Healthcare systems around the world should rethink how they diagnose obesity, according to an international expert group that says current approaches are too reliant on body mass index (BMI).

The global Commission on Clinical Obesity recommends focusing on measures of body fat, in addition to BMI, to avoid people being misdiagnosed.

Additionally, the Commission recommends two categories of obesity diagnosis to distinguish between obesity causing chronic disease and obesity associated with variable health risk, but not ongoing illness.

The Science Media Centre asked third-party NZ experts to comment.

Professor Lisa Te Morenga, Professor of Māori Health and Nutrition and Rutherford Discovery Fellow, comments:

“One third of New Zealand adults have a BMI of 30 or more classifying them as obese. BMI is calculated from two easy to measure variables: height and weight. On average having a high body weight relative to height is an indicator of having excess body fat and increased risk of some diseases. Its simplicity makes it a useful, affordable tool to assess health and disease risk in large population studies For example, it allows us to monitor changes in the health risk status of the population in relation to changes in factors such as the quality of the food supply, changing patterns of physical activity, or environmental pollutants.

“However, BMI was never intended to diagnose excess body fatness and risk of disease of an individual. Someone with a high weight relative to their height giving them a BMI of 30 might have lots of muscle, or carry lots of fat on their bum and thighs, neither of which confer much risk of illness. On the other hand some groups in our population (notably people of Asian and Indian descent) can carry a small amount of excess fat in high-risk places (around the vital organs) while presenting with a relatively low BMI, and therefore their increased risk of conditions such as diabetes could be missed.

“So it is a welcome advance to have this report recommending a more nuanced approach to diagnosing and supporting individuals with obesity that either puts them at increased risk of illness (pre-clinical obesity) or is present with illness (clinical obesity). The focus on obesity as a disease as opposed to a lifestyle choice is well overdue and will contribute to reducing the weight stigma experienced by people with obesity, particularly Māori and Pacific peoples. It will also enable medical professionals to be more targeted in the type of treatment delivered to these patients (i.e. needs-based treatment) thus reducing pressure on our healthcare system.”

No conflicts of interest declared.

Boyd Swinburn, Professor of Population Nutrition and Global Health, University of Auckland, comments:

“The 58 international experts involved in this Commission (importantly including people with lived experience of obesity) have done a superb job of thinking through and answering many of the really challenging questions around obesity – for example: how should Body Mass Index (BMI) be used; is obesity a disease or an illness or a risk factor for disease; when should people with obesity be considered for treatment; how to deal with weight bias and stigma?

“The Commission recommends that BMI is valuable for epidemiological studies and clinically as a screening tool. Beyond that, other measurements (such as waist and hip circumference) and assessments of organ function (such as liver, kidney, heart) are needed to be able to classify people as having obesity or not and, within the obesity group, into pre-clinical or clinical obesity depending on whether there is evidence of organ dysfunction or not. People with a very high BMI (greater than 40) are considered to have clinical obesity.

“The conversion of a continuous, imperfect single measure of BMI into a more nuanced ‘syndrome-approach’ to define more sensitive and specific categories of obesity will be great use for clinicians in deciding who to treat and for healthcare policymakers in deciding eligibility for state-funded treatment, including medications and surgery.”

No conflicts of interest.

Professor Rinki Murphy, Department of Medicine, University of Auckland; endocrinologist and clinical head of Specialist Weight Management Service, Te Mana Ki Tua, Counties Health NZ, comments:

“In the context of the longstanding debate over whether obesity is a disease or simply a risk factor for other diseases, the new definition of what constitutes clinical obesity as a disease, helps clarify this situation.

“The recommendation is to use both BMI and body fat percentage or waist circumference, (unless the BMI is clearly very high, greater than 40), and then to screen for obesity-induced organ dysfunction or loss of functional ability for conducting activities of daily living.

“This information is routinely collected by those specialising in obesity management, but this has not been used for distinguishing those with clinical obesity as a disease versus those who have pre-clinical obesity with no significant impairment. This distinction is more helpful in providing personalised health advice than the historic grading of obesity by the level of high BMI (class 1, 2, 3 etc).

“An important goal of these recommendations is to enhance access to comprehensive care and evidence-based treatments for people living with clinical obesity and to reduce weight-based bias and stigma. Currently, people receiving the extremely limited number of public-funded bariatric surgeries in New Zealand already need to fulfill the criteria for clinical obesity, and they must meet additional rationing criteria based on the severity, number and type of organs affected.

“There is currently no national public funding for any obesity medication, but perhaps defining clinical obesity as a disease entity will improve access to more effective, obesity treatment options.”

Conflict of interest statement: “Clinical head of Specialist weight management service, Te Mana Ki Tua, Counties Health NZ, Te Whatu Ora; Endocrinologist, Auckland Diabetes Centre, Te Toka Tumai, Auckland Health NZ, Te Whatu Ora; Pharmac diabetes advisory committee member; Speaking honoraria from Lilly, Novo Nordisk, Boeringer Ingelheim; Consultancy for NZ Clinical Trials”

Dr Wayne Cutfield, Professor of Paediatric Endocrinology, Liggins Institute, University of Auckland; and Starship Children’s Hospital, comments:

“The comprehensive Lancet Commission article highlights two issues:

1. BMI alone is inadequate to identify obesity. Other measures (waist circumference, DEXA determined body fat) are also required.
2. The current BMI definition of obesity risks overdiagnosis. Recategorisation into clinical obesity (obesity with obesity related diseases) and preclinical diabetes (obesity without these diseases) is recommended.

“GPs and, increasingly the general populace, use and increasingly understand BMI as a measure of adiposity. Waist circumference requires age, gender and ethnicity determined normal values and cutoffs. In New Zealand, these do not exist and would require more intricate assessment of adiposity. Yes, it would add precision, but would be more difficult to use and interpret. BMI is imperfect but is an easy tool to use and understand and usually identifies those who are overweight or obese.

“The pre-clinical obesity classification implies that this group has less of a problem that requires less management. However, the Commission doesn’t acknowledge that obesity leading to diabetes, hypertension, heart disease or cancer takes many years if not decades to develop. An individual with pre-clinical diabetes who loses weight will be further away from developing these diseases, which is a good thing.”

No conflicts of interest.

Professor Sir Collin Tukuitonga, Professor of Public Health, University of Auckland, comments:

“The Body Mass Index (BMI) is widely used as a measure of obesity globally, even though the index is an unreliable measure of body fat.

“Alternative measures, such as bioimpedance body fat measures, are impractical for clinical use.

“Several studies have shown that Polynesian people have more muscle mass than fat and cut off points have been adjusted to take account of this reality.

“Overweight and obesity are very common in Pacific Islands people and nine of the 10 nations in the Pacific are among the most obese nations on Earth. Obesity is a key driver of high rates of Type 2 Diabetes Mellitus (T2DM) in the Pacific.

“The new guidelines will improve care for people with obesity by better differentiation on obesity categories – pre-clinical obesity (minimal health risk) and clinical obesity with significant risk of complications.

“The change will help with reducing stigma and improve patient management.”

No conflicts of interest declared.

Associate Professor Roshini Peiris-John, co-Director, Centre for Asian and Ethnic Minority Health Research and Evaluation, University of Auckland, comments:

“The proposal to overhaul obesity diagnosis is timely and highly relevant to Asian populations in Aotearoa and globally.

“Based on BMI cut-off points for Asians, a recent report found obesity has doubled among Asian New Zealanders in less than a decade, from 26% to 53%. Many Asians, particularly those from the Indian subcontinent, tend to carry a proportionately higher fat mass for a given BMI than Europeans, which is not reflected in the measure of obesity used in the report, and is likely to be an underestimation of the problem.

“People of South Asian descent have a higher risk of developing weight-related health complications such as Type 2 Diabetes at lower BMI than people of European descent. The recommendation to add measures of body fat, such as waist circumference or direct fat measurement with BMI to detect obesity is highly appropriate and will help Asian people living with obesity get the care they need.

“People living with obesity are stigmatised in some Asian communities and weight bias can lead to inequalities in care for people with obesity. The Commissions call for personalised health advice and evidence-based care is highly relevant.”

No conflict of interest.

Professor Sir Jim Mann, Professor in Medicine, Co-Director Edgar Diabetes and Obesity Research Centre, comments:

“The Lancet Diabetes and Endocrinology Commission report on the ‘Definition and diagnostic criteria of clinical obesity’ has made a series of recommendations. Some are helpful in that they categorically confirm what those of us who research and practice in this field have long been saying in response to the continuing debate concerning the value of body mass index (BMI) as a measure of obesity. BMI is a useful measure of health risk at a population level and for epidemiological studies.

“However, when BMI is used as an individual measure of health, the consequences of excess adiposity should be considered in terms of total body fatness as measured, for example, by a DEXA scan or by considering the distribution of the excess fat around the body. Given that it is not feasible to undertake scans on everyone with a high BMI, in practice this means measuring waist circumference, waist-to-hip ratio or waist-to-height ratio.

“It is also good to see emphasis on the need for all people living with obesity to receive appropriate personalised health advice free of bias and stigma, which are obstacles to prevent and treat obesity.

“Likely to be more contentious is the suggestion that, despite the relationship between increasing levels of excess body fat and ill health being a continuum, there is a need to define ‘health’ and ‘ill-health’ as distinct entities. The Commission therefore suggests distinguishing ‘clinical obesity’ from ‘pre-obesity’, the former being characterized by signs and symptoms of altered organ function or inability to carry out daily activities as a result of excess body fat.

“Although the Commissioners provide cogent arguments for this approach and suggest reasonable management approaches for the two entities, as well as public health approaches to prevention, it could be argued that given the continuum of risk, the relatively arbitrary nature of BMI cut offs, and the contribution of several risk factors to health outcomes, this is not the most appropriate approach for the calculation of attributable risk to individuals or indeed to managing the epidemic proportions of obesity.

“I would also be concerned that in countries such as ours where there is considerable pressure on health budgets that the bulk of funding available for the management of obesity would be devoted to the treatment of those with ‘clinical obesity’ whereas there is much to be gained from the perspective of individuals as well as public health by intensive management of many of those in the ‘pre-obesity’ category, e.g. those with pre-diabetes. While such benefit is acknowledged in the report there is emphasis on the needs of those who are defined as clinically obese and very likely that limited funding will be directed to that group.

“Despite these reservations, I believe this to be an important document that deserves widespread discussion and indeed implementation of a national plan of action for obesity alongside the national action plan of action for diabetes, type 2 being one of the most important consequences of obesity, currently under consideration of the Government of Aotearoa.”

No conflicts of interest.