According to Waist Circumference

Although waist circumference and BMI are interrelated, waist circumference provides an independent prediction of risk over and above that of BMI. Waist circumference measurement is particularly useful in patients who are categorized as normal or overweight on the BMI scale. At BMIs 35, waist circumference has little added predictive power of disease risk beyond that of BMI. It is therefore not necessary to measure waist circumference in individuals with BMIs 35.

The waist circumference at which there is an increased relative risk is defined as follows. Waist circumference cutpoints lose their incremental predictive power in patients with a BMI 35 kg/m² because these patients will exceed the cutpoints noted below.

Rationale: A high waist circumference is associated with an increased risk for type 2 diabetes, dyslipidemia, hypertension, and CVD in patients with a BMI in a range between 25 and 34.9 kg/m² (82). Monitoring changes in waist circumference over time may be helpful, in addition to measuring BMI, since it can provide an estimate of increased abdominal fat even in the absence of a change in BMI. Furthermore, in obese patients with metabolic complications, changes in waist circumference are useful predictors of changes in CVD risk factors (537).

There are ethnic and age-related differences in body fat distribution that modify the predictive validity of waist circumference as a surrogate for abdominal fat (526). These variations may partly explain differences between ethnic or age groups in the power of waist circumference or waist-to-hip (WHR) ratio to predict disease risks (429, 543). 

In some populations, waist circumference is a better indicator of relative disease risk than is BMI: examples include Asian Americans or persons of Asian descent living elsewhere (51, 273, 544). Waist circumference also assumes greater value for estimating risk for obesity-related disease at older ages. The table below incorporates both BMI and waist circumference in the classification of overweight and obesity, and provides an indication of disease risk.

Disease Risk* Relative to Normal Weight and Waist Circumference   BMI (kg/m2) Obesity Class Men 102 cm ( 40 in.) Women 88 cm ( 35 in.) Men >102 cm ( >40 in.) Women >88 cm ( >35 in.) Underweight 18.5   ----- ----- Normal+ 18.5 - 24.9   ----- ----- Overweight 25.0 - 29.9   Increased High Obesity 30.0 - 34.9 I High Very High   35.0 - 39.9 II Very High Very High Extreme Obesity 40 III Extremely High Extremely High

* Disease risk for type 2 diabetes, hypertension, and CVD.
+Increased waist circumference can also be a marker for increased risk even in persons of normal weight.