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Why Food Science is So Bad (And So Often Wrong) Graphic
This week the World Health Organization put processed meat on the list of 478 other things that could cause cancer.

Eating an extra 50 grams of processed meat each day will increase a man's risk of colon cancer by 18 percent from baseline risk over a ten year period.

That said, your risk of getting colon cancer is small, but if you eat 50 grams of processed meat every day, it may increase a bit.

However, the WHO article, which appeared in the British Medical Journal Lancet Oncology elevates processed meats - like bacon and hot dogs to the same carcinogen threat level as tobacco.

Of course, the headline you read this morning probably said something like "Meat Causes Cancer" because leaving out the "processed meat" and the other niggling bits of detail makes for a boring story. Red meat was considered, but the WHO working group was unable to make a link between red meat and cancer.
"Chance, bias and confounding could not be ruled out with the same degree of confidence for the data on red meat consumption, since no clear association was seen in several of the high quality studies." 
Despite that, WHO still listed red meat as "probable" even though they couldn't find clear evidence.

It's worth putting these risks in perspective. The strongest evidence that the IARC uncovered focused on one type of cancer — colorectal — and the risks related mainly to heavy meat consumption. Still, the panel did find that a person's cancer risk "increases with the amount of meat consumed." So if you're eating five hot dogs a day, there's a lot more to worry about than if you have a steak a month. - VOX

That is, of course, just one of the problems with the near daily inundation of reporting we get on nutrition and diet. The research is often poor, biased or stretched to draw the conclusions we wish to draw based on the mood of the moment. We grasp at straws to make conclusions.

The WHO's rulings on carcinogens will likely carry more weight than most nutritional research that makes headlines, but the evidence is still problematic.  That's because studies on dietary changes are difficult. You can either look backwards at self reported or cultural dietary differences. Or you can set up a true double blind controlled study -- which is tricky because it is food. It tastes different.

As the UpShot column in the New York Times explains.
"Almost everything we know is based on small, flawed studies. The conclusions that can be drawn from them are limited, but often oversold by researchers and the news media. This is true not only for the newer work we see, but also the older research that forms the basis of much of what we already believe to be true."
Remember when we thought eat fat made us fat and clogged our arteries? For 30 years we were told that fat was what was wrong with our diets -- so we made fat free products -- replacing the fat with sugar to help it sell. Only to find that there was never much of a connection between eating fat and getting fat at all. Gary Taube's famous piece "What If It's All Been A Big Fat Lie" is a case study in the different factors tugging at what and how we eat.

As Taubes wrote more than a decade ago:
"Scientists are still arguing about fat, despite a century of research, because the regulation of appetite and weight in the human body happens to be almost inconceivably complex, and the experimental tools we have to study it are still remarkably inadequate. This combination leaves researchers in an awkward position. To study the entire physiological system involves feeding real food to real human subjects for months or years on end, which is prohibitively expensive, ethically questionable (if you're trying to measure the effects of foods that might cause heart disease) and virtually impossible to do in any kind of rigorously controlled scientific manner. But if researchers seek to study something less costly and more controllable, they end up studying experimental situations so oversimplified that their results may have nothing to do with reality. This then leads to a research literature so vast that it's possible to find at least some published research to support virtually any theory. The result is a balkanized community -- ''splintered, very opinionated and in many instances, intransigent,'' says Kurt Isselbacher, a former chairman of the Food and Nutrition Board of the National Academy of Science -- in which researchers seem easily convinced that their preconceived notions are correct and thoroughly uninterested in testing any other hypotheses but their own."
This leads to confusing contradictions in what is healthy and not healthy, what is good for you and what will kill you. It takes little in the way of scientific rigor to get on the Good Morning America show with the latest finding.

Yet one week of media blitz based on a small, flawed study could lead to years of misleading information and dozens of diet books as follow up research fails to attain the same level of sensationalism. As the UpShot notes:
"Although it's easy to point fingers and make a case that there are huge gaps in our evidence when it comes to food, it should be kept in mind that it's incredibly hard to do this kind of work. The reason we have to rely on small, poorly designed trials is because that's often all we can get. Because of this, we will probably continue to see results from mostly small, sometimes-flawed, short term studies of nutrients and additives. Treat the results of that research with the respect they deserve, but ignore the grandiose proclamations." 
Required Reading:

Vox has the best coverage with links to critics of the WHO Working Group's conclusions. Wonkblog at the Washington Post puts the issue into the larger perspective of politics and culture.

The WHO's New Warnings About Bacon and Cancer, Explained Vox

Hot, Dogs Bacon and other Processed Meats Cause Cancer, WHO Declares Wonkblog at Washington Post

Gizmodo Does a Good Job explaining Why You Shouldn't Panic

What If It's All Been A Big Fat Lie? Gary Taubes classic

Red Meat is Not The Enemy and
Unexpected Honey Study Shows Woes or Nutritional Research

How Red Meat Joined 478 Other Things That Can Cause Cancer

Carcinogenicity of Consumption of Red and Processed Meat

Scientific Criticism of the WHO report.

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