Waist measurement is considered a better indicator of excess fat in adults than the Body Mass Index (mass in kg/height in m2). However, associated risk assessed on these measurements also needs to take onto account genotype. 8,12
Women of white European heritage with a waist circumference less than 80cm (about 31.5in) are considered at a lower risk of developing obesity-related health problems, while 80-88cm is considered higher risk, and more than 88cm is very high risk. 8,12 For women from African-Caribbean, South Asian and some other minority ethnic groups, a waist size of over 80cm (32in) is considered very high risk.13
For men (white European), a waist circumference less than 94cm (37in) is deemed low risk, 94-102cm is high, and more than 102cm is very high.8,12 For the non-white European ethnic groups, a male waist size of over 90cm (35.5in) is considered very high risk.13
The BMI can be used as a practical measure, but may not be as reliable, as very muscular people can have a high BMI without excess fat. As with waist measurement, the risk associated with BMI can also be influenced by ethnicity and age. Adults of Asian family origin generally have co-morbidity risk factors that are of concern at lower BMIs, while for older people these risks are associated with higher BMIs compared to the general population.8,12BMI bandings (for white European heritage people) with NICE and NHS Choices descriptors are:8,12

·      18.5-24.9 kg/m2 €“ healthy weight

·      25-29.9 kg/m2 €“ overweight

·      30-34.9 kg/m2 €“ obesity I or obese

·      35-39.9 kg/m2  €“ obesity II or obese

·      40 kg/m2or above €“ obesity III or severely obese

For South Asians, the BMI ranges are narrower, with a BMI of up to 23 kg/m2 being considered no higher risk, the range 23-27 kg/m2 being increased risk, and more than 27 kg/m2 being high risk.14
Combining waist and BMI measurements can therefore mean that people in the overweight BMI range but with low waist circumference are considered at no increased risk.12

Risk can be further considered with existing co-morbidities, which helps build the level of recommended intervention, with 1 being the lowest level of risk and 4 the highest level:12

Level of risk
Recommended level of intervention according to NICE CG189
1
General advice on healthy weight and lifestyle
2
Diet and physical activity
3
Diet and physical activity; consider drugs
4
Diet and physical activity; consider drugs; consider surgery
 

Note that NICE advises against using bio-impedance methods (measuring resistance to electrical conductivity through tissue) as a substitute for BMI as a measure of general adiposity.12