Obesity is defined as an excess of body fat. Different methods can be used to determine the degree of adiposity, with body mass index (BMI) being a commonly used indirect method. BMI is defined as weight in kilograms divided by the square of height, in metres. According to the WHO BMI classifications, obesity is defined as BMI ≥30 kg/m², while overweight is defined as 25 ≤ BMI < 30 kg/m².
Diet Quality: An Evidence Based Approach, Volume 2 p. 3-27