BMI, body mass index will no longer determine obesity

Height and weight. Are these two data alone enough to determine whether a person is healthy, underweight or obese? According to the American Medical Association (AMA), no. Not anymore. Or not only. For years, many in the medical community (and outside) have denounced the index of the body mass index (BMI), which is calculated by dividing weight in kilogrammes by height in metres squared. However, the association's response came only a few days ago: before obesity is diagnosed in a clinical setting, numerous factors such as age, gender, ethnicity, genetic predisposition, metabolism, diet, physical activity, glucose and cholesterol levels, and the proportion and location of body fat must be considered. This is a belated but potentially revolutionary decision that, if implemented well, will change and expand the concept of a healthy body to include categories that have not previously been treated equally due to the exclusionary nature and strong attachment to the white, Caucasian physiognomy that has characterised BMI since its inception.

What is the BMI and what is it for?

BMI is the numerical value that has determined our health status for decades. It is simply determined by dividing the weight measured in kilogrammes by the height measured in metres squared (BMI = weight/height2). The result shows which category we fall into:

• Less than 18.5 = underweight
• 18.5 - 24.9 = normal weight
• 25 - 29.9 = overweight
• 30 and more = obese
• 40 and more = extremely obese

It is very important to emphasise that this value alone does not provide a complete and truthful statement about the physical condition of each individual, as values vary according to age and gender. Anna Maria Colao, President of the Italian Society of Endocrinology (SIE), explains: "Women in fact have more subcutaneous fat than men, which is located on the hips and thighs and is less harmful to health than abdominal fat, which tends to accumulate in the middle of the body in men," adding that using body mass index as the sole parameter "leads "to obesity being falsely overestimated in women and underestimated in men, leading to a dangerous distortion in doctors' understanding of the risk of disease and death associated with obesity." In addition, it does not provide information on the distribution of body fat, does not distinguish between fat and lean mass, and overlooks other relevant elements that describe each person's body composition, such as bone density or the proportion of water in the body. For example, an athlete can have a low body fat percentage but a high body mass index because he has muscles. This thesis has already been supported by a UCLA study from 2016, which concluded that millions of people with BMI values corresponding to overweight and obesity are actually perfectly healthy, while people with an underweight BMI have serious health problems. A new Rutgers University study, just presented at the Endocrine Society's Endo 2023 annual meeting, found that BMI misestimates fat levels 53 per cent of the time, indicating lowerlevels than are actually present. The Italian Ministry of Health has also stressed that BMI is incomplete and only approximate, since " as "an indicator for population studies, it is not capable of assessing actual body composition, just as it does not allow us to know the distribution of body fat in the individual." In addition, the ministry warns of the danger of dieting based on BMI alone. This danger is particularly prevalent among those who see BMI not only as an objective assessment of health, but also as a means to feel socially accepted. Just as one fits into a size 40, a body mass index does not equate to health or a lower risk of disease.

Why the BMI is non-inclusive and outdated

The exclusionary, inaccurate and outdated nature of BMI is rooted in the concept of this simple calculation, which originated in 1832 as an epidemiological tool to determine the percentage of prevalence of obesity on a global scale, but hides a complicated and controversial past. Its origins go back several centuries, when the Belgian mathematician and statistician Adolphe Quetelet, working on the definition of an "homme moyen"," an average man, a prototype of human perfection, concluded that "weight increases with the square of height" His studies on anthropometric growth data were based on a sample of almost exclusively white, Caucasian Europeans, far from representing the world's ethnic diversity. Although this detail was enough to cast doubt on the theory of the scholar (who was not even a doctor), in 1972 physiologist Ancel Keys and a group of his colleagues renamed the Quetelet index the body mass index and proposed it as a measure of individual body fat, mainly because it was the best, quickest, easiest and cheapest method among a number of other poor options. These qualities are the main reason why BMI has been adopted by governments around the world since the 1980s as a method of determining population health. And so it has remained, until now, when the AMA has voted to adopt a new policy that recognises its limitations as an "imperfect measure" of health, but also its "historical harms" and "use for racial exclusion" In the statement, the association also says it "recognises that differences in body shape and composition between ethnic groups, genders, and age groups are essential to consider when using BMI as a measure of obesity."

What changes as a result of the AMA decision

From now on, BMI will no longer be the only parameter to determine a person's clinical health status or obesity. The AMA recommends its use only in conjunction with a number of other factors to provide an objective clinical picture of the patient. These include genetics, heredity, metabolism, body adiposity index, body composition, relative fat mass, visceral fat assessment and waist circumference (abdominal fat has been linked to hypertension, type 2 diabetes and heart disease, for example). "This is an important change. Now we really need to be more mindful and holistic when it comes to treating patients," Dr. Cynthia Romero tells The New York Times. She is director of the M.Foscue Brock Institute for Community and Global Health at Eastern Virginia Medical School and a member of the team that has advocated for health policy changes regarding the clinical utility of BMI. As Romero points out, the new diagnostic approach will have a major impact on the lives of thousands of people and on American society, where obesity is not only a major problem but also a real economic business involving both health care and insurance companies.