The BMI is one of the oldest and most pervasive measures of a healthy weight. Devised by a Belgian statistician back in the 1830s , it’s one of the methods the NHS uses to determine who qualifies for gastric band surgery , the guideline used by GPs to determine weight-related risk factors and a number which many are expected to agonise over – despite their seemingly svelte appearance. Yet it seems nary a month passes without headlines appearing, challenging the BMI’s validity – so why is it still so commonplace?
The Limited Value of the BMI
The BMI is based on a very simple calculation: your weight divided by your height squared. The obvious problem this sum throws up is that it doesn’t address body composition. As our understanding of fat and the role it plays in human health has advanced, we’ve learned to distinguish, not only between “good” and “bad” fat, but between the threat posed by fat accumulations in different areas . It turns out that body composition is far more important than overall weight – you can have a perfectly normal BMI, and still have high levels of visceral fat (internal abdominal fat which is stored near the organs and is widely believed to be the most dangerous type of fat) .
This is important because visceral fat increases your risk of all kinds of health problems: cancer, stroke, heart disease, diabetes and arthritis, to name but a few . It increases insulin resistance, as well as interfering with your body’s hormones , making it a lot more important to address than unsightly, but relatively harmless, subcutaneous fat (fat stored under the skin, that you can pinch ).
With our relationship to our fat so much more complicated than previously believed, it stands to reason that such a simple calculation couldn’t hope to reveal our body’s inner secrets. Or could it?
Alternatives to the BMI
Actually, the BMI’s more reliable replacement could involve an even simpler calculation than that of the BMI itself. The waist-to-hip ratio and the waist-to-height ratio are both gaining repute amongst the scientific community as the most accurate indicators of future fat-related health problems. Both are designed to measure the level of abdominal fat a person is carrying, in an attempt to estimate visceral fat levels – although it’s important to be aware that fat stored around the middle may be subcutaneous as well as visceral . Nevertheless, a protruding belly and a large waist are a reliable indicator of dangerous visceral fat levels.
The Hips Don’t Lie…
Both methods are incredibly simple to work out – to calculate your waist-to-hip ratio, simply stand up straight, relax your stomach (no cheating!) and use a tape measure to check the circumference of the spot where your ribs meet your hips, about an inch above your belly button. Then measure around the widest parts of your hips (the thickest part of your buttocks), and divide your waist measurement by your hip measurement. A healthy ratio is 0.9 or less in men, and 0.85 in women.
The HTW ratio is a demonstrable improvement on the BMI , but it’s still been subject to some criticism – namely, that as an individual loses weight they’re likely to lose it from both the hips and the waist, resulting in an unaltered ratio. This isn’t always the case – being a natural “apple” shape (someone who tends to store fat around their middle) is one of the risk-factors for fat-associated diseases – but the waist-to-height ratio circumvents this potential flaw entirely, and is even easier to work out.
Similar to the HTW ratio, all you need to do is measure your waist and your height – if your waist measurement is less than half your height, you are in the clear. In fact, you don’t even need a tape measure for this one – just get a piece of string (or even dental floss, at a pinch) and cut it to the length of your body, halve it and check whether it will go around your waist. A recent study from Leeds Beckett University found this was more accurate than either the BMI or the HTW method .
It’s the Measure, of All Things
Ultimately, the scientific community’s reservations about the BMI have been documented for years now – but its widespread use continues regardless. Even some GPs aren’t fully clued up on the latest research into body fat calculations, so if your doctor is telling you your BMI indicates you need to lose weight but you live an active lifestyle and eat well, don’t panic. Measuring your waist using one of the above methods is a far more reliable method of determining your risk level and it’s easy to do at home – so step off the scales and measure your way to a healthier future.
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