How we diagnose and define obesity is set to change

Obesity: A Complex Health Issue

Obesity is linked to many common diseases, such as type 2 diabetes, heart disease, fatty liver disease, and knee osteoarthritis.

Obesity is currently defined using a person’s body mass index, or BMI. This is calculated as weight (in kilograms) divided by the square of height (in metres). In people of European descent, the BMI for obesity is 30 kg/m² and over.

What’s Wrong with BMI?

The risk of ill health depends on the relative percentage of fat, bone, and muscle making up a person’s body weight, as well as where the fat is distributed.

Athletes with a relatively high muscle mass, for example, may have a higher BMI. Even when that athlete has a BMI over 30 kg/m², their higher weight is due to excess muscle rather than excess fatty tissue.

People who carry their excess fatty tissue around their waist are at greatest risk of the health problems associated with obesity.

New Definition of Obesity

The goal of the Lancet Diabetes & Endocrinology Commission on the Definition and Diagnosis of Clinical Obesity was to develop an approach to this definition and diagnosis. The commission, established in 2022 and led from King’s College London, has brought together 56 experts on aspects of obesity, including people with lived experience.

The commission’s definition and new diagnostic criteria shifts the focus from BMI alone. It incorporates other measurements, such as waist circumference, to confirm an excess or unhealthy distribution of body fat.

What Does This Mean for Obesity Treatment?

Clinical obesity is a disease requiring access to effective health care.

For those with clinical obesity, the focus of health care should be on improving the health problems caused by obesity. People should be offered evidence-based treatment options after discussion with their health-care practitioner.

Treatment will include management of obesity-associated complications and may include specific obesity treatment aiming at decreasing fat mass, such as:

• support for behaviour change around diet, physical activity, sleep, and screen use
• obesity-management medications to reduce appetite, lower weight, and improve health outcomes such as blood glucose (sugar) and blood pressure
• metabolic bariatric surgery to treat obesity or reduce weight-related health complications

Should Pre-Clinical Obesity Be Treated?

For those with pre-clinical obesity, health care should be about risk-reduction and prevention of health problems related to obesity.

This may require health counselling, including support for health behaviour change, and monitoring over time.

What Happens Next?

These new criteria for the diagnosis of clinical obesity will need to be adopted into national and international clinical practice guidelines and a range of obesity strategies.

Once adopted, training health professionals and health service managers, and educating the general public, will be vital.

Conclusion

Obesity is a complex health issue that requires a nuanced approach to diagnosis and treatment. By shifting the focus from BMI alone to a more comprehensive assessment of body fat and its distribution, we can better identify those at risk of health problems and provide more effective treatment options.

FAQs

Q: What is the new definition of obesity?

A: The new definition of obesity is based on a person’s body fat distribution and the presence of health problems associated with excess body fat.

Q: How is clinical obesity diagnosed?

A: Clinical obesity is diagnosed based on 18 diagnostic criteria, including signs and symptoms of ongoing organ dysfunction and/or difficulty with day-to-day activities of daily living.

Q: What is pre-clinical obesity?

A: Pre-clinical obesity is a condition characterized by high levels of body fat that are not causing any illness. People with pre-clinical obesity are at higher risk of developing diseases such as heart disease, some cancers, and type 2 diabetes.

Q: How is pre-clinical obesity treated?

A: Pre-clinical obesity is treated with health counselling, including support for health behaviour change, and monitoring over time. Depending on the person’s individual risk, they may opt for one of the obesity treatments mentioned above.