The body-mass index is a valuable measure of obesity and overweight. It is calculated from an individual’s weight and height. Measuring waist circumference helps in screening for potential health risks that are associated with overweight and obesity. The BMI for underweight individuals below 18.5, normal is 18.5-24.9, overweight is 2.5-29.9 and above 30.5 is regarded as obese. BMI is not only a good gauge of an individual’s risk for conditions such as type 2 diabetes, hypertension, and heart disease but is also an estimate for body fat. In adults, most of the adipose tissue is found around the waist and the hips. Waist size greater than 40 inches for men and 35 inches for women poses a high risk for health complications.
Validity and Reliability of BMI tool
The BMI using waist circumference is used to provide a rough estimate of an individual’s body fat. It correlates to some degree with more accurate measurements such as DEXA X-ray scans and bio-impedance scales. However, the BMI using the waist circumference tool can underestimate or overestimate fatness in certain people. The tool has its limitations as it does not directly measure an individual’s fat. Therefore, it is not the most valid or reliable tool for determining body fat levels.
Sensitivity, Reliability, and Prediction of Values
The BMI using waist circumference is a less sensitive tool for identifying cases with co-morbidities resulting from over-weight and obesity in short-stature subjects. The proficiency of BMI using waist circumference as a diagnostic tool is poor is short-stature subjects. This limitation cannot be solved by decreasing the BMI thresholds used to explain overweight and obesity. The tool is not the most reliable because it does not directly measure a person’s body fat levels. The predictive values in BMI show a strong correlation between obesity and BMI high scores. Thus the BMI is a good predictor of various abnormalities in a given population.
Lam, B. et al. (2015). Comparison of body mass index (BMI), body adiposity index (BAI), waist circumference (WC), waist-to-hip ratio (WHR) and waist-to-height ratio (WHtR) as predictors of cardiovascular disease risk factors in an adult population in Singapore. PLoS One, 10(4), e0122985.