Wading through all the ways to diagnose obesity - can we find our way to a simple common ground?

In recent years, obesity expert groups around the world have been eagerly creating guidance documents on how to reframe the diagnosis and assessment of obesity, to look beyond BMI, and embracing weight-related health issues. Unfortunately, these guidances do not align in their approaches, and can thus seem confusing to navigate.

The Lancet Commission proposes a new definition of obesity. They recommend that we should not diagnose obesity based on body mass index (BMI) alone, advising that we consider other assessments for excess body fat, including waist circumference, waist-to-hip ratio, waist-to-height ratio, and/or DEXA scans. Once obesity is confirmed, they recommend that we further classify individuals as having either clinical obesity (requiring that they meet at least one of 18 criteria for obesity-related health issues), or preclinical obesity (if they do not meet any of these 18 criteria). (see my extensive comments on this approach, blogged here).

The American Association of Clinical Endocrinologists suggests that we reframe the diagnosis of obesity to ABCD (Adiposity-Based Chronic Disease) in their 2025 consensus statement update. They advise assessment for excess adiposity including anthropometric criteria beyond BMI (including similar parameters including waist, waist-to-height, and/or DEXA scan), and to use the ABCD framework for clinical assessment and staging according to presence and severity of obesity related health complications.

Note that the ABCD staging system has actually not been validated as a differentiator or predictor of health outcomes or mortality. In contrast, the Edmonton Obesity Staging System (EOSS) is a long-established staging tool that has been validated as a predictor of all cause mortality, and has actually been proven to be a better predictor of mortality than BMI alone.

The European Association for the Study of Obesity (EASO) recommends a framework for diagnosis, staging, and management of obesity that aligns with the ABCD concept in their 2024 consensus document. They recommend that the diagnosis of obesity should include anthropometric evaluation with criteria including a BMI of 25 or greater and waist-to-height ratio of at least 0.5, or a BMI of 30 or greater; and a clinical component including medical, functional, or psychological impairments or complications. They recommend staging of obesity according to severity of clinical manifestations and complications, referring back to our Obesity Canada guidelines as to how to do this.

I, for one, feel mentally exhausted trying to bring all of these guidance documents together into a concise, easy to use framework to follow in clinical practice. As obesity is a global health condition, it would be really great if we could all align on one straightforward approach!

My suggestion? Let’s keep it simple! Our Obesity Canada definition of obesity, from our 2020 Clinical Practice Guidelines, is:

A prevalent, complex, progressive and relapsing chronic disease, characterized by abnormal or exccessive body fat (adiposity) that impairs health.

To assess for excess body fat (adiposity), one theme that is consistent across these guidance papers (and which I wholeheartedly agree with!), is to look beyond BMI to include other anthropometric assessments of excess fat tissue – particularly the central (abdominal) fat that is associated with impaired metabolic health. In fact, in our recently published 2025 Obesity Canada Pharmacotherapy Clinical Practice Guidelines (disclosure: I am the lead author), our very first recommendation is to consider measures like waist circumference, waist-to-hip ratio, and waist-to-height ratio in assessment for excess body fat and whether obesity medication is thus an appropriate treatment option for that individual. This is because BMI tells us nothing about body composition (muscle vs fat), nor where the body fat is being stored. Many people with a BMI less than established ethnicity-specific cutoffs will have excess body fat associated with metabolic health issues when you look at these central measurements, and thus should be offered appropriate weight management strategies.

BOTTOM LINE: Obesity can be quite simply defined as a prevalent, complex, progressive and relapsing chronic disease, characterized by abnormal or exccessive body fat (adiposity) that impairs health. We don’t need to make it more complicated than that. Look beyond BMI to include waist circumference, waist-to-height ratio, and/or waist-to-hip ratio, when assessing for excess adiposity.

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