This week, doctors confirmed what many people have long felt: Our view of obesity is unhelpful, BMI (body mass index) is unreliable, and that needs to change.

The Lancet committee urges a "radical reform" of how obesity is diagnosed, warning that reliance on body mass index has led to both under- and over-diagnosis of obesity, which affects around 1 billion people worldwide.

But if you can't rely on BMI's simple calculation of height-to-weight ratio, how can you tell if there's something wrong with your weight?

Professor Francesco Rubino, chair of the Lancet committee that wrote the report, said BMI should be used as a "screening tool" to understand risk rather than diagnose disease.

BMI cannot determine how much body fat a person has because weight is related to your bone weight, your natural muscle mass, and how much muscle you build in the gym. Rubino says only a BMI of 40 and above definitely reflects excess fat.

Instead, clinicians can determine if someone is "clinically obese" through a blood test (looking for high cholesterol) or whether they are prediabetic and a physical exam, or they can diagnose "preclinical obesity" if there is a risk of the disease from ”: High fat content.

"Obesity is a spectrum: It's not always a disease, it can be something that people can live relatively healthy lives. At the same time, other people can have full-blown disease simply because they're obese," Rubino said.

The new approach paves the way for more research into how obesity becomes a disease by directly damaging organs, rather than causing heart disease, cancer and diabetes. The health system will also use it to manage who has access to weight loss treatments, such as ozone and bariatric surgery.

But Rubino noted that while media coverage has largely focused on the idea of ​​overdiagnosis of obesity, there is also an issue of underdiagnosis, particularly in individuals with lower muscle mass.

The BMI measure, which is based on average European height and weight, works less well for certain ethnic groups, particularly Asians, because it tends to underestimate how obese they are. "Over time, I've seen that some racial groups find it more difficult to have surgery. That creates inequities and, unfortunately, obesity is already associated with obesity and compounds the problem," Rubino said.

One particular risk factor is where the fat accumulates—especially the abdomen. You can measure your waist circumference, but Rubino says that should be done by a clinician. People with a higher body mass index shouldn't worry too much about having strong limbs rather than belly fat, he said.

The report has sparked discussion about whether you can be "obese and healthy," although Dr. Andrew Jenkinson, a bariatric surgeon and author of Why We Eat (Too Much), believes this is an unhelpful term.

"You have a high body mass index and are healthy, but if your fat percentage is high, you're unlikely to be very healthy," he says. "I wouldn't say anyone with severe central obesity is metabolically healthy - their future risk is much higher than someone without abdominal fat."

He said if your BMI is above 25 and you have a normal to slim body type, your BMI may be higher due to muscle mass without having to go to the gym regularly because some people are "genetically large".

Jenkinson said it was important to take a non-judgmental approach to obesity given that two-thirds of the risk of obesity is hereditary and a Western dietary environment is a major contributor, including snacking, processed foods, lack of sleep and stress. and sedentary lifestyle. He often sees patients struggling with their weight, who are unhelpful by the advice they receive from nutritionists about caloric restriction, which trains their metabolism to store fat.

Dr Olly Williams, who studies weight stigma at King's College London, said the Lancet work would "create more certainty about the limitations of using body mass index and weight alone to measure health", although he was concerned about "preclinical obesity" ” terms can affect health. ” unhelpfully implies that illness is inevitable.

Williams studied the relationship between obesity and identity and found that people who were defined by body mass index as obese felt stigmatized and that the term failed to capture those who worked hard to control their weight through diet and exercise and those who did not. differences between people.

"There's an assumption that if you're classified as obese, you're lazy, stupid or irresponsible," he said. "For many doctors, it's a neutral term, but that's not how the public uses the term. It's very emotive and often pejorative."

He added that people with a healthy body mass index or who appear slim may have poor physical or mental health and may smoke or severely restrict calories to lose weight. He said cultural links between weight, health and morality also contributed to high rates of eating disorders, while body mass index could prevent people, especially women, from strength training.

Williams points out that in Japan, where obesity levels are low, five measures are used to determine the ill-health effects of excess fat, rather than one measure — and the responsibility for weight control lies at a "structural, systemic level." understanding, rather than emphasizing weight management. “Personal willpower and behavior change” in the UK.