Obesity is graded according to BMI as:
- Healthy weight 18.5-24.9
- Overweight 25-29.9
- Obesity I 30-34.9
- Obesity II 35-39.9
- Obesity III 40 or more
Measures of overweight, obesity and central adiposity in adults
- use BMI as a practical measure of overweight and obesity. Interpret it with caution because it is not a direct measure of central adiposity
- in adults with BMI below 35 kg/m2, measure and use their waist-to-height ratio, as well as their BMI, as a practical estimate of central adiposity and use these measurements to help to assess and predict health risks (for example, type 2 diabetes, hypertension or cardiovascular disease)
People with a South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background are prone to central adiposity and their cardiometabolic risk occurs at lower BMI, so use lower BMI thresholds as a practical measure of overweight and obesity:
- overweight: BMI 23 kg/m2 to 27.4 kg/m2
- obesity: BMI 27.5 kg/m2 or above.
For people in these groups, obesity classes 2 and 3 are usually identified by reducing the thresholds highlighted by 2.5 kg/m2
Interpret BMI with caution in adults with high muscle mass because it may be a less accurate measure of central adiposity in this group.
Interpret BMI with caution in people aged 65 and over, taking into account comorbidities, conditions that may affect functional capacity and the possible protective effect of having a slightly higher BMI when older.
Waist to height ratio in adults:
Define the degree of central adiposity based on waist-to-height ratio as follows:
- healthy central adiposity: waist-to-height ratio 0.4 to 0.49, indicating no increased health risks
- increased central adiposity: waist-to-height ratio 0.5 to 0.59, indicating increased health risks
- high central adiposity: waist-to-height ratio 0.6 or more, indicating further increased health risks.
These classifications can be used for people with a BMI under 35 kg/m2 of both sexes and all ethnicities, including adults with high muscle mass.
The health risks associated with higher levels of central adiposity include type 2 diabetes, hypertension and cardiovascular disease
When talking to a person about their waist-to-height ratio, explain that they should try and keep their waist to half their height (so a waist-to-height ratio of under 0.5)
Define the degree of overweight or obesity in children and young people using the following classifications:
- overweight: BMI 91st centile + 1.34 standard deviations (SDs)
- clinical obesity: BMI 98th centile + 2.05 SDs
- severe obesity: BMI 99.6th centile + 2.68 SDs.
Use clinical judgement when interpreting BMI below the 91st centile, especially the healthy weight category in BMI charts because a child or young person in this category may nevertheless have central adiposity
Waist to height ratio in children
Define the degree of central adiposity based on waist-to-height ratio in children and young people as follows:
- healthy central adiposity: waist-to-height ratio 0.4 to 0.49, indicating no increased health risk
- increased central adiposity: waist-to-height ratio 0.5 to 0.59, indicating increased health risk
- high central adiposity: waist-to-height ratio 0.6 or more, indicating further increased health risk.
These classifications can be used for children and young people of both sexes and all ethnicities.
The health risks associated with higher central adiposity levels include type 2 diabetes, hypertension and cardiovascular disease
When talking to a child, young person, and their families and carers, explain that they should try and keep their waist to half their height (so a waist-to-height-ratio of under 0.5).
Reference:
- NICE (December 2006). Obesity guidance
- NICE (September 2022). Obesity: identification, assessment and management