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August 14, 2013
Science is easier to believe when it coincides with our opinions. Since I would
like to eat whatever I want without worrying about my weight, I was pleased with
recent news. CTV reported: “Study finds moderately overweight people might live
longer.”
It seemed like the real thing. In January, the reputable Journal of the American
Medical Association (JAMA) published an analysis that showed that fatter people
live longer.
But it turned out to be wishful thinking. Walter Willett, chair of the nutrition
department at Harvard University’s School of Public Health in Boston was quick
to throw cold water on the report. “This study is really a pile of rubbish,” he
said unequivocally, “Anyone who believes that is just completely nuts.”
How could JAMA have got it so wrong? As is often the case, the devil is in the
details as Bonnie Liebman from the Centre for Science in the Public Interest
found out.
The problem was with what JAMA had included, not what they left out. It was a
meta-analysis; a review of 97 different studies. Smokers were included but
shouldn't have been because they tend to be thin and die younger. Their
inclusion, about 20 per cent of the study, makes overweight people look
relatively healthy.
JAMA also included sick people who, at the end of their lives, loose a lot of
weight. Again, the inclusion of thin, unhealthy people makes fat people appear
relatively healthy.
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JAMA chose to ignore cause and effect by including such distortions.
Thinness, in the case of smokers and the sick, is an effect of illness not a
cause of reduced life expectancy. Being thin doesn't cause them to die - -
being sick causes them to be thin. And being fat does not result in
increased life span.
Despite wishful thinking, excess weight remains risky. Expanding waistlines
contribute to diabetes, heart disease, cancer, stroke and death. Cancer as a
result of being overweight kills about 9,000 Canadians annually.
Still worse, sensational reports get more attention than reliable ones that
report the cold, hard truth. One underreported study by the U.S. National
Cancer Institute tracked 1.46 million people over 10 years and clearly
linked excess weight and cancer. JAMA was invited to join with their
relatively small number of 37,000 participants but they declined.
Interpretation can be tricky. JAMA wasn't factually wrong; it was misleading
in what it claimed. The results would have been useful to an insurance
company who wanted a statistical connection to weight and death for whole
populations.
So, how can you tell if a scientific study is reliable? In meta-analysis
studies, make sure the what's included or excluded doesn't distort claims.
In experiments, the double-blind model with a randomized control group is
the gold standard. The sample size should be large enough to represent whole
populations. The experiment should yield the same results each time it is
run regardless of who conducts it.
Studies that confirm what we wish were true, without investigation, are
self-deception.
David Charbonneau is the owner of Thompson Studio
He can be reached at
dcharbonneau13@shaw.ca
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