How is obesity measured?

Measuring Obesity: An Overview

Obesity measurement is a crucial aspect of health assessment, especially in the United Kingdom, where obesity levels have been a growing concern. Accurately determining obesity helps in managing and treating this condition effectively. Several methods are used to measure obesity, each with its own advantages and limitations. This guide provides an overview of these methods to offer a clearer understanding of how obesity is assessed.

Body Mass Index (BMI)

Body Mass Index (BMI) is the most commonly used method for assessing obesity. It is a simple, cost-effective tool that calculates a person's weight in relation to their height. The formula involves dividing a person’s weight in kilograms by the square of their height in meters. In the UK, BMI is often used to categorise individuals into various weight statuses: underweight (BMI less than 18.5), healthy weight (BMI 18.5-24.9), overweight (BMI 25-29.9), and obese (BMI 30 or above). While BMI is widely used, it does not take into account muscle mass, bone density, or the distribution of fat, which can sometimes lead to misclassification.

Waist Circumference

Waist circumference is another method used to assess central obesity, which is an important risk factor for cardiovascular diseases. This method involves measuring the circumference around the smallest area of the waist, or if it is not visible, at the navel level. In the UK, a waist circumference of 94 cm or more in men and 80 cm or more in women is considered a risk factor. Unlike BMI, waist circumference provides insight into the level of visceral fat, which is more closely associated with health risks.

Waist-to-Hip Ratio (WHR)

The waist-to-hip ratio (WHR) measures the distribution of body fat by comparing the circumference of the waist to that of the hips. A higher WHR indicates a higher concentration of abdominal fat, which increases health risk. The World Health Organization considers a WHR above 0.90 in men and 0.85 in women to be indicative of a higher risk of obesity-related health issues. This method is significant as it considers where body fat is stored, which is an important determinant of health risks.

Body Fat Percentage

Body fat percentage provides a more direct assessment of an individual's fat content. Methods to calculate body fat percentage include skinfold measurements, bioelectrical impedance analysis, and dual-energy X-ray absorptiometry (DEXA). While these methods can provide a more comprehensive view of body composition, they are often more costly and require specialised equipment, making them less accessible for widespread public health assessments.