Careful measurement of body fat can help treat obesity
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Rethinking the way we define obesity could help millions of people around the world, says a group of researchers who want to introduce a new category of “preclinical” obesity.
The current definition of obesity, by the World Health Organization (WHO), is having too much body fat that poses a health risk. The WHO recommends that health workers assess whether people are obese by their body mass index (BMI), a measure of weight for height. A BMI between 18.5 and 24.9 is considered healthy, and a lower or higher BMI indicates underweight or overweight. A BMI over 30 indicates that someone is obese.
It is true that high levels of body fat can cause infiltration of organs such as the liver and pancreas, impairing their function. It can also increase inflammation, increasing the risk of conditions such as cancer, liver disease and heart problems.
But BMI misrepresents a person’s body fat level. “With BMI, we don’t know if that ‘overweight’ is due to excess body fat or stronger muscle mass or bone mass,” he says. Francesco Rubino at King’s College London, who led a review on obesity.
Even when properly assessed, through waist measurement or, rarely, an X-ray scan, body fat levels do not fully determine a person’s health. “No two people respond the same way to excess fat. A person’s race and ethnicity, age, what foods they eat and genetics all play a role in this,” he says. Steven Heymsfield at Louisiana State University.
Therefore, Rubino and his colleagues want to add more nuances to the definition of obesity, dividing cases into preclinical and clinical cases. Both forms would be characterized by having too much body fat, but only the clinical form would have symptoms caused by excess fat, such as breathing difficulties, heart problems or difficulties in carrying out daily activities. Meanwhile, preclinical obesity increases the risk of eventually developing obesity-related symptoms, Rubino says.
It would be similar to how people might have prediabetes, where blood sugar levels are higher than usual, but not high enough to be diagnosed with full-blown type 2 diabetes, Rubino says.
Under the proposed changes, healthcare workers would directly measure people’s body fat levels using waist circumference or X-rays in addition to calculating BMI, although someone with a BMI over 40 would always be considered overweight. They would then use blood tests to assess the health of their organs and ask people if they are experiencing symptoms. Blood tests are routinely performed by many clinicians, says Heymsfield, but direct body fat measurements would increase their workload somewhat.
If widely adopted by doctors, the new definitions could mean people are offered advice and treatments better suited to their bodies, Rubino says. In general, those with preclinical obesity will only need to monitor their health and make lifestyle changes, while those with the clinical form require treatment with drugs or surgery, Rubino says.
“It would allow us to match people to the right care,” he says Adrian Brown at University College London.
Laura Gray The University of Sheffield, UK, also welcomes the proposed changes. “It is very necessary. These guidelines implement what current research says for clinical practice,” he says. “Not everyone who is obese by BMI is unhealthy, and not everyone who has a lower BMI is unhealthy.”
The updated definitions, which have already been adopted by 76 health organizations around the world, may also help reduce the stigma around the disease. “The hope is that defining obesity in a more nuanced way will show that it is a disease. It’s not just a result of behavioral things, there are many risk factors, environmental, psychological and genetic,” says Gray.
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