When Science Challenges the Story: What Katherine Flegal’s Research Teaches Us About Weight and Health

Written by Vania Phitidis
Peaceful Eating Coach
Last updated on 14 November 2025

This week I received an email from Lucy Aphramor – who is an incredible human – dietitian, food and body justice warrior, and poet among other attributes. In it, Lucy reminded me of an article I’d been thinking about a week or two ago and wondering where I’d filed it as I wanted to reread it. It was a piece by Katherine Flegal, senior (now retired) scientist and epidemiologist at the Centers for Disease Control in the US. The article The obesity wars and the education of a researcher: A personal account, is Katherine’s account of the huge backlash and attempt to discredit her research on the relationship between weight and mortality, because it questioned the accepted narrative (and hence previous research). I thought I’d write about it because I think this story is important, and while I do not wish to add fuel to the fire of mistrust in science, it serves as a reminder that science is not independent of humans and our biases.

⚠️ A note before we begin:

In this piece I use terms like “normal weight,” “overweight,” and “obesity.” These are the categories used in the research I’m referencing. They come from the Body Mass Index (BMI) system – a measure that has been widely criticised for its limitations and for the way it pathologises body size. I use these words only to reflect the research as it was conducted, not to endorse them as meaningful descriptions of health or worth.

The study that shook things up

In 2005, epidemiologist Dr. Katherine Flegal, a senior researcher at the U.S. Centers for Disease Control and Prevention, published a paper that surprised almost everyone. Her study found that people in the “overweight” BMI range actually had slightly lower mortality than those in the “normal weight” range – and that even mild “obesity” carried much less risk of early death than previously believed (Flegal, Graubard, Williamson & Gail, 2005).

It wasn’t the result anyone expected, and it certainly wasn’t the result many public health leaders wanted. The reaction was fierce: media campaigns, professional attacks, even efforts to discredit her publicly. Her research was criticised not because it was sloppy – it was extremely rigorous – but because it didn’t fit the story that had already taken hold: that thinner is always healthier, and higher weight is inherently dangerous.

What happened next

Over time, other studies replicated her findings. In 2013, a massive meta-analysis led again by Flegal – combining data from nearly 3 million people – confirmed the same pattern (Flegal, Kit, Orpana & Graubard, 2013). And further research has continued to show that mortality risk is not as tightly tied to BMI as we’ve been led to believe.

But here’s the important thing: the science didn’t “disprove” that weight and health can be related. It showed that the relationship is far more complex – influenced by things like social stigma, access to care, lifestyle habits, and the quality of the data we use to measure health.

What this tells us about research

Science is a human process. It’s not a single truth, but an ongoing conversation – one that’s shaped by the culture and assumptions of the people doing it. Sometimes, when new evidence challenges a deeply held belief, it’s uncomfortable.

But that discomfort isn’t a sign that science is broken. It’s a sign that science is alive – that it grows, questions, revises, and refines.

Just as we’re learning to meet our bodies with curiosity instead of judgement, we can meet science that way too.

And for those who might be worrying…

If you live in a larger body, it’s easy to hear about “risk” and feel fear – as though your body is a ticking time bomb. Please know this: your health and longevity are influenced by many factors, not just size.

A 2012 study by Matheson, King and Everett looked at over 11,000 adults and found that when people, regardless of body size, practised just four health-promoting behaviours –

• not smoking,
• drinking alcohol within national guidelines,
• eating five servings of fruit and vegetables a day, and
• engaging in moderate physical activity about three times a week

the differences in mortality almost disappeared across BMI groups (Matheson, King & Everett, 2012).

In other words, the things that help us live longer and feel better are not the number on the scale, but the small, sustainable behaviours that nourish our bodies and support our lives.

A gentler takeaway

The story of Katherine Flegal’s research isn’t a reason to distrust science – it’s an invitation to see it with clearer eyes. It reminds us that even well-intentioned scientists can be influenced by cultural narratives about weight, and that challenging those narratives takes courage.

And it reminds us that your body is not the problem. The problem is often the stories we’ve been told about what makes a body valuable, healthy, or deserving.

Real science – and real health – are both at their best when guided by humility, curiosity, and care.

References

• Flegal, K. M., Graubard, B. I., Williamson, D. F., & Gail, M. H. (2005). Excess deaths associated with underweight, overweight, and obesity. JAMA, 293(15), 1861–1867.
• Flegal, K. M., Kit, B. K., Orpana, H., & Graubard, B. I. (2013). Association of all-cause mortality with overweight and obesity using standard body mass index categories: A systematic review and meta-analysis. JAMA, 309(1), 71–82.
• Flegal, K. M. (2021). The obesity wars and the education of a researcher: A personal account. Progress in Cardiovascular Diseases, 64, 1–6.
• Matheson, E. M., King, D. E., & Everett, C. J. (2012). Healthy lifestyle habits and mortality in overweight and obese individuals. Journal of the American Board of Family Medicine, 25(1), 9–15.