In healthcare settings, a person living with obesity can do everything they’re “supposed” to do and still feel like they didn’t succeed.
Why? Because in obesity treatment and research, success is often measured by a single number: percent of total body weight lost.
This is the tension at the heart of a new scoping review co-authored by Obesity Canada staff and expert collaborators across Canada and internationally. The paper takes a closer look at how percent weight loss targets (like 5% or 10%) became so common in obesity research, and what we might miss when they become the main goal in clinical practice.
One number has become the measure of “success”
In obesity research and treatment, percent weight loss is often used as the primary measure to show that a treatment is working. It’s straightforward to calculate, easy to report, and makes it simpler to compare results across studies.
But a weight loss percentage can’t fully capture improvements in obesity complications, physical function, mental wellbeing, quality of life, or the day-to-day reality of living with obesity.
When percent weight loss is the primary target, it can quietly shape what we study, what we prioritize in care, and how insurance coverage is determined—sometimes outlining when support is started or stopped—regardless of what matters most to people living with obesity.
What the research set out to answer
This scoping review had two clear goals: to summarize how percent weight loss targets are used in adult obesity research, and to look at those targets alongside the health benefits they’re often linked to.
Here’s what the evidence shows about percent weight loss targets and real-world outcomes:
- Most studies aimed for similar targets
Weight loss targets for study participants were set between 3% and 10% of starting body weight. Only two studies set targets as high as 15% or 30%.
- Targets were often justified using the same landmark studies
When studies linked percent weight loss targets to health improvements, many referenced the same small set of well-resourced studies and guidelines to justify those targets, even when the newer studies used methods that looked quite different.
- Reaching the target wasn’t consistent, even with support
Results varied widely—anywhere from about 6% to 85% of participants reached the study’s target. Some studies didn’t clearly report whether the target was reached. This raises real questions about the feasibility and sustainability of these targets for most people living with obesity.
- Obesity isn’t being measured like other chronic disease targets
Most chronic diseases track progress using specific health markers like blood pressure or blood sugar numbers, not a percentage change.
Obesity is different. Body weight is a biologically-regulated outcome, and shaped by factors people can’t fully control. It’s not a simple behaviour choice. When percent weight loss is the primary target, the review argues we risk overlooking other meaningful signs of improved health.
That’s why percent weight loss doesn’t always tell the full story: health can improve with or without major weight loss.
Why this matters for people living with obesity
Percent weight loss targets can sound neutral, but it often isn’t experienced that way. When just hitting a number becomes the main goal, it can start to feel like a judgment of effort or worth. When biology pushes back (as it often does in chronic disease management), the target can become another reason to feel like they’ve failed.
If we want obesity care that reduces stigma, supports long-term health, and reflects outcomes that matter most to people, we need to widen the definition of success.The review’s conclusion is clear: widely accepted percent weight loss targets are often based on similar research, and may not be feasible or sustainable for most participants.
What could “success” in obesity treatment look like instead?
The authors point to a broader, person-centered view of progress, including things like:
- Improvement in obesity-related health conditions
- Better quality of life and mental wellbeing
- Feeling more able to move through daily life
They also point toward approaches already emerging internationally, such as quality-of-life measures, and evolving definitions of obesity.
One practical idea raised in the paper is a co-created “obesity management dashboard”, bringing together clinical measures, what research shows is realistic for a specific intervention, and the outcomes that the person living with obesity cares about most.
The takeaway
Percent weight loss can be part of the picture. But it shouldn’t be the whole picture.
A scale can’t tell you whether someone can climb stairs without pain, sleep better throughout the night, face fewer barriers in daily life, or move more confidently through the world. Those health outcomes deserve to be recognized, too.
