Experts are calling for a big change in the way we measure obesity

Traditional concepts of obesity may undergo a radical change. In a new report released this week, a widely supported group of scientists is calling for major changes to the way obesity is diagnosed and classified.

Over 50 obesity experts from around the world produced the report as part of a panel supported by The lancet. Among other recommendations, the group calls for body mass index (BMI) to be removed as the sole criterion for diagnosing obesity. They also argue that obesity should be categorized into two different types based on how much harm a person’s condition is likely to cause them.

The specific goal of the committee was to establish objective but nuanced criteria for diagnosing obesity. Obesity is currently diagnosed strictly by a person’s BMI, which is calculated based on a person’s weight and height. People with a BMI over 30 are considered obese, with severe obesity considered to have a BMI over 40 (some parts of the world use lower BMI cutoffs to account for population differences in the average size of residents).

Although BMI is an easily obtained and trackable measurement, however, it often fails to convey the whole picture, panel experts say — a criticism that many other public health experts have expressed in the past. Obesity-related harm is primarily caused by excess body fat, and sometimes BMI may fail to adequately correlate with this. A very healthy person may have a high BMI but low body fat, for example, while someone with a so-called “normal” BMI may carry a risky amount of body fat. The distribution of excess body fat can also differ from person to person, as can the health risks associated with that fat. Too much fat around a person’s waist or around vital internal organs such as the liver and heart is more dangerous than excess body fat in the skin under the arms or legs, for example.

Experts are not calling for doctors to completely abandon BMI as a tool to diagnose obesity, but rather to use it in conjunction with other body measurements. These include measuring people’s waist circumference, their waist-to-hip ratio, or their waist-to-height ratio. Medical professionals should use at least two measurements of body size to diagnose people suspected of having obesity, the researchers say, and one measurement other than BMI. Alternatively, doctors may instead collect a direct measurement of a person’s body fat, such as by conducting a bone density test known as a DEXA scan. People with a very high BMI (above 40) may still be considered to have excess body fat, they added.

“If applicable – people with obesity (BMI near or above or above obesity) should have at least one other measure of body size (eg waist circumference in most cases or DEXA if available) to confirm accurate detection of excess body fat – this would confirm that a person is indeed obese and not just, for example, a muscular person with a high BMI,” Francesco Rubino, an obesity researcher at Kings College London and chair of commission, Gizmodo said in an email.

Rubino and his committee also recommend that doctors group obesity into two broad categories: preclinical and clinical obesity. High body fat alone may not negatively affect your health, experts note, so they created a list of criteria (18 for adults, 13 for children) to identify when someone’s obesity is likely causing other body problems. Someone who has obstructive sleep apnea, severe knee pain, or poor cardiovascular health suspected to be related to excess body fat will be classified as clinically obese, for example, while someone obese but without signs of abnormal organ function will be classified as having preclinical obesity.

“Reframing the clinical effect of obesity is warranted to explain how obesity can be both a risk factor for other diseases and a direct cause of disease. The definition of clinical obesity therefore addresses a gap in the characterization of obesity as a direct cause of ill health and may be an effective way to address widespread misconceptions and biases that misguide decision-making among patients, health professionals and policy makers,” the authors write in his report, published Tuesday at The Lancet Diabetes & Endocrinology.

People with preclinical obesity may still be at higher risk for future health problems, but the distinction allows for more personalized obesity care, Rubino says. While clinically obese people should be treated immediately with effective weight loss treatments, which may include newer drugs such as semaglutide (the active ingredient in Ozempic and Wegovy) or bariatric surgery, doctors may use a less invasive approach with someone who has preclinical obesity, depending on the level of risk.

“These strategies can be as simple as offering timed monitoring and lifestyle changes aimed at feasible weight loss for people whose risk is low (even moderate weight loss can go a long way in preventing disease , associated with obesity), or include more active forms of intervention if the risk is judged to be particularly high (due to factors other than obesity itself, such as family history, abdominal fat distribution, other conditions, extreme weight, and especially the combination of the above), Rubino said.

The group’s recommendations end up being just that. But their conclusions have been widely endorsed by health-related organizations around the world – 76 in total, including the American Heart Association in the US, the Royal College of Physicians in the UK and the World Obesity Federation. Important big questions still remain to be answered about the nature of obesity, such as the exact prevalence of preclinical to clinical obesity (by the current definition of BMI alone, more than 1 billion people worldwide are estimated to be obese). But according to report co-author Robert Eckel, an endocrinologist at the University of Colorado School of Medicine, the new guidelines should greatly help both doctors and people living with obesity.

“The intent of our work was to optimize and individualize patient diagnosis and risk versus care,” he told Gizmodo. “We think this feature will benefit patients, healthcare providers and healthcare to follow.”