BMI shouldn’t be the only way to assess who can access weight-loss drugs

Around one in three Australian adults (32%) has a body-mass index (BMI) of 30 or above. A further 34% has a BMI of 25 or above.

Australia’s regulator has approved Wegovy, the weight-loss version of Ozempic (semaglutide) and Mounjaro (tirzepatide) for weight management, alongside a reduced-calorie diet and exercise.

To access these medications, adults must have a BMI of 30 or above or a BMI of 27 and a weight-related condition such as high blood pressure or sleep apnoea. The drugs aren’t subsidised on the Pharmaceutical Benefits Scheme (PBS) for weight loss, so users face still high out-of-pocket costs.

These drugs work by activating the GLP-1 receptor, which increases insulin secretion and improves the liver’s use of glucose. This decreases the user’s appetite, leaving them feeling fuller after eating less. In trials, these medications reduced participants’ body weight by up to 20% and improved their health outcomes and quality of life.

But while doctors and allied health providers are reducing their reliance on BMI to guide treatment decisions, eligibility for Wegovy and Mounjaro rely on it. This needs to change.

Your BMI alone doesn’t reflect your health status

A Belgian mathematician first invented BMI in the 1830s to try and quantify the “average man”.

An American physiologist and dietitian then adopted BMI in the 1970s to screen for obesity. It has since been used a tool to screen large populations for obesity.

BMI was never meant as the sole measure for a person’s health. When we use BMI with an individual patient, it can often overestimate the risk of their weight on their health. People have a lot of muscle mass, for example, may have a high BMI but low health risks.

BMI can also underestimate a peron’s weight-related health impacts, such as the risks for elderly people with low muscle mass.

Weight doesn’t tell us the whole story about a person’s risk for poor health. But because it’s easy to see a person’s physical shape, it’s often incorrectly used as a marker of healthiness.

It’s possible to improve your health by eating a more nutritious diet and getting more active, even if your weight doesn’t change.

For people who don’t move much during the day, increasing physical activity can boost your heart, lung and mental health.

The definition of obesity might also change

Obesity is most commonly diagnosed when a peson’s BMI is 30 or above.

But earlier this year, an international committee recommended changing how obesity is diagnosed. In its view, a person with a high amount of body fat that is having an impact on their health should be diagnosed as having obesity. So should those with a BMI over 40.

However, according to its recommendations, to diagnose obesity at lower BMIs, a health practitioner should assess the person’s waist circumference or directly measure their body fat, through a special set of scales that directly measures percentage body fat.

These measurements would be assessed according to different cut-offs for obesity based on age, gender and ethnicity.

On top of these body measurements, it also proposes a new diagnosis of “clinical obesity”. This would be given when there is evidence of organ dysfunction or obesity impacting every day function. This way of diagnosing obesity looks at overall health, and not just BMI.

The committee recommended weight-loss treatments, including medications, should be individualised and evidence-based.

What other indicators could clinicians use?

Obesity is complex, with each person experiencing it differently. So rather than basing weight-loss medication eligibility on BMI, clinicians should be able to consider the potential benefits (and risks) for an individual.

The Edmonton Obesity Staging System is a good example of a measure that uses BMI plus any other health conditions the person has, how the person moves and functions day to day, and psychological symptoms such as depression or low mood.

A higher stage is associated with poorer health outcomes, such as having organ damage, being unable to work, or having major depression. A moderate stage might include having high blood pressure, having some limitations on your daily activity and subsequent impacts on quality of life. This staging could help determine who would get the most benefit from weight-loss medicines.

A more comprehensive assessment of health using the Edmonton Obesity Staging System could help patients and their doctors have an informed discussion about the benefits and drawbacks of weight-management medications. For example, the medications could be targeted to people with higher stages rather than just relying on BMI.

This could mean people with lower BMIs, but more health conditions or difficulty with physical function, could decide to use medications, as they would be more likely to have health benefits.

Don’t overlook nutrition and exercise

While medications can help many users improve their health, they won’t be suitable or work for everyone. And not everyone will sustain the same level of weight loss, especially if they’re not supported with dietary changes and exercise.

Research trials of these medications have included the best nutrition, physical activity and psychological support for patients undergoing treatment. Weight-loss drugs should always be used in conjunction with these other supports to get the best health outcomes.

Whether you use weight-loss drugs or not, if you have weight-related health issues, you’re more likely to improve your physical function, your other health conditions and quality of life if you have support from a team of health professionals. This might include a dietitian, exercise physiologist, psychologist and care from a trusted GP.