by Judith Curry
Epidemiologists struggle to explain a study that challenges a core belief: Fat will kill you. – William Saletan
I am a bit slow out of the gate on this one, since it is already being discussed on the previous thread, but I think this one deserves its own thread.
Fat is bad for you, right? That’s what doctors tell us. But a review of nearly 100 studies, published this week in the Journal of the American Medical Association, confirms previous indications that the story is more complex. Being overweight or even mildly obese, as measured by body mass index, doesn’t make you more likely to die than a person of normal weight. It makes you slightly less likely to die.
The interesting angle taken by the Slate article is to describe the explanations for the studies findings in an attempt to make the new data fit the old ideas:
- The difference is barely significant.
- Death risk is the wrong standard.
- Overweight is too close to obese.
- The dangers of being underweight hide the dangers of being overweight.
- Some kinds of fat are worse than others.
- Fat helps you survive some diseases.
- Fat protects you against injury.
- Muscular people inflate the survival rate of the fat group.
- Sick people depress the survival rate of the “normal” group.
- Overweight gets you more medical attention and intervention.
- Medicine has made fat less harmful.
- Overweight doesn’t mean you’re getting fat. It means you’re resisting obesity.
Slate’s summary reaction to these criticisms:
On one level, these explanations sound weak and weaselly. Dogmas, even in science, don’t surrender easily to contrary evidence. Experts who think weight gain is dangerous will find ways to reaffirm that belief, explaining away data that don’t fit it. But science, in its grudging way, does evolve.
Climate change and obesity?
So why am I talking about obesity on a climate blog? The first reason is these two articles:
- What does climate change have to do with obesity? Plenty, say some scientists
- Could climate change and the obesity epidemic be linked?
Some of the points made in these articles are
- Rising inactivity rates because of hot temperatures
- Drought-induced high prices on healthy foods
- Food insecurity promotes unhealthy food choices
(JC inserts tongue in cheek)
So, the new study runs completely counter to established obesity dogma. Epidemiologists are scrambling to counter the new study. Wouldn’t it be easier to dismiss this group of scientists as obesity deniers?
Actually, I don’t think this strategy would work for obesity in terms of public opinion, after all equating being fat with being healthy would be a convenient ‘truth.’ Hey, that extra fat on my hips and thighs indicates that I am healthy?
(JC removes tongue from cheek)
The parallel with climate change attribution is this. Attempts to find simple statistical explanations for complex phenomena can result in misleading, although statistically significant, results.
The Slate article responds to this issue:
The explanations offered today in defense of the fat-is-bad doctrine are actually modifications of it. They’re taking us beyond crude categories such as BMI, overweight, and fat. A decade from now, we’ll still believe fat is bad for you, but we’ll be far more sophisticated in what we mean by “bad” and “fat.” And the JAMA study’s critics, like its defenders, will take the credit.
So the implication is that the science of obesity epidemiology needs to take into account additional confounding factors and conduct more sophisticated analyses, and I have every confidence that the epidemiology of obesity will proceed in this direction.
On the other hand, with regards to the issue of attribution of climate change, challenges to the core belief of greenhouse gas attribution is dismissed with the charge of ‘denialism.’ Is obesity epidemiology a more challenging scientific problem than the attribution of climate variability/change?