Body Mass Index – A Controversial Measure
When it comes to measuring body weight and assessing health risks, the body mass index (BMI) has been a popular tool for decades. However, its usefulness has been a subject of debate among health experts.
The story of body mass index begins in the early 19th century and is attributed to Belgian statistician Lambert Adolphe Jacques Quetelet. As a mathematician, Quetelet was interested in developing a tool that could be used to measure the health of populations, rather than individuals – the so called ‘average man’. He rather eloquently noticed that ‘the transverse growth of man is less than the vertical.’(Blackburn & Jacobs, 2014) Mental note: Quetelet was a mathematician, not a doctor!(Blackburn & Jacobs, 2014; Eknoyan, 2008)
In 1832, he came up with the idea of the “Quetelet Index,” a calculation that considered both height and weight as measures of body mass. In the 1970s, the World Health Organization (WHO) adopted the BMI as a standard measure for obesity and overweight. This was after Ancel Keys conducted a study using a very select (but not extremely diverse) group of ‘healthy’ body types to support the concept.(Blackburn & Jacobs, 2014)
Criticisms of the Body Mass Index
One of the criticisms of the body mass index (BMI) is that there is no physiological reason to square a person’s height in the formula. This aspect of the BMI was originally proposed by Quetelet to account for the fact that weight tends to increase faster than height, as people get taller. However, critics argue that squaring the height in the formula is arbitrary and has no scientific basis.
Another issue with the BMI is that it ignores waist size, which is a clear indicator of obesity level. Research has shown that people with a high waist-to-hip ratio are at greater risk for health problems such as heart disease and diabetes, even if their BMI falls within a normal range.
The measure can go quite skewwhiff when it comes to adolescents – growth spurts make height rather variable!(Liu & Gordon, 2013)
Alarmingly, this measure is particularly problematic in older adults. Consider this, if a person loses height due to osteoporotic vertebral compression fractures their BMI would increase! Or, as we age, we are more likely to accumulate visceral fat something the BMI does not account for. In addition, there is the condition called sarcopenia obesity. An older adult can be losing muscle mass (sarcopenia) while maintaining BMI. A practitioner may recommend weight loss methods that further worsen the loss of muscle mass simultaneously – not a good result! The patient’s functional strength deteriorates leading to greater frailty. (Cetin & Nasr, 2014)
Finally, there is the obesity paradox. Strangely, for people over 75 the likelihood of death from cardiovascular disease decreases with an increasing BMI.(Cetin & Nasr, 2014)
How can we address this? We need to take a more nuanced approach. Waist circumference is a useful additional test and is good as if not better at measuring adiposity in older adults. And if you want to implement a weight loss diet for older adults, make sure you prescribe a resistance training exercise program at the same time to maintain muscle mass.