Body Mass Index

Lord Moynihan Excerpts

Thursday 22nd April 2021 Grand Committee

[Lord Moynihan (Con)]

My Lords, the noble Lord, Lord Addington, will not be surprised if I turn to sport to assess the effectiveness of BMI as a medical guideline. Ashling O’Connor, one of the finest sports journalists of her day, wrote at the turn of the century about the need for the Ministry of Defence to take note of modern sports science after its long-held physical standards for new recruits were excluding exceptional candidates, including top rugby players. The Army’s weight limit, based on the BMI classification, was based on a calculation that divided height in metres squared by weight in kilograms. That would have discounted many Olympic gold medal winners.

Much was made at the time of the case of the two finest Olympians this country has produced. Sir Matthew Pinsent would not have been admitted to the ranks, as he weighed more than 17 stone, because, standing 6 foot 4 inches, his BMI would have been above the limit of 28. Sir Steve Redgrave—five times rowing gold medallist in an exceptionally tough endurance sport and in my opinion the finest athlete this country has ever produced—would only have sneaked in under the bar, with a BMI of 27.6. Ray Stevens, winner of a silver medal in judo in Barcelona in 1992, would definitely not have qualified at 6 foot and 15 stone, despite being able to bench press for 25 reps and run competitive half marathons. It is therefore not surprising that the English Institute of Sport discounts the outdated BMI test in favour of a more sophisticated method, such as skinfold callipers which squeeze subcutaneous tissue, and dual energy absorptiometry and body scanners measuring bone density.

Of course, we should place BMI in context, which, with slight variations over time, is your weight in pounds times 703 divided by your height in inches squared. Being based simply on height and weight, it takes no account of body fat percentage, muscle mass, bone thickness or genetic disposition to a certain frame. It assumes that everyone has the same percentage of lean tissue and fat tissue and it takes no account of those athletes who clearly have much more lean muscle mass than the average person. These facts seriously challenge the base assumptions behind the BMI formula. It exaggerates thinness in short individuals and fatness in tall and muscular individuals. The higher muscle content—in other words, lean mass—in athletes skews BMI, as lean mass is approximately 22% denser than fat tissue.

Although BMI has been adopted by the WHO as an international measure of obesity, it lacks a theoretical basis, and empirical evidence suggests that it is not valid for all populations. What can be said in its favour is that it is simple: it is a rough and ready calculation to an indirect health indicator of obesity or being overweight. I would expect the use of BMI to decline as a useful test and new measures such as the Bod Pod and hydrostatic weighing to take prominence, not least by the World Health Organization.

Having heard my noble friend Lord Addington’s speech, I have no doubt that all his points, and those made by other speakers, will be taken into consideration by the Government. I look forward to hearing from the Minister.