obesity (grading of)

Last edited 09/2022 and last reviewed 07/2023

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 (2)

• 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.

BMI in children (2):

• 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

Reference:

1. NICE (December 2006). Obesity guidance
2. NICE (September 2022). Obesity: identification, assessment and management