Most of us are no stranger to BMI: weight in kilograms divided by height in metres.

At the population level, research tells us that a higher BMI is associated with an increased risk of certain conditions, such as type 2 diabetes and high blood pressure. Obesity rates, according to the World Health Organization, have tripled globally since 1975.

But although it is enthusiastically adopted in doctors’ rooms and also by lay people to determine their body composition, BMI is much less useful as an individual health indicator.

Australian experts, who discussed the benefit of BMI and possible alternatives at the International Conference on Obesity in Melbourne last month, say health judgments based solely on BMI can be stigmatizing and potentially harmful. They are now calling for more precise action that goes beyond just taking the number at face value.

Risks affected by race

BMI is a minus indicator of body fat. “The risks of some health conditions change as people gain weight, but BMI doesn’t tell us much about an individual’s health,” says Dr Priya Sumitran, who leads the Obesity Research Group at the University of Melbourne. “It’s hard to set a BMI limit for optimal health.”

The concept of BMI originated from Adolphe Quetelet, a 19th century Belgian astronomer and mathematician whose goal to describe “l’homme moyen” – the statistically average man – influenced the development of eugenics.

Initially called the Quetelet Index, the term BMI was coined by researchers in 1972 who described the scale as “quite unsatisfactory” but preferred “over simplicity of calculation” and “at least with the quality of any other relative weight index as an indicator of obesity.” Relativity.” Obesity as a medical issue only emerged in the West in the last century, with American life insurance companies collecting data on weight and height and correlating the information with deaths.

According to official guidelines approved by the World Health Organization, a BMI of less than 18.5 is considered underweight. A score between 18.5 and 24.9 gives a “healthy” weight, 25 to 29.9 is overweight, and a score of 30 and above is considered obese. There are several caveats to this classification, including that it is less applicable to people of tall, short, and muscular stature.

The health risks related to obesity are also affected by race. Compared to Europeans, people of Polynesian ancestry have lower levels of body fat at the same BMI. The scale also overestimates obesity in African Americans. For Asians, the health risks associated with obesity occur at a low BMI, which has led countries like Singapore to revise their guidelines to classify 23 and above as excess.

Smithran says obesity can also be defined as an excessive accumulation of fat that is a health risk. “There will be people who have a BMI above 30 but who do not have an unhealthy fat accumulation.”

Another drawback of the indicator is that it does not take into account the distribution of fat. “If the distribution is more central, if it’s around your internal organs, it will have more health consequences than the traditional pear-shaped distribution around the buttocks,” says Professor Louise Burr, president of the World Obesity Federation.

Burr, who is also chair of the Department of Child and Adolescent Health at the University of Sydney, says BMI remains a useful measure of demographic trends over time.

“We know, for example, that the percentage of people with a high BMI … has increased significantly over the past few decades than it has been, in Australia and many other high-income countries,” she says. “In South Africa, women are more likely to have a high BMI than men… In China, boys are more likely to have a high BMI than girls of the same age.”

The Lancet Committee on Clinical Obesity Diagnostic Criteria—an international panel of experts including Bohr—is evaluating the use of BMI and discussing new ways to diagnose obesity, including whether there are better measures of body composition.

You can’t evaluate nutrition by body size

Dr. Alex Craven, a bariatric surgeon at Austin Health in Melbourne, is concerned about what he sees as an over-reliance on BMI as the sole indicator of individuals’ health.

“For some reason regarding obesity, we accept that we can advise people based on a single number … to say: Your BMI is this, and therefore you are automatically unhealthy,” he says.

While BMI can be helpful, using it on its own “would be equivalent to your GP taking your heart rate…, and not looking further, giving you a diagnosis and medication based on that,” Craven says.

Calls for other measures of body composition are not new, and it is likely that the reason for BMI persistence is the simplicity of its calculation.

“The BMI is very simple: All we need is a scale and a tape measure,” Craven says. “Just because something is right, [it] It does not infer quality automatically.”

There are alternative measures, such as the waist-hip ratio, which has been found to be better predictors of cardiovascular disease (the downsides: waist measurements are difficult to take accurately, and Bohr says the ratio doesn’t work for children), and waist-to-height ratio, which may be more predictive. Better risk of death.

The Edmonton Obesity Rating Score measures the impact of obesity and takes into account conditions including diabetes, high blood pressure and osteoporosis.

“I can teach my patients to use it in less than five minutes, and I can teach junior doctors, nurses, and doctors to use it very quickly,” Craven says. “The only drawback is that you have to treat your patients with a bit of curiosity and ask questions about things that are often more important to them than their weight anyway.”

Dr Fiona Wheeler, a dietitian and lecturer at Queensland University of Technology, is frustrated that the “panic about body weight” and rising obesity rates in recent decades has led to public health messages prioritizing weight control.

“The dietary guidelines talk about weight before they talk about food,” Wheeler says. “You can’t evaluate nutrition by body size.”

A heavy focus on weight might mean, for example, overlooking genetic errors of metabolism — rare genetic disorders — that affect weight.

Wheeler’s doctoral thesis, which studied eating behavior and size acceptance, found that people who focus on a healthy lifestyle, regardless of BMI, have more nutritious diets.

“The poorest diets – the narrowest diets most likely to meet nutritional requirements – were those who focused on weight and were less concerned with health,” she says. “They also have the worst levels of body receptivity.”

Some researchers recognize that “in focusing on obesity, we are inadvertently creating an environment that may lead to unhealthy eating behaviors, or make people who live in larger bodies feel uncomfortable,” Burr says.

“There is a lot of stigma from health professionals that doesn’t help with this situation,” she says. Even if a new definition of obesity replaces BMI, Burr doesn’t think it will “magically change people’s opinions about weight stigma.”

“I think whatever word we use to describe people of large body sizes who have had health complications from that, that word will be stigmatized in time, unless we shift some thinking about it on a societal level, and on a health professional level as well.” .

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