European researchers are saying obesity could become the leading cause of cancer for Western women in the future. Here are 3 good reasons to be skeptical.
1) "Renehan and colleagues designed a model to estimate the number of cancers that could be blamed on being fat in 30 European countries. In 2002, they calculated that 70,000 cases of cancer out of about 2 million cancer cases were attributable to being overweight or obese. By 2008, the number had jumped to at least 124,000." Renehan is Andrew Renehan, of the University of Manchester, a cancer researcher who "presented his findings to a joint meeting of the European Cancer Organisation and the European Society for Medical Oncology in Berlin on Thursday."
Research presented at conferences is often at a preliminary stage and usually hasn't been scrutinised by experts in the field. Also conference abstracts rarely provide full details about methods, making it difficult to judge how well the research was conducted. For these reasons, articles based on conference abstracts should be no cause for alarm. Don't panic or rush off to your GP.
The research here might be rock-solid for all we know, but at this point, we should take a moment to remember how much we don't know. How, exactly, did they design a model for estimating how many cancers can be blamed on fat? How much of the blame does fat get, and on what basis? What do they believe caused that leap between 2002 and 2008? And perhaps most importantly, what the hell does Renehan mean when he says, "Obesity is catching up at a rate that makes it possible it could become the biggest attributable cause of cancer in women within the next decade"? Is that prediction dependent on the obesity rate continuing to rise and if so, at what rate? Or does he believe (based on the 70,000 - 124,000 jump we're currently just taking his word for) that we'll see a similar leap in the next decade, regardless of whether the population gets fatter?
Also, when you say it's "possible it could become" blah blah blah, it would be helpful if you indicated how possible you think that is. Highly plausible? Quite possible? Eh, could happen? And how much does that prediction depend on "major causes of cancer, such as smoking and hormone replacement therapy for menopausal women" continuing to "drop dramatically," which would give obesity a leg up on becoming a leading risk factor without it necessarily becoming any more of a crisis than it already ostensibly is?
2) "Renehan said that in the U.S., some studies found obesity was responsible for up to 20% of cancers." No word on whether he added that in 2007, the Journal of the American Medical Association published a study by a group from the Centers for Disease Control and Prevention and the National Cancer Institute that found obese people have a lower risk of dying from several other forms of cancer, which made the overall cancer risk among the fat population a draw. As Gina Kolata wrote in The New York Times:
[C]ontrary to expectations, the obese did not have an increased risk of dying from cancer. They were slightly more likely than people of normal weights to die of a handful of cancers that are thought to be related to excess weight - cancers of the colon, breast, esophagus, uterus, ovary, kidney and pancreas. Yet they had a lower risk of dying from other cancers, including lung cancer. In the end, the increases and decreases in cancer risks balanced out.
The fact that breast, uterine and ovarian cancer are all correlated with fatness probably accounts for the fact that Renehan's warning is specifically to Western women; sucks for us that a lot of lady cancers fall in that group. If you're fat and have a family history or other risk factors for cancers considered obesity-related, it absolutely makes good sense to be extra vigilant. (Meaning, from my perspective, watch for symptoms and get screened, since permanent weight loss is likely to fail.) But do keep in mind the "slightly more likely" part, as well as the "thought to be related." When you take those qualifiers on top of the evidence that overall "the obese did not have an increased risk of dying from cancer," it puts the alarmist headlines about fat causing cancer in a somewhat different light.
3) Even the mainstream media bothered with a bit of balance for once. Despite Renehan's dire pronouncements, cancer expert Jan Coebergh tells the AP, "It is not likely (obesity) will have as severe an effect as smoking." Which isn't to say it won't have any effect at all, of course, but trust me on this one: I have read approximately a gazillion articles about how obesity kills in the last few years, and it is incredibly rare to find one that includes an expert saying, "Nah, that's overstating it."
Also, credit where it's due, Renehan himself notes that "Just telling the population to lose weight obviously hasn't worked," so if we want to see a drop in obesity rates, "We need to find the biological mechanism to help people find other ways of tackling obesity." That's the point you almost never see in articles about the dangers of fat — that there's still not much individuals can do about it, other than watch for symptoms and get screened. (And, of course, try to eat a balanced diet and get regular exercise, which once again, are good ideas for everyone who's able but will not necessarily cause permanent weight loss.)
I'm not saying Renehan and his colleagues are wrong. Fact is, I don't know and have no way of knowing. But I am saying, as I always say, that it's irresponsible for the media to whip up panic about fat causing X,Y and Z when a closer examination of their sources reveals that the evidence supporting the headlines is far from conclusive. As White puts it:
If you've just read a health-related headline that's caused you to spit out your morning coffee ("Coffee causes cancer" usually does the trick) it's always best to follow the Blitz slogan: "Keep Calm and Carry On"... The most important rule to remember: "Don't automatically believe the headline". It is there to draw you into buying the paper and reading the story. Would you read an article called 'Coffee pretty unlikely to cause cancer, but you never know'? Probably not.
Related: "How To Read Articles About Health" – by Dr Alicia White [Bad Science]
Causes Of Death Are Linked To A Person's Weight [NYT]