Bodyweight or BMI – which is the best metric for fitness? Neither!

I recounted in an earlier post my experience of weight loss that was hardly apparent to people around me. Many years before that attempt at weight loss, however, I was, in fact, squarely in the middle of the range for ‘ideal bodyweight’. Or so said the Body Mass Index (BMI) chart that adorned the dull walls of my GP’s clinic. As a young girl just barely out of her teenage, however, I was still disappointed by the number on the scale – I had enough ‘issues’, one might say, regarding my body image. If I had known then that, in relation to my height, my weight was very reasonable, as per BMI norms, I might have had more body confidence. But then, again, I would have been chasing the wrong ideal.

Is BMI a better indicator of health and fitness?

We now know that the absolute number on a weighing scale does not mean much by itself. Is BMI a better indicator of health and fitness? It is more complex than the bodyweight metric, but it is definitely inadequate on many counts, and possibly no better. Bodyweight is a critical factor in BMI calculation. As we know, bodyweight is comprised of lean body mass and body fat. However, BMI calculation does not discern between these components. And that is how the cookie crumbles.

Two men with the same age, height and weight, and resultantly the same BMI, should, in theory, have the same level of fitness and/ or degree of risk of lifestyle disease. But what if one of them has a body fat percentage of 10% while the other has 30%? The former has far greater lean mass, and likely more muscle, than the latter, meaning greater strength and no/ low obesity, indicating a lower risk of lifestyle disease. One look at the BMI numbers for some celebrities is enough to realise how meaningless the index really is when comparing one individual with another.

If one has to throw out bodyweight as well as BMI, then what is one left with to gauge health and fitness levels? The singular metric that indicates if you are in a healthy range or not, is your body fat percentage. The proportion of fat in the body indicates how close you are to the ideal body composition for fitness. Among men, the ideal range for body fat percentage is 4% (elite athletes) to 15%, and among women, 8% (elite athletes) to 20%.

Admittedly, it is a little more complex to gauge body fat percentage than getting on a weighing scale or plugging in height and weight measurements into a formula. Skin fold measurements using calipers, bioelectric impedance analysis (BIA), dual energy X-ray absorptiometry (DEXA scanning), air displacement plethysmography, and hydrostatic weighing are the most well known methods, in increasing order of accuracy, complexity, accessibility and cost.

The singular metric that indicates if you are in a healthy range or not, is your body fat percentage.

Along with cardio-respiratory endurance, muscular endurance, musculoskeletal strength and flexibility, ideal body composition rounds out the five components of fitness.

There, you now know what you have to shoot for! If there are lingering doubts, feel free to ping me in the Comments section.

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