Worrying about your festive BMI? You may not need to

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Roula Khalaf, Editor of the FT, selects her favourite stories in this weekly newsletter.

The writer is a science commentator

The post-Christmas period is often a time for weighing things up, whether taking stock at the end of the year or preparing for the one ahead. For others, it is simply a time for weighing: stepping on the bathroom scales while reflecting mournfully on the quantity of turkey dinners, mince pies and sherries consumed.

The seasonal phenomenon of diner’s remorse might well include a panicked estimate of body mass index, calculated by dividing weight in kilogrammes by height squared (height measured in metres). The reassuring news is that some of those with a BMI above the World Health Organisation’s “healthy” range might have less to worry about than previously thought. This year, the American Medical Association declared the index an “imperfect measure” of clinical health and “misleading about the effects of body fat mass on mortality rates”. Nor, the medics asserted, should BMI alone be used to deny insurance reimbursement.

The thinning popularity of BMI reflects an expanding recognition that the measure is saddled with both scientific and historical baggage, making re-evaluation a sensible move. The index is intended to reflect adiposity, or levels of body fat, which in theory should translate neatly into risk for weight-related conditions such as heart disease and diabetes.

But the optimum range of 18.5 to 24.9 does not account for an individual’s body shape, nor differing proportions of muscle, fat and bone. It is misleadingly high, for example, for muscular athletes. It has also historically ignored non-white populations, and has its origins in a scientific preoccupation with what is normal, desirable or ideal, giving it a shady association with eugenics.

“I do think it’s time to stop using BMI on its own,” says David Stensel, a professor of exercise metabolism at Loughborough…