"Nature" published an article: BMI is a flawed indicator

Reliance on BMI blinds us to the reality that it is possible to be obese at normal weight.
BMI does not measure body fat, and it also ignores some other factors that affect health, such as age, gender and race, so not all people with a high BMI have poor health or a higher risk of death.

·Because the BMI was developed based on measurements of white people, people of color "are less likely to fit within these parameters." Asians with a lower BMI are at greater risk of developing conditions such as heart disease than white people, possibly due to differences in body fat percentage and distribution.

Obesity is defined as a chronic disease by the World Health Organization (WHO). The World Health Organization uses body mass index (BMI) to assess the degree of "obesity". A BMI over 25 is overweight, and a BMI over 30 is obese.

The "2023 World Obesity Atlas" released by The World Obesity Federation predicts that in the next 12 years, 51% of the world's population, or more than 400 million people, will be overweight or obese. On August 17, "The prevalence of obesity and related complications in China: a cross-sectional real-world study of 15.8 million adults" was published in the academic journal "Diabetes, Obesity and Metabolism" (Diabetes, Obesity and Metabolism). A digital version of the "China Obesity Map": 34.8% of the 15.8 million adult subjects are overweight and 14.1% are obese. Both reports use BMI to measure "obesity."

On October 11, local time, the magazine Nature published an article online titled "Why is BMI Flawed?" The article "Why BMI is flawed — and how to redefine obesity" states that BMI cannot be used to measure the health of the body.

According to the article, body mass index (BMI) is calculated by dividing weight in kilograms by height in meters squared and has been used as an international standard for measuring healthy weight for decades. BMI stands for body fat, with higher numbers indicating a higher risk of metabolic disease and death. But BMI does not measure body fat, and it also ignores some other factors that affect health, such as age, gender and race, so not all people with a high BMI have poor health or a higher risk of death.

At a time when obesity rates are soaring around the world, more and more cutting-edge weight-loss drugs are entering the market. Experts worry that surging demand for weight-loss drugs will increase reliance on BMI as a stand-alone diagnostic tool. "When we only look at height and weight, we know nothing about an individual's health." Fatima Cody, who works at Massachusetts General Hospital and Harvard Medical School in the United States ·Fatima Cody Stanford said.

“Weight is not a good indicator of health”

In fact, the origin of BMI has little to do with health. According to the article, about 200 years ago, Adolphe Quetelet, a Belgian astronomer and mathematician who was obsessed with describing the characteristics of "ordinary people", recorded human body measurements - mainly Western European men - and found that weight was related to Roughly related to height squared. Dividing two numbers to express the relationship between weight and height is the famous Quitelet index.

In 1972, American physiologist Ancel Keys tested several height and body mass indexes and found that the Quintrey index was the best predictor of body fat thickness. He renamed it body mass index (BMI). ), and proposed that it reflected a healthy body shape better than the height and weight tables commonly used at the time.

However, "BMI is used to determine health risk," said Susan Yanovski, co-director of the Office of Obesity Research at the US National Institute of Diabetes and Digestive and Kidney Diseases. A somewhat crude metric.”

A study published in July found that overweight adults had a similar risk of death to those of a "healthy" weight. Another study found that about 30% of obese people had good cardiometabolic health, and about the same proportion of people with healthy BMIs had unhealthy cardiometabolism.

The article points out that BMI's simplicity may be why it's so popular. Sarah Nutter, a psychologist and weight stigma researcher at the University of Victoria in Canada, said: "BMI costs nothing - it's cheap and quick. But the obsession with BMI prevents us from recognizing that weight is not A good indicator of health.”

Body fat and other health factors need to be considered

Excessive fat accumulation can damage organs, increase the risk of cardiometabolic disease, and wreak havoc on mental, physical, and functional health.

But BMI cannot accurately reflect body fat. Two adults with similar BMIs may carry different amounts of fat. Older adults tend to have more fat and less muscle than younger adults, and women tend to have more body fat than men.

"The adult BMI chart does not reflect this change. The boundaries between BMI categories - which are the same in most countries that use the index to diagnose obesity - 'fall somewhere between science and arbitrary'." Prominent American private non-profit says Francisco Lopez-Jimenez, a cardiologist and obesity researcher at the Mayo Clinic, a sexual health organization.

Regardless of a person's gender, excess fat is most dangerous when it surrounds organs. This deep, visceral fat is more metabolically active than subcutaneous fat, and excess fat has been linked to insulin resistance, heart disease, and other metabolic problems. Even at a healthy body mass index, it can cause problems. "Reliance on BMI blinds us to the reality that it is possible to be obese at normal weight," Lopez-Jimenez said.

Stanford said that because the BMI was developed based on measurements of white people, people of color "are less likely to fit within these parameters." For example, Asians with a lower BMI are at greater risk for conditions such as heart disease compared with white people, likely due to differences in body fat percentage and distribution. The WHO recommends that Asians use a lower BMI to measure overweight and obesity, and some Asia-Pacific countries are practicing this.

In June this year, the American Medical Association (AMA) proposed a policy to downplay the clinical application of BMI, calling it an "imperfect measure" that has been used for "racist exclusion" and has caused "historical harm." ". The policy recommends combining other measures such as waist circumference or body composition with BMI.

Experts interviewed by Nature recommended using BMI as a screening aid, rather than a diagnostic tool, to flag people who might benefit from further testing. "BMI can determine a person's weight, but then you need to determine how healthy that person is at that particular weight," Stanford explains. Clinicians can consider cholesterol, blood sugar, and even family history and genes in their diagnosis, factors that play a role in obesity and plays a major role in related diseases.

But Stanford and others who have long studied BMI worry that health professionals don't have time for additional diagnostic steps. In a primary care diagnosis, "they only have 15 minutes to find out everything about the patient," she said.

The explosion in demand for new anti-obesity drugs makes using BMI as a diagnostic tool even more dangerous. In the United States, a person whose BMI reaches 30, or whose BMI is between 25 and 30 and has a comorbidity, can be prescribed semaglutide for weight loss. "If you only have a 15-minute appointment, you're diagnosing based on BMI instead of taking the time to see if they actually need medication," Stanford said.

In Lopez-Jimenez's experience, patients often request medication for aesthetic reasons rather than medical ones, compounding the problem.

Efforts to go beyond BMI

Over the years, there have been some efforts to define obesity using measures other than BMI.

A committee formed jointly by The Lancet Diabetes & Endocrinology and the Institute of Diabetes, Endocrinology and Obesity at King's Health Partners, London, brought together around 60 people from around the world. , an obesity expert, is examining how weight affects health by examining every major organ system. Stanford is one of them, and she estimates the full report will be released next year.

Arya Sharma, medical director at the Royal Alexandra Hospital in Canada, believes BMI may not be a good indicator of who should be prioritized for emergency care. He and others co-created a five-step system called the Edmonton Obesity Staging System (EOSS), published in 2009, that takes into account physical, mental and functional health in addition to BMI. EOSS has been included in the 2020 Canadian Clinical Guidelines for Adult Obesity, and late last year, Chile and Ireland also launched their own versions.

However, the larger effort to go beyond BMI has only just begun. "You see this system being incorporated into guidelines, but translating it into clinical practice is going to be a bigger hurdle to overcome," Stanford said.