There is a new study out that reinforces a point that I have made repeatedly, that focusing on people’s weight (as measured by the Body Mass Index) instead of their health is the wrong way to go and in fact may be harmful because it discourages people from a healthy lifestyle, despite all its benefits, if it does not result in weight loss. As one of the authors of the study says:
Given the number of papers my supervisor, Dr. Ross, and I have published on the topic, I would argue this is the biggest drawback of using BMI: it doesn’t always change even though you may be getting healthier. This is particularly so if you adopt a physically active lifestyle, along with a balanced diet, but are not necessarily cutting a whole lot of calories. This lack of change in BMI or body weight is all too often interpreted as a failure, resulting in the disappointed individual resuming their inactive lifestyle and unhealthy eating patterns.
However, as we have argued most recently in a paper in the Canadian Journal of Cardiology, several lines of evidence suggest that weight loss or changes in BMI are not absolutely necessary to observe substantial health benefit from a healthy lifestyle. Thus, an apparent resistance to weight-loss should never be a reason for stopping your healthy behaviours.
First, it is well established that increasing physical activity and associated improvement in cardiorespiratory fitness are associated with profound reductions in coronary heart disease and related mortality independent of weight or BMI. Second, exercise (even a single session) is associated with substantial reduction in several cardiometabolic risk factors (such as blood pressure, glucose tolerance, blood lipids, etc.) despite minimal or no change in body weight. Third, waist circumference and abdominal fat (arguably, the most dangerous fat) can be substantively reduced (10-20%) in response to exercise with minimal or no weight loss. In fact, significant reductions in fat mass often occur concurrent with equal increases in muscle mass in response to physical activity – equal but opposite (and beneficial!) changes which are not detected by alterations in body weight on the bathroom scale, and thus BMI.
But in this media culture that idolizes thin people and sets them up as the standard for attractiveness, this new message will have a hard time gaining acceptance, despite the fact that losing weight and keeping it off is very hard to do. People will try to do that rather than the more accessible goal of healthy eating and regular exercise, despite the greater benefits of the latter.