Better Than BMI

BMI is a very flawed system, and there are several more useful ways of measuring our bodies. Let’s take a look at them!

What’s wrong with BMI?

Oof, what isn’t wrong with BMI?

In short, it was developed as a demographic-based tool to specifically chart the weight-related health of working-age European white men a little under 200 years ago.

This means that if you are, perchance, not a working-age European white man in 1830 or so, then it’s not so useful. It’d be like first establishing height norms based on NBA basketball players, and then applying it to the general population, and thus coming to the conclusion that someone who is 6’2″ is very short.

In long, we did a deep-dive into it here, and in particular what things go dangerously wrong when it’s applied to women, non-white people, athletic people, pregnant people, people under 16 or over 65 and more:

When BMI Doesn’t Quite Measure Up

What we usually recommend instead

For heart disease risk and diabetes risk both, waist circumference is a much more universally reliable indicator. And since those two things tend to affect a lot of other health risks, it becomes an excellent starting point for being aware of many aspects of health.

Pregnancy will still throw off waist circumference a little (measure below the bump, not around it!), but it will nevertheless be more helpful than BMI even then, as it becomes necessary to just increase the numbers a little, according to gestational month and any confounding factors e.g. twins, triplets, etc. Ask your obstetrician about this, as it’s beyond the scope of our article today!

As to what’s considered a risk:

• Waist circumference of more than 35 inches for women
• Waist circumference of more than 40 inches for men

These numbers are considered applicable across demographics of age, ethnicity, and lifestyle.

Source: Waist circumference as a vital sign in clinical practice: a Consensus Statement from the IAS and ICCR Working Group on Visceral Obesity

Bonus extra measurement based on the above

Important also is waist to hip ratio.

How to calculate it:

1. measure your waist circumference
2. measure your hip circumference
3. divide the first measurement by the second one

Because it’s a ratio, it doesn’t matter what units you use (e.g. inches, cm, etc) so long as you use the same units for both measurements.

The World Health Organization offers the following chart:

Source: Waist Circumference and Waist-Hip Ratio: Report of a WHO Expert Consultation

This is especially relevant for cardiovascular disease risk:

Waist circumference and waist-to-hip ratio as predictors of cardiovascular events: meta-regression analysis of prospective studies

…and also holds true for all-cause mortality:

Waist-Hip-Ratio as a Predictor of All-Cause Mortality in High-Functioning Older Adults

An ancient contender that’s still more useful than BMI

Remember Archimedes? The (perhaps apocryphal) story of his “Eureka” moment in the bathtub when he realized that water displacement could be used to measure the volume of an irregular shape?

Just like Archimedes (who, the story goes, had been hired to determine the composition of a crown that might or might not have been pure gold), we can use this method to determine body composition, because we have references for how much a given volume of a given substance will weigh, so combing what we know about a body’s weight and volume will tell us about its composition in ways that neither metric could give us alone.

Indeed, it’s one of the commonly-mentioned flaws of BMI that muscle weighs more than fat, and Archimedes’ method not only avoids that problem, but also, actually turns that knowledge (muscle weighs more than fat) to our advantage.

It’s called “hydrostatic weighing” now:

Hydrostatic Weighing: Evaluation of body composition parameters using various diagnostic methods: A meta analysis study

You may be wondering: what about bones? Or internal organs?

The fact is that those are slightly confounding factors that do get in the way of a truly accurate analysis, but the variation in how much one person’s skeleton weighs vs another’s, or one person’s set of organs weigh than another’s, is too small to make an important difference to the health implications.

Lastly…

Hydrostatic weighing isn’t the only way to work out how much of our body is made of fat; if you have for example a smart scale at home (like this one) that tells you your body fat percentage, that is an estimate based on bioelectrical impedance analysis.

It’s less accurate than the hydrostatic method, but easier to do at home!

As to what percentages are “best”, healthy body fat percentages are (assuming normal hormones) generally considered to be in the range of 20–25% for women and 15–20% for men.

You can read more about this here:

Is A Visible Six-Pack Obtainable Regardless Of Genetic Predisposition?

Take care!