It would be fantastic if there was a single number out there which you could use to say “I am n healthy”, knowing that you could improve n and directly improve your health.
One attempt at that is the body mass index (BMI) that doctors use to state generally that someone is overweight or underweight. However, the BMI values can be wildly inaccurate depending on your body type – whether you are male or female, European or Asian, active or sedentary.
BMI calculates purely on the weight and height of the person. This gets you a figure that is a good start. For example, my height is 168cm, and my weight this morning was 73.7kg. That gives me a BMI of 26.1 which is classed as “overweight”.
But what does “overweight” mean? When something is “over” or “under”, that means there is an ideal number that should be looked for. When someone says that “your BMI indicates you are overweight”, what they mean is that “an average person with your height and weight has a higher mortality than an average person with your height and a lower weight”.
Of course, no-one actually is average. I have short legs, for example. If they were 4cm longer(172cm) and I had the same weight (73.7kg), I would have a lower BMI (24.9) and no longer be considered overweight.
Some people are sedentary and have fat around the torso, while some people may work out a lot. If my weight was due to extra muscle instead of extra fat, would I still be overweight? Having less fat on the body means that I would be less likely to develop diabetes or heart diseases, so that means that even though the BMI suggests that an athletic 73.7kg 168cm man is overweight, he would actually be more healthy than a sedentary man who weighed 66kg and was considered “normal” weight.
Because the BMI was supposed to be based on the fat content of the body, it makes sense that a more accurate measure of that fat content would take these differing physiologies into account.
The Surface-Based Body Shape Index (SBSI) is a calculation which provides a more accurate index of fat content. It was published in 2015, based on data from 11,808 healthy adults, and provides a much more accurate prediction of health than the BMI does.
To measure the SBSI, you need to measure your height, weight, vertical torso circumference and waist circumference. The first two are used in BMI calculations as well, but the later two give a more discriminate calculation, for example in the case of people with shorter legs *ahem* (affecting the vertical torso circumference), or who are athletic instead of sedentary (affecting the waist circumference).
After calculating the index (here’s an online calculator), you will have a number. That number is the SBSI.
According to table S1 in the research paper, healthy people have an SBSI of .105 (female) or .108 (male).
That number is a general indicator of health. A definite number to be aimed for, rather than a range of weights that might be right or not.
Mine at the moment is .113, so I need to work on getting that down to .108.
My goal at the moment is to work on getting my weight down to 66kg anyway, even though there is no definite reason for that, but while working towards that, I will also be working on reducing my waist circumference to 84cm.
Just a thought, but I wonder if it’s possible to come up with a formula, using the data from that report, that instead of just giving a general fat content index, can accurate predict the percentage chance of death within the next 5 years? Hmm…