Health workers have long relied on body mass index (BMI) to measure whether people are within a healthy weight range, but leading researchers have made the case for a new way to understand and diagnose obesity, writes Jesse Copelyn for Spotlight.
To tackle the global rise in obesity, our understanding of the condition needs to change, according to a Lancet Commission convened by 58 global experts from different medical specialties. While we have historically thought of obesity as a risk factor for other diseases like diabetes, their report, published in the journal Lancet Diabetes and Endocrinology, concludes that obesity is sometimes better thought of as a disease itself, which can directly cause severe health symptoms.
By categorising obesity as a disease, public health systems and medical aid schemes worldwide would be more likely to cover people for weight-loss drugs or weight-loss surgery, according to the report. Currently, these services are often only financed if a patient’s obesity has already led to other diseases. This is given that obesity is not viewed as a stand-alone chronic illness.
But if we’re going to redefine obesity as a disease, or at least some forms of it, we need good clinical definitions and ways to measure it. For a long time, this has posed challenges, says the Lancet report.
Perils of BMI
Health workers often rely on BMI to gauge whether a patient is within a healthy weight range – taking a person’s weight in kilograms and dividing it by their height in metres squared.
A healthy weight is typically between 18.5 and 25. Someone whose BMI is between 25 and 30 is considered overweight, while someone with a BMI of more than 30 is considered obese. But according to the Lancet report, this is a crude measure, providing very little information about whether a person is actually ill.
One basic issue is that someone can have a high BMI even if they don’t have a lot of excess fat. Instead, they may simply have a lot of muscle or bone. The report notes that some athletes are in the obese BMI range.
Even when a high BMI does indicate a person being obese, it still doesn’t tell us where a person’s fat is stored, which is vital medical information. If excess fat is stored in the stomach and chest, it poses more severe health risks than when stored in the limbs or thighs. This is because excess fat will do more harm if it surrounds vital organs.
The lead author of the Lancet report, Professor Frances Rubino, said the pitfalls of BMI have long been understood, but practitioners have continued to use it.
“BMI is still … the most used approach everywhere, even though medical organisations have [raised issues] for some time,” he told Spotlight.
“The problem is that even when we say BMI is no good, we haven’t provided an alternative. And so, inevitably, the ease of calculating BMI – and the uncertainties about alternatives – makes you default back to BMI."
To deal with this problem, the report advocates for several alternative techniques for measuring obesity which offer more precision.
The first option is to use tools that directly measure body composition, like a DEXA scanner – a sophisticated x-ray machine which can distinguish between fat, bone and muscle. It can also be used to determine where fat is concentrated. It’s thus a very precise measurement tool, but the machines are expensive, and the scans time-consuming.
Alternatively, the report recommends using BMI in combination with another measure like waist-to-hip ratio, waist-to-height ratio or simply waist circumference. If two of these alternative measures are used, then BMI can be removed from the picture.
These additional metrics are clinically useful because they provide information about where fat is stored. For instance, a larger waistline inevitably indicates a larger stomach. Studies have found that above a certain level, a larger waist circumference is linked to a higher chance of dying early, even when looking at people with the same BMI.
The report thus offers a more accurate way to measure obesity in the clinical setting, but its authors argue this is only the first step when making a diagnosis.
The second is to consider whether a patient’s obesity has actually caused health problems as this isn’t automatically the case. They acknowledge, for instance, that some obese people “appear to be able to live a relatively healthy life for many years, even a lifetime”.
The report refers to these cases as “preclinical obesity”. Such patients don’t have a disease as such, according to the report, but still have an increased risk of facing future health issues. As such, the report’s authors argue that they should be monitored and sometimes even treated, depending on factors like family history.
By contrast, cases of obesity which have directly caused health problems are referred to as “clinical obesity”. These cases should be treated immediately just like any other serious disease. It lists a series of medical symptoms associated with clinical obesity that would allow health workers to make an appropriate diagnosis.
The recommendation is thus for health workers to determine whether a person has obesity through the metrics listed above, then to determine whether it is clinical or preclinical by evaluating symptoms. This will inevitably guide the treatment plan.
How does this relate to SA?
Professor Francois Venter, who runs the Ezintsha research centre at Wits University, said the Lancet report offers a good starting point for South Africa, but must be adapted for our own needs and context.
“It’s a big step forward from BMI, which grossly under-diagnoses and over-diagnoses obesity,” he said, adding that additional metrics like waist circumference are a “welcome addition”.
The view that clinical obesity is a disease needing immediate treatment is also correct, Venter said. However, South Africa’s public health system is not in a financial position to start handing out weight-loss medicine to everyone who needs it.
But while it may not yet be feasible to treat all cases of clinical obesity in South Africa, Venter believes we should use the diagnostic model offered by the Lancet Commission to begin identifying at least some people with clinical obesity so they can start treatment.
“You have to start somewhere, and for that you need a good staging system. Let’s use the Lancet Commission… to see if we can identify and screen a few priority people and start to work on the drug delivery system.”
Yet while he believes the commission makes important contributions, he also cautions that we need more data on obesity in Africa before we can apply all of its conclusions to our own context.
“If you go to the supplement of the Lancet Commission, there’s not a single African study there. It all comes from Europe, North America and Asia. It’s not the commission’s fault but (there is a lack of data on Africa).”
This is important as findings that apply to European or Asian populations may not necessarily hold for others. Consider the following case.
As noted, the commission states that BMI is not sufficient to determine whether someone is overweight and must therefore be complemented with other measures. But if someone’s BMI is above 40 (way above the current threshold for obesity), then this can “pragmatically be assumed” without the need for further measures.
However, this may not hold in Africa, said Venter.
“The commission says if your BMI is over 40, which is very big, you can infer that this person has obesity, and they are sick and need to lose weight. I don’t know if we can say that in Africa… we often have patients who are huge, yet are very active, and when you (look at) their blood pressure and all their metabolics, they’re actually pretty healthy,” he notes. “So, I think they’re sometimes jumping to conclusions about African populations, for which we don’t have data.”
Is SA ready to move past BMI?
Another concern is that while the Lancet Commission may offer useful recommendations for advanced economies, its starting assumptions may not be as relevant for countries like South Africa.
For instance, while specialists agree BMI is a crude measure of obesity, direct measures like DEXA scans are “out of our reach economically”, said Professor Susan Goldstein, who leads PRICELESS-SA, a health economics unit at the SA Medical Research Council.
And while supplementing BMI with the other metrics like waist circumference may be doable, health experts told Spotlight that currently, healthcare workers in South Africa aren’t even measuring BMI alone.
Dr Yogan Pillay, a former deputy director-general at the National Department of Health who now runs TB and HIV delivery at the Gates Foundation, said: “I can’t tell you how few people in the public sector have their BMI monitored at all. Community health workers are supposed to go out and measure BMI, but even that’s not happening”.
Goldstein said South Africa could introduce the combination of metrics proposed by the commission, like waist circumference combined with BMI, but that it would simply require “a lot of re-education of health workers”.
Prevention vs treatment
For Goldstein, the commission is correct to regard clinical obesity as a disease needing to be treated, but we also shouldn’t view medication as the only way forward.
“We have to remember that prevention is very important. We have to focus on food control, we have to look at ultra-processed foods, and unless we do that as well (in addition to medication) we will lose this battle.”
The National Department of Health already has a strategy document for preventing obesity, but some of its recommendations have been criticised for focusing on the wrong problems. For instance, to prevent childhood obesity, it recommends reforming the Life Orientation curriculum and educating tuck shop vendors so that both students and food sellers have more information about healthy eating.
But as Spotlight previously reported, there are no recommendations to subsidise healthy foods or to increase their availability in poor areas, which several experts believe is more important than educational initiatives.
Venter also highlights the importance of obesity prevention, though he emphasises this shouldn’t be in conflict with a treatment approach – instead, we need to push for both.
“The (prevention) we need to do is fix the food supply… and the only way … is to decrease the cost of unprocessed food.” But while this may help prevent future cases obesity, it doesn’t help people who are already obese. And since such people comprise such a large share of the population, we can’t simply ignore them, he added.
“Even if you fix the entire food industry tomorrow, those people who are already obese are going to remain where they are because simply changing your diet isn’t going to do diddly squat,” he added.
Goldstein added that increasing access to treatment would also inevitably reduce the costs of “hypertension, diabetes, osteoarthritis, and a whole range of other illnesses if it’s properly managed”.
One way to advance access to medication would be for the government to negotiate reduced prices of GLP-1 drugs, she said.
Funding
A final concern that has been raised about the Lancet Commission is about its source of funding.
“I don’t know how one gets around this,” says Goldstein, “but of the 58 experts on the commission, 47 declared conflicts of interest."
The section of the commission that lists conflicts of interest spans more than 2 000 words, and includes research grants and consulting fees from companies like Novo Nordisk and Eli Lilly, which produce anti-obesity drugs.
In response, Rubino told Spotlight: “People who work in the medical profession obviously … consult, and the more expertise… the more likely they are to be asked by somebody to advise. So sometimes people have contracts to consult a company – but that doesn’t mean they necessarily make revenue if the company has better sales. You get paid fees for your services as a consultant.”
Rubino said this still has to be declared as it may result in some bias, even if it is unconscious, but “if you wanted experts with zero relationship (to companies) of any sort then you might have to wonder if there is expertise available there… the nature of any medical professional is that the more expertise they have, the more likely they have engaged in work with multiple stakeholders”.
For Venter, there is some truth to this. “It’s very difficult to find people in the obesity field who aren’t sponsored by a drug company,” he said. “Governments don’t fund research… and everyone else doesn’t fund research. Researchers go where the research is funded.”
Rubino added that while researchers on the commission may have historically received money from drug companies for separate research studies or consulting activities, none received money for their work on the commission itself.
“This commission has been working for more than four years since conception… An estimate of how many meetings we had is north of 700, and none of us has received a single penny (for doing this),” he said.
See more from MedicalBrief archives:
Obesity crisis the new ‘HIV epidemic’ for Africa
Obesity measure must go beyond BMI, suggest global experts
Waist-to-height ratio better than BMI to ID childhood obesity, study finds
Moving away from BMI as a health risk indicator
Rising global obesity presents ‘unparalleled’ health threat – Lancet report