How do we really measure our health?

Spring’s here – so how about doing a personal health ‘warrant of fitness’? But what do you check?

Weight is an obvious thing to keep track of, but it’s not necessarily the full picture. BMI – Body Mass Index – is another way. BMI is a measure of your fatness based on your weight divided by your height squared (BMI = kg/m2). But it’s often criticised for not taking into account fitness or body composition.

BMI is best used as a screening tool to identify whether or not a person might have a weight-related health issue. It’s also useful at a population level to measure overall levels of obesity. At that population level, as a nation, there’s no denying we are getting fatter.

But BMI is less reliable at an individual level. People often comment to that effect. “The BMI says I’m overweight, but that can’t be right!” is a common complaint. Another example used is of the All Blacks, some of whom would be technically obese based on their BMI alone.

However, the All Blacks are not typical of most people. While it is definitely possible to be overweight and still fit and healthy (and this is arguably better than being slim and unfit), I’d still suggest that of the people classified by the BMI as overweight or obese, few would fall into the ‘All Blacks’ category: highly athletic, lean individuals whose weight and height erroneously gives them an overweight BMI. Unless you are an elite athlete, the BMI is not a bad place to start.

That said, there are other ways to measure health which are potentially more useful. We’ve covered this in the November issue of Healthy Food Guide. One easy measure to take is waist circumference. It’s a simple DIY test: measure your waist halfway between the bottom of the ribs and the top of the hips (usually around the belly button). Again, there's individual variation, but the main point is that your health risk increases as your girth increases. For men, a waist circumference of 94cm or more is considered higher risk, with over 102cm considered substantial risk. For women, a waist over 80cm is an increased risk, and over 88cm is high risk.

Another measure is waist-to-height ratio. It's easy to remember the guideline: your waist circumference should not exceed half of your height. This applies to both men and women. So for example, if you are 170cm tall, your waist circumference should be no more than 85 cm.

Something else that’s worth measuring, although it’s a little more difficult, is body composition – in other words, how much fat and muscle you have. We all potentially lose muscle and gain fat as we get older, and this can be dangerous, whether or not we’re technically overweight. Even thin-looking people can have more body fat than is healthy. Having more fat, especially around the middle, is not great for men or women, as it increases our risk of diseases such as diabetes, heart disease and cancer. Losing muscle mass puts us at higher risk for osteoporosis, and also makes it easier to gain weight as we age – the more muscle we have, the more energy we burn, even when we’re not moving.

And of course there are the other things we can’t see, that are worth knowing. Your doctor can measure your blood pressure, blood cholesterol, triglycerides and blood sugar. Add in things like flexibility, resting heart rate, digestive function and sleep quality and you’ll be able to build a snapshot of your health. (Find out more in the November issue of Healthy Food Guide – do some of the tests and you might be surprised!) It’s important to remember that as with healthy eating, when it comes to how healthy our bodies are, we need to look at the big picture, not just the numbers on the scale.

First published: Nov 2014

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