Does BMI still have a role? Should we treat those with ‘pre-clinical’ obesity? Experts weigh in…

The Lancet Commission made headlines earlier this year with its new definition and diagnostic criteria of clinical obesity, which downplayed the role of BMI as an individual measure of health, and set objective criteria to differentiate between obesity as a risk factor or as an illness in itself.

But will it make a meaningful difference to the way we identify and manage obesity? Three experts discuss.

Is BMI completely out?

Not quite. While BMI is useful to identify increased health risk overall at the population level, it is not a direct measure of adiposity, and does not evaluate fat distribution on the body or indicate when excess fat is causing health problems.

“For most people, a BMI over 30 is going to be associated with excessive fat, but it’s not always,” says obesity researcher John Dixon, a member of the commission, Adjunct Professor, Iverson Health Innovation Research Institute, Swinburne University of Technology, Melbourne, and Vice President of the National Association of Clinical Obesity Services.

“People who have a lot of muscle—weightlifters, athletes, for instance—can have a BMI of 31 and not have excess fat at all.”

“We also have the problem where someone with a BMI of 27 or 28 has all the classic symptoms of an excessive adipose tissue-related disease—particularly when it’s centrally located amongst the abdominal organs.”

Given these limitations, the 56-expert commission recommended that “BMI should be used only as a surrogate measure of health risk at a population level, for epidemiological studies, or for screening purposes, rather than as an individual measure of health.”

However while the commission’s focus is specifically on defining and diagnosing obesity, management is another story – and the indications for pharmacotherapy and bariatric surgery still incorporate BMI, points out Dr Teresa Girolamo, a GP and director and cofounder of Adelaide weight management clinic Re:You Health, who is also a member of the National Australian Coalition of Obesity Services, Obesity Australia and The Obesity Collective.

“In clinical practice, we do still use BMI. We can’t get rid of BMI because at the moment, the guidelines for both medications and bariatric surgery haven’t caught up with the Lancet commission – and rightly so because it only came out in January,” Dr Girolamo says.

Rather than relying solely on BMI to identify obesity, the Lancet Commission recommends using either:

• BMI plus at least one other body size measure (waist circumference, waist-to-hip ratio, or waist-to-height ratio);
• at least two body size measures (irrespective of BMI); OR
• a direct body fat measure (e.g., DEXA scan).

“We need other factors such as the waist-to-hip ratio or waist-to-height ratio to actually look at where the fat is distributed and how likely that is to be related to illness,” Professor Dixon explains.

How best to put the new recommendations into practice?

“This is not suddenly going to become a lot more complex to assess because all we need is a tape measure,” Dr Girolamo says.

“A waist circumference is a really easy tool. Being able to do that, along with height and weight, gives us much stronger criteria for making a diagnosis of obesity with these current recommendations.”

Endocrinologist and University of Sydney Associate Professor Samantha Hocking agrees that measuring waist circumference is the most practical option in clinical practice.

“Now there is one exception to this rule and that is if you calculate the body mass index and the body mass index is over 40, you can assume that excess adiposity is present and you don’t need to go on to do one of those other measures of body fatness,” Associate Professor Hocking said in a recent Healthed lecture.

“Why? When BMI is at the lower ranges, there’s much more spread in adiposity … in general every person with a BMI over 40 has excess adiposity.”

Assess for illness or physical limitations

Once you confirm excess body fat, the next step involves conducting a medical history, physical exam, and relevant investigations to assess for signs and symptoms of an adiposity-related disease or impaired day to day function.

This then leads to a diagnosis of either pre-clinical or clinical obesity.

Pre-clinical obesity

If the person has excess body fat, but no signs or symptoms of obesity-related organ dysfunction, and no limitations with daily activities, they are considered to have pre-clinical obesity.

So in other words, pre-clinical obesity is associated with future risk, but there’s no evidence of obesity-related ill health at present.

Clinical obesity

If the person has excess body fat and either signs or symptoms of obesity-related organ disfunction, or limitations of their daily activities they meet the criteria for clinical obesity.

What about psychological impact of obesity?

But while the Lancet commission has 18 categories of evidence of organ dysfunction, it leaves out the psychological impact of obesity, which the Australian Obesity Management Algorithm and others such as the Canadian Obesity Society and Edmonton Obesity Staging System do incorporate, Dr Girolamo points out.

“We commonly have patients who may not really have any other health complications, but they come in with social anxiety and social isolation,” Dr Girolamo says, adding that while it’s very difficult to untangle the relationship between weight and mental health, she believes the psychological consequences of obesity do need to be teased out, and should factor into treatment decisions.

Does the criteria change how patients are managed?

For the most part Associate Professor Hocking and Dr Girolamo both say the new definition and diagnostic criteria align quite well with existing Australian Obesity Management Algorithm, though they do mark a shift toward more holistic care.

“The focus should be on improving health,” Associate Professor Hocking says.

“So, we’re moving away from that focus on reducing the number – weight on the scales – to really thinking about the clinical problem that the patient has that gives them the definition of clinical obesity, and targeting treatment to improve those signs and symptoms— to improve that disease,” she says.

Dr Girolamo agrees, though she notes most primary care clinicians already do that. “We are used to looking at comorbidities or complications and recognising that some weight loss would help with most of those,” she says.

This is also highlighted in the RACGP’s new position statement on obesity prevention and management, released on 5 March. The College advocates a message of “‘gaining health’ by reducing adiposopathy, rather than simply ‘losing weight’, recognising that obesity is about more than body weight.”

To treat or not to treat…

At the end of the day, it’s about the individual patient sitting in front of you, Dr Girolamo adds. While the commission’s criteria helps clarify who might benefit most from treatment, it does not imply those with pre-clinical obesity should not be offered treatment.

“Of course, we would still consider treatment for those people with pre-clinical obesity, if we felt that their health was going to benefit in some way,” Dr Girolamo says.

“I’ve got an individual sitting in front of me, and I need to work out the risk benefit analysis of putting them on treatment versus just lifestyle recommendations,” Dr Girolamo says.

Take the case of someone who has excess adiposity, a BMI of 28 and type 2 diabetes, but meets the criteria for pre-clinical obesity, rather than obesity. Should we be treating their obesity?

Associate Professor Hocking says the commission acknowledges that “for a condition like diabetes, using weight reducing medication has profound benefits, and obviously yes, that person should be treated.”

Professor Dixon agrees management will depend on your findings.

“There are a group of people with preclinical obesity who, when you look at their metabolic profile, you will say ‘the risks are so high, we need to treat you, even though you don’t have obvious dysfunction’,” he says.

“If they have a strong family history of premature heart disease or of diabetes, anything where it is likely that they will develop a significant dysfunction related to obesity as they grow older, then we need to think about the behavioural changes, but also consider when they need to have pharmacotherapy or other treatments.”

Dr Girolamo says monitoring and preventative strategies are key, “so that we can help prevent the progression of preclinical to clinical obesity with things like regular monitoring, chronic disease management plans and bringing in allied health specialists.”

The new criteria can also help justify who does not need treatment, she adds.

For example, there are people who fulfill the BMI criteria for weight loss medications, but are extremely healthy, “and they haven’t got evidence of excess adiposity, because actually they’ve got a lot of muscle weight. So that group, sometimes want it for cosmetic reasons.”

“Now we’ve got a bit more evidence to say, ‘actually, congratulations, you are really healthy, despite having a higher BMI. Your waist circumference is good. You haven’t got any of those complications or evidence of organ dysfunction.’”

Bottom line

Dr Girolamo and Professor Dixon say recognising obesity as a multifactorial illness is crucial to de-stigmatising it – and improving outcomes.

“It is a chronic condition. It does justify your clinical time to get these patients back in and do proper assessments and then offer treatments, if treatment is an option for these patients,” Dr Girolamo says.

“It’s also about reducing stigma, both for patients and for the doctors, recognizing that, yes, it is a chronic health condition that we should be treating… for some individuals, it is very, very difficult because of the genetic, biological and multiple other factors that contribute to weight and obesity.”