BMI and the concept of obesity
Firstly, the term obese is most commonly used in conjunction with Body Mass Index (BMI). The BMI measure is a very simple calculation: your total weight in kilograms, divided by the square of your height in meters. But what is weight here? On this scale, the weight of our muscles, our blood, our organs, and indeed our bones are all lumped together with the weight of our fat, and assessed together to give us an assessment of our health. But anyone who has trained with weights, or has physical work, anyone who is naturally broad across the shoulders, many non-white ethnic groups, or indeed anyone who is shorter than average will have a BMI which doesn’t really reflect their true state of health.
Further, BMI can grossly misjudge someone as healthy, who may have lower than average muscle mass or someone who, through lifestyle factors we will get into later, has what little fat they have in the wrong place – i.e. around their organs. These factors may lead a doctor to send someone away thinking they have nothing to do to improve their health from a weight/composition point of view, but they would be very wrong.
These problems with BMI are well known. It is widely acknowledged that it is a terrible way to measure and talk about weight and composition. So why is it still used? Simply put, it is completely reproducible. Any doctor, without much equipment, can weigh someone, and measure their height. This means that they can reach a BMI figure in seconds that is indisputable.
So the first reason we never use the o-word is because it is most commonly used around BMI, and at My Vital Metrics, we will never talk about your BMI, except to deride its uselessness.