The Big BMI Debate

Emma Brown - Nutritionist | 04 May, 2014

Body Mass Index (BMI) has hit the headlines again this week, so I thought I'd have a quick look at the hype and the facts behind the news.

What is BMI?

BMI is a concept first developed over 150 years ago as a gauge to see how 'at risk' an individual was of premature illness or death. It's use expanded into healthcare, and BMI has been widely used as an international standard for obesity measurement since the 1980s.

Body proportion is measured as weight (in kg) over height (in m2) – so basically are you the right weight for your height. Seems simple right? Well maybe not because what it doesn't do is take into account other reasons for being disproportionately heavy for your height e.g. muscly athletes, rugby players and the suchlike, and some say it's out of date and not fit for purpose.

What's missing from BMI?

Science has moved on since BMI was developed, and we now know that it's not just body weight that is a risk factor when it comes to longevity. How weight is carried and in what tissues are also important factors – and one that BMI is unable to identify. This has got people thinking about whether BMI is actually worth the paper it's written on, and whether we should move away from it altogether to include more accurate measures of disease risk such as body fat percentage, or waist circumference.

There is no doubt that we get a better indication of someone's risk of diseases when we have more information about what's going on inside the body. Waist circumference, for example, helps doctors to see whether visceral fat (fat around the tummy) is an issue. Too much visceral fat has been linked to a higher risk of conditions such as heart disease.

Likewise, we now know that fat around the organs – particularly the liver and pancreas – is linked to a higher risk of Type 2 Diabetes. Again something that we can't measure by BMI.

So should we ignore BMI?

The simple answer is no – BMI remains a very useful tool to judge whether an individual MAY be overweight, and whether this MAY have an impact on their health. It's cheap and easy to use, and doesn't require lengthy and expensive tests. It gives an easy to understand 'answer' that tells us whether we need to delve further into a person's health and possibly take action.

Coupled with other more invasive diagnostic tests PLUS sensible advice on weight loss from a qualified healthcare professional, BMI is still one of a series of measures that helps us to identify people who needs to lose weight.

Nutritionist Emma Brown (ANutr), MSc Human Nutrition is passionate about how food science applies to the human body, and how the nutrients in what we eat affect us and ultimately have an impact on our health.