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The Lancet medical journal’s Diabetes & Endocrinology Commission last week proposed a new definition and method for diagnosing obesity, beyond simply looking at a person’s Body Mass Index (BMI), the ratio of one’s weight and height.
An associated publication also proposed a new definition of obesity specifically for Indians, on the lines of the broader recommendations made by The Lancet.
This major development comes at a time when doctors have in their arsenal new, highly effective medicines, specifically GLP-1 receptor agonists such as Ozempic, to deal with clinical obesity.
The standard method of determining obesity across the world has thus far employed BMI cut-offs as the sole determinant.
A person with a BMI of less than 18.5 is considered to be underweight, a BMI between 18.5 and 24.9 is considered to be normal, those with BMI between 25 and 29.9 are considered to be overweight, while those with BMI over 30 are considered to be obese.
BMI is calculated by dividing a person’s body mass (weight) in kilograms by the square of their height measured in metres. For instance, a person weighing 70 kg and having a height of 1.75 cm (roughly 5 feet 9 inches) has a BMI of 22.86, which falls in the healthy range, according to the definition followed thus far.
Relying solely on BMI cut-offs leads to both over- and under-diagnosis of obesity.
People with excess body fat may not always have a BMI of more than 30. They may nonetheless suffer the health consequences of obesity. On the other hand, people with high muscle mass may have a BMI of more than 30 while being extremely healthy, and in no need of any intervention.
Then there are many people who do have excess body fat, but still maintain normal organ function. They too require minimal, if any, medical intervention.
In India, for instance, many seemingly lean people with a BMI of less than 30 have abdominal fat that can affect the functioning of various organs.
“We saw that Indians would get diabetes, hypertension, heart diseases and other consequences of obesity even at lower BMI. This is because they typically have higher body fat percentages and central obesity as compared to Western counterparts,” Dr Anoop Misra, chairman of the Fortis CDOC Hospital for Diabetes, and the only Indian on the Lancet Commission, said.
Indeed, the BMI cut-offs for obesity were adjusted for Indians in 2009. Those falling in the 23 to 24.9 range were deemed overweight, while a BMI of more than 25 was deemed to indicate obesity. This too did not, however, do away with the problems arising out of using BMI as the sole yardstick to determine obesity.
The Lancet Commission defines clinical obesity as a chronic illness that results in alteration in organ functions regardless of other conditions a person might have. “It can lead to life-altering or life-threatening complications,” the Commission states.
The new definition broadens the meaning of obesity to take into account a number of physical parameters such as height, weight, and waist circumference, as well as things such as muscle mass, and the functioning of various organs.
For a clinical obesity diagnosis, the physician will have to check for all kinds of signs and symptoms, such as breathlessness, wheezing, sleep apnoea, high triglyceride levels, metabolic dysfunctions, non-alcoholic fatty liver disease, changes in reproductive system, heart failure, chronic fatigue, and knee and joint pain, among others. They may also consider how active a person is in their day-to-day life, before arriving at a diagnosis.
Under the new definition, obesity cannot simply be self-diagnosed — it is a determination for a qualified physician to make, like other diseases and conditions.
The new definition does away with the overweight category, adding instead a category called “pre-clinical obesity” where a person has excess body fat, but no associated ongoing illness. Like the diagnosis for clinical obesity, this requires meeting multiple physical parameters, and a physician to make assessments regarding organ function.
The Commission defines preclinical obesity as a physical attribute but not an illness. It says: “In some people it might represent an earlier stage of clinical obesity, whereas in other people it can be a phenotype with lower tendency to directly affect organ function.”
Even with all the additions to the definition of obesity, body size remains a crucial factor. What has changed is that BMI is now not the sole determinant of body size, which in turn is not the sole determinant of obesity.
The Commission suggests looking at any two of the following four parameters for evaluating body size:
* BMI
* Waist circumference
* Waist-to-hip ratio
* Waist-to height ratio
Doctors may also use methods such as Dexa scan to directly measure body fat.
Although on the same lines as the Lancet Commission recommendations — Dr Misra is a common author — the Indian guidelines use the classifications of ‘stage 1’ and ‘stage 2’ obesity instead of preclinical and clinical obesity.
Moreover, “BMI has been retained as the entry-point for the diagnosis in India. This is because people are familiar with it, and it would be easier to implement,” said Dr Misra.
According to the Indian definition, a person would be deemed to have stage 1 obesity if they have a BMI of more than 23 — waist circumference and waist-to-height ratio is optional for this group — but do not have symptoms that show limitations in day to day activities, and other obesity-related chronic conditions.
For diagnosis of stage 2 obesity, a person would have to have a BMI of more than 23, meet one more physical parameter of obesity (such as waist circumference and waist-to-height ratio), and suffer from obesity-associated limitations, comorbid diseases.
For pre-clinical obesity, the Lancet Commission says that the focus has to be on risk reduction and prevention of progression to clinical obesity. This requires counselling for weight loss, and prevention of wait gain along with regular monitoring. “Lifestyle interventions such as good diet and regular exercise can suffice in this group,” Dr Misra said.
For those with clinical obesity, there will be more evidence-based, and personalised interventions. Success in dealing with obesity should be assessed by improvement in signs and symptoms associated with obesity rather than loss in weight.
“Doctors now have newer weight loss medicines that can be used for treating obesity. Weight loss surgery is available. These new guidelines help physicians select better the patients who need these interventions. Using medicines to treat a person with a high BMI but no other condition or symptoms is injudicious use of the medicine,” Dr Misra said.
