Fit and fat: Is BMI the best way to tell if you're healthy?

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1. Labelled 'fat'

Around 60% of adults in the UK are overweight or obese, according to a 2013 study by the Institute for Health Metrics and Evaluation. They are labelled this way because of their body mass index, or BMI.

We’re used to the idea that being fat is harmful. But some people who have a high BMI are relatively safe when it comes to the risk from serious conditions such as diabetes or heart disease. Meanwhile, people with a supposedly ‘healthy’ BMI could still have a high risk of developing health problems.

Some argue that BMI, which dates back to the mid-19th Century, is no longer fit for purpose. Research suggests there may be other, more accurate measures of individual health.

2. Check your BMI

BMI chart

It’s easy to work out your BMI, which is calculated using your weight and height. Simply look at the chart above and find out how your BMI classifies you.

3. Not for everyone

BMI has become a popular way to quickly and cheaply gauge fatness – and therefore health. But it doesn’t always work well for everyone.

BMI doesn't distinguish between fat, muscle and bone. This means it doesn't necessarily tell us how much body fat we have.

People with a lot of muscle bulk can have a high BMI, even if their body fat is low. On the other hand, some older people who lose their muscle with age could see their BMI fall into the ‘healthy’ range, despite carrying too much fat.

BMI also doesn’t take into account where the body fat is. Research shows that people who carry a lot of fat around their waists are at higher risk of health problems than those with more fat around their thighs and buttocks.

So waist size may be a better way to monitor your health than BMI.

4. Measure your waist

Wrap a tape measure around your waist – defined as midway between the bottom of your ribs and the top of your hips. Does your waist size put you at risk?

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Women with a waist of 31.5” (80cm) or more may be at increased risk of heart disease, type 2 diabetes and stroke. The risk is much higher at 34” (88cm) or more.

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Men with a waist of 37” (94cm) or more may be at increased risk of heart disease, type 2 diabetes and stroke. The risk is much higher at 40” (102cm) or more.

5. The vital health check

While waist size may be a better indicator of health than BMI, it too still has its limitations.

It isn’t recommended for use in children, as it doesn’t take into account a person’s height. Waist size increases with age, and it can’t be used in pregnancy. It may also need to be adjusted for ethnicity. For example, East Asian and South Asian men may be more susceptible to diabetes than Caucasian men with the same waist size.

Beyond body shape and size, there is one test that has been shown to correlate extremely well with health.

This test, known as VO2max, measures the amount of oxygen your body uses while exercising as hard as you can. VO2max is a useful way of measuring aerobic fitness. And in studies, people with higher levels of aerobic fitness lived to an older age.

Regular aerobic exercise is the obvious way to get fitter. But whatever your BMI or waist size, you can still improve your general fitness levels by becoming more active in daily life – be that doing the gardening, cycling to work, or walking instead of driving. Any exercise that makes you slightly breathless helps to improve your aerobic fitness.