Measuring obesity
When you consider the serious hazards associated with overweight and obesity (high blood pressure, stroke, heart disease and several common cancers), the public health implications of having such an overweight population come into sharper focus. However, it’s now becoming increasingly clear that not all people who are overweight or obese have the same health risk profile. The explanation for this may lie in the way that these people are classified in terms of their bodyweight, and indeed, this was highlighted in a presentation at the Nutrition Society’s Annual Summer Meeting at DIT a couple of weeks ago.
The figures quoted for the Irish population above have been derived using a measurement called BMI or “body mass index”, which in simple terms indicates the person’s weight for height. It’s calculated by squaring the person’s height in metres and dividing their weight in kilograms by this figure (i.e. weight (kg)/ (height (m)). Unfortunately, BMI gives no indication as to that individual’s body composition. So there’s an assumption being made that the person’s increased bodyweight is attributable to an excess of body fat; an assumption which may or may not be true. To give an example, some athletes (especially those involved in power disciplines like rugby, sprinting, weight-lifting and boxing) are heavy for their weight. In these cases, however, their increased weight for height which sees them classified into the “overweight” or “obese” BMI categories is attributable to muscle, a situation which actually reduces their risk of the serious disorders highlighted above.
