BMI is flawed as a way of assessing healthy weight. That’s the working assumption at the heart of a major new study of 100,000 Britons – a £43m imaging project being carried out by universities including Oxford, Edinburgh and Imperial College, as well as the Medical Research Council.
That assumption will surprise few in the fitness sector, which has long been aware of the limitations of BMI. As Tom Stillman, head of business development for Boditrax, summarises: “BMI has been enormously useful for population surveys, demonstrating the strong links between excess weight and chronic ill health, but it can be misleading on an individual basis. It doesn’t take into account variables such as age, race or natural changes in body composition over time. Neither does it reflect the fact that, if exercise is built into a weight loss programme, a greater proportion of body fat will be lost compared to weight loss through diet only.”
And so it was that, at a launch event for the new study, professor Paul Matthews of Imperial College London was able to present a slide that showed the scans of 60 people, all with a BMI of around 30. Among these allegedly unhealthy people were elite athletes as well as sedentary, genuinely overweight people; one of BMI’s many limitations is that it can’t differentiate between muscle, fat and bone, so even Olympic athletes can be classified as obese.
This in itself raises interesting questions and dilemmas – not least the fact that healthy people are already being turned down for things like health insurance based purely on their BMI. Gyms could feasibly even be contributing to the issue, helping people move out of the ‘healthy’ BMI category and into ‘overweight’ by training hard and building muscle mass. This would be a huge irony, given that these people will certainly be fitter, healthier and at lower risk of lifestyle disease as a result of being active. Meanwhile, people with high levels of dangerous visceral fat, at significant risk of lifestyle disease, are able to pass entirely under the BMI radar.
The new study will therefore be hugely valuable, both to individuals and to gyms wanting to prove their contribution to people’s health. By mapping subjects’ distribution of fat and muscle mass and overlaying this with data about lifestyle, genetics, blood sugar and cholesterol – as well as scanning brains, hearts, bones and carotid arteries – the study aims to link the distribution of excess fat, and especially abdominal fat, to risk of diseases such as diabetes, cardiovascular disease and cancer. It will, believes Matthews, give a “completely new window” onto the body.
The next step will be for the fitness sector to start mapping the body composition of its members. The latest imaging technology will be beyond most operators’ budgets, but there’s already a range of affordable devices on the market that use bio-electrical impedance analysis (BIA) to estimate body composition, and in particular body fat – an instant way to focus members on a far more important indicator for their health than their BMI.
And in the longer term? As today’s technology becomes more affordable, and the findings of the imaging study start to filter through, it’s possible to foresee a day when clubs will prescribe wellbeing programmes based on scans. Imagine how powerful it would be to map someone’s body to create a personalised wellness prescription, monitoring falling levels of abdominal fat and being able to give hard stats on how this is reducing risk of disease.
Gyms have a huge opportunity to embrace this new approach, ensuring the fitness sector becomes the bridge that connects new thinking in science with the people who can most benefit from it.
Kate Cracknell, Editor
@healthclubkate
