“Overweight and obesity are terms used to define excess body weight in the form of fat causally linked to poor health and wellbeing. The National Association of Clinical Obesity Services (NACOS) recognises obesity with health impairment as a chronic disease.”

This is in line with the majority views of people with obesity and health care professionals, dictionary definitions of ‘disease’, as well as the positions of many other national and international organisations including the World Health Organization, World Obesity Federation, American Medical Association, Canadian Medical Association, Obesity Canada, Scottish Intercollegiate Guidelines Network, Israel Medical Association, Royal Australasian College of Physicians, and at a government level, Portugal and Italy.

Obesity is commonly classified using the body mass index (BMI), which is calculated by dividing weight in kilograms by height in metres squared (expressed in kg/m2 units). While a population specific BMI of 30 or more is used to define obesity, intensive medical therapy may be considered as an adjunct to lifestyle interventions for individuals with a BMI >27 and weight-related complications.

Bariatric surgery may be considered for individuals with a BMI ≥40 or BMI ≥35 with at least one weight-related comorbidity, which is typically used to define clinically severe obesity.