (clinical obesity).

The Commission, led by Professor Francesco Rubino of King's College London (United Kingdom), acknowledged that, even though obesity affects almost an eighth of the world’s population in varying degrees and forms, a global consensus has not been reached on its classification and definition.

The Commission was created in 2022 to evaluate new criteria for how doctors can address obesity and help patients.

People living with obesity have different profiles and health needs, but they are usually thought of as a monolith, defined only by body mass index—or, in millions of cases, not helped at all.

The new, evidence‑based definition distinguishes between two types of obesity:

Experts analyzed these concepts and reached a consensus on the limitations of body mass index (BMI). For this reason, the Commission used other measurements of body size, such as waist circumference, waist‑to‑hip ratio, and waist‑to‑height ratio, in addition to BMI to define obesity status.

Equal access to health care remains an important global problem. From the start, it was vital for the group of experts that the changes proposed by the Commission could be used and applied in diverse settings and locations.

Historically, BMI has been used because it is a simple, no‑cost way of measuring obesity. New measurements of body size should be equally affordable and easy to carry out.

In analyzing the cost‑benefit, the experts acknowledged that these new measurements would increase the workload and potentially the costs, but continuing with the current inaccurate diagnostic framework would also lead to higher medium‑ and long‑term costs for both the health system and patients.

Implementation of this new diagnostic framework should enable more affordable and effective treatment of obesity.

For people living with preclinical obesity, mitigating the risk will be a key priority, says the Commission. People with lower risk could be treated primarily through lifestyle changes; however, the experts said that more research is needed to identify those at increased risk who might require medical intervention.

How does this reframing of obesity change what we know about the epidemiology of the disease? To start, says the article:

The current epidemiological data on obesity prevalence, which are based on BMI alone, should be updated to reflect obesity as a spectrum of different medical presentations.

Databases should also include a more complete vision of the individual’s health status.

Additionally, there is ample opportunity for stratifying clinical obesity into different subtypes, possibly according to clinical presentation or pathophysiology, which should enable better management and understanding.

Adopting a new, more accurate approach for identifying obesity and changing social perceptions will require time and effort, but the key objective of these recommendations is to improve the lives of people living with obesity, says the international team.

One in eight people in the world has obesity. Obesity has become a global public health crisis, doubling in adults and quadrupling in adolescents since 1990.

In 2022:

This has dramatically increased the rate of preexisting conditions in that population, who usually develop them much later in life.

The Commission, created in 2022, has been a collaborative effort of 56 experts led by Rubino. At the time of publication, it had been endorsed by more than 75 international medical associations focusing on obesity care.

This story was produced using content from original studies or reports, as well as other medical research and health and public health sources cited in links throughout the article.