As a way of measuring whether someone is a healthy weight, the Body Mass Index (BMI) has its shortcomings. It would, for instance, put Dwayne “The Rock” Johnson and many of the All Blacks into the obese category, as it doesn’t account for their musculature.
At the International Congress on Obesity in Melbourne in October 2022, a group of experts drew on a growing body of research to describe how concepts such as “ideal body weight” or “normal” BMI are overly simplistic and don’t tell you enough about the health of the person.
“The BMI measure [a mathematical formula that links weight with height] is really convenient,” says one of those experts, Australian obesity surgeon Alex Craven. “But in terms of its accuracy, it’s terrible at predicting whether people are going to get sick and die of this disease.”
Although obesity does increase the risk of metabolic health problems such as elevated blood pressure and type 2 diabetes, it is possible to have a high BMI and be completely healthy.
“People who should be left alone to live their lives are being told there is something wrong with them,” Craven says. “Because of a number, they are being labelled with a disease that is highly stigmatised.”
Where fat is distributed and the way it interacts with the body are important. So, a person might be at what the metrics say is a “normal” weight, yet still have health problems associated with excess fat, and potentially go untreated because they are not considered heavy enough to need help.
When they come to him for obesity surgery, Craven’s patients are often surprised that he is not very interested in how much they weigh. “I’m more interested in whether they have the problems caused by obesity, because then I know I can make them healthier and improve their quality of life. If obesity is having a significant impact, there’s really good evidence that surgery is going to save their life.”
The BMI metric dates back nearly 200 years to the work of Belgian mathematician Adolphe Quetelet and it became popular in the 20th century as a risk-prediction tool for insurance companies. Craven and his colleagues argue that it is overdue for change.
Instead, they use the Edmonton Obesity Staging System, a more complex five-stage classification that takes into account whether patients have metabolic disease and how serious it is, physical problems associated with weight such as osteoarthritis, and the psychological impact. “It’s been our gold standard for a while in the clinical obesity world and now we’re starting to see it being used in general practice a lot more,” says Craven. “It forces us to do the things we should probably do as doctors anyway. So, finding out what’s going on in patients’ lives; are their joints hurting; are they having trouble sleeping; what’s their blood pressure like; is their blood glucose level in the normal range?’
A focus on health rather than goal weights helps to reduce the stigma and shame associated with having a larger body. “Feeling stigmatised is one of the biggest barriers to people seeking care for obesity – not just surgical, but also diet and lifestyle interventions,” says Craven. “And it’s going to be a barrier to people trying new medications that have the potential to save a lot of lives.”
An emphasis on target weights fuels bias, promotes disorders such as binge eating, can lead to misdiagnoses and perpetuates the idea that there is something wrong with you if you are outside the range deemed normal. It is, he says, outdated. “We now understand that you’ve got a set of genes and, when you enter an obesogenic environment with those genes, the body is going to react the way it is blueprinted to do. That’s going to cause lots of things; one of them is increased body weight.
“The other thing we know is that all weight loss stops, even the weight loss I create through surgery. It’s a normal human physiological response. When we lose some weight, our body kicks in and does all the things it needs to do to keep us alive. That means stabilising, and in most cases putting a bit of weight back on. In that context, to expect people to reach a certain weight to be healthy or ideal – it’s kind of laughable.”
This story was originally published November 12, 2022
