Body weight targets are based on inaccurate and outdated science; potentially harmful

Media release

Body weight targets based on inaccurate and outdated science are harming patients, experts warn

·        Judgements based solely on weight metrics like BMI, and unrealistic weight goals, can unintentionally lead to poorer health outcomes, say experts.

·        Instead, experts call for patient-centred goal setting in obesity treatment.

Embargo: 2301H UK time Tuesday 18 October

Body weight targets that stigmatise and potentially harm patients continue to be commonly used in everyday clinical practice, but are outdated and long overdue for change, argue obesity experts, patient advocates and clinical ethicists in a seminar at this year’s International Congress on Obesity (Melbourne, 18-22 October) (the biennial congress of the World Obesity Federation).

Dr Alex Craven, an obesity surgeon from Austin Health in Melbourne, Australia and colleagues draw on existing research to describe how concepts such as ‘ideal body weight’ or ‘normal’ body mass index (BMI) are overly simplistic and don’t tell you about the health of a person.

“These constructs suggest there are distinct categories of underweight, ideal, overweight and obese, with sharp boundaries that hinge on a decimal place”, says Dr Craven.

In reality, the link between body weight and health is more complex, he explains: “As a disease, obesity has many outcomes. Increased body weight is only one outcome, and it’s not the most important.”

Body weight is not the best predictor of ill health

Having a higher body weight increases the risk of developing diseases such as type 2 diabetes and high blood pressure, but it’s not a simple relationship.

"You could be categorised as ‘normal weight’ by BMI but have health problems associated with excess fat, or you could be categorised as having ‘obesity’ and have no health problems”, says Dr Priya Sumithran, Head of Obesity Medicine at Austin Health, Australia. “The problem with using weight metrics alone to set treatment goals is that they put too much emphasis on a target weight and that can be misleading.”

Evidence suggests that the risk of developing metabolic diseases like type 2 diabetes, heart disease, and stroke is much more complicated than just having excess weight. For instance, where fat is distributed, and the way it interacts with the body, are critically important.

At the same time, the pressure to achieve and maintain unrealistic body weight goals can have substantial psychological and social impact on individuals, and prioritises weight-based outcomes over health. On top of this, declaring “a normal weight range” can fuel weight bias and stigma, demotivate patients and promote eating disorders such as binge eating.

Patient-centred goal setting in obesity treatment

The goals and perceived success of obesity treatments, (like surgery, medications and lifestyle interventions), are often linked to body weight targets based on ‘ideal’ or ‘normal’ body weight. It is important that health professionals go beyond this outdated and inaccurate approach to ensure they are making patient-centred recommendations, say the authors.

The seminar highlights that when it comes to treating obesity, the amount of weight lost, and its impact on health outcomes, is much more important than the patient’s final weight.

“Outcomes like controlling obesity-related diseases, improving physical function, and better mental health are not only important to patients” says Andrew Wilson, an advocate for people with a lived experience of obesity from the Weight Issues Network in Australia. “They are also linked to medically important outcomes like life expectancy and quality of life. Focusing on these is good for everyone.”

Professor Louise Baur, President of the World Obesity Federation and Chair of Child & Adolescent Health, University of Sydney, NSW, Australia, comments: “Body mass index is a practical screening tool that can be used in assessing people with obesity.  While it’s simple and cheap for doctors and other health professionals to use, it must be used in conjunction with good clinical assessment that looks at whether physical and psychological health complications are present.”