Late last year, the cancer agency of the World Health Organization classified “red meat as probably carcinogenic to humans, based on limited evidence.” In the same report, the agency said it found “sufficient evidence in humans that the consumption of processed meat causes colorectal cancer.” Damn.
Wondering what to do with all the steaks, burgers, and beef jerky you have at home? While the agency found some risk, there was no edict to avoid either red meat or processed meat entirely. The reason is that not all risks are equal -- consider that the WHO’s cancer agency categorizes shift work and sunlight as “probable” carcinogens, the same as red meat. It lumps hot dogs, bologna, and other processed meats in with alcohol and plutonium as “definite” causes of cancer. But what's WHO basing this determination on, and is there any leeway when it comes to these guidelines?
The man who singled out red meat
Red meat has long been suspect, and the argument that it could kill you started with a scientist named Ancel Keys. As a physiologist at the University of Minnesota in the 1950s, Keys noticed that American businessmen, who had the luxury of eating whatever they wanted -- omnivores of affluence, you could say -- suffered high rates of coronary heart disease. Simultaneously, Europeans were still rebuilding infrastructure after the war and had fewer food choices, but better heart health.
To find the reasons for the discrepancy, Keys launched what would become the Seven Countries Study. He and his team of researchers dispatched themselves to select destinations in Europe, Japan, and North America. They asked men in those locales what they were eating, measured serum cholesterol in their blood, and noted rates of disease.
Causation or correlation?
Keys and company found that men in Italy and Greece had lower cholesterol, seemed to drop dead less often, and said they ate less red meat than their American counterparts. Keys extrapolated his anti-meat message from there, and his crusade landed him on the cover of TIME.
Despite the great publicity, Keys had found an interesting fact pattern but nothing more. Even amateur scientists know that correlation is not causation.
Men in Italy and Greece had less coronary heart disease than American men -- they also had less use for the English language. Doesn’t mean speaking English causes heart disease. In most scientific experiments, observational studies lead to hypotheses, along the lines of “meat may cause coronary heart disease,” and then the real work begins. To test a hypothesis, researchers design a randomized, controlled study and complete it. And this is where the advice on meat falters.
Why not just conduct a study to determine causation?
Because it's impossible! “That study, even with any amount of money, in many instances is simply not possible to do,” Dr. Walter Willett, chair of nutrition at the Harvard School of Public Health, told the LA Times. “Most people don't want to stay on any prescribed diet, particularly if they're living in an environment where other people around them are eating other things.” Since you would essentially have to ask large groups of people to either abstain from or eat lots of meat for most of their lives, all with potential long-term health consequences, the practical and moral complications are pretty obvious.
Absent a bomb-proof study, Dr. Willett and his colleagues relied on observational data for their widely cited paper that repeats the advice not to eat meat. Examining statistical links between meat consumption and cause of death, they found that people who eat meat tended to die younger. They also found that these people “tended to weigh more, exercise less, smoke tobacco more and drink more alcohol than healthier people in the study.”
Good Calories, Bad Calories author Gary Taubes had a field day with this on his blog. “Every time in the past that these researchers had claimed that an association observed in their observational trials was a causal relationship, and that causal relationship had then been tested in experiment, the experiment had failed to confirm the causal interpretation -- i.e., the folks from Harvard got it wrong," Taubes wrote. “Not most times, but every time. No exception.”
Those low-carb, high-fat diets might ALSO work
OK, so there's no way to PROVE causation, but there's some pretty strong correlation going on here. Is there any hope for red meat?
Well, Stanford University designed a $2 million study to compare 300 people eating four different diets over the course of one year. The researchers found the Atkins diet, a very low-carb affair that includes dishes like "Beef Filet with Bacon and Gorgonzola Butter," was more beneficial for a person’s health than any of the high-carb, low-fat alternatives including the Ornish diet, which allows zero meat and zero cholesterol. The Atkins dieters, the Stanford team reported, “had larger decreases in body mass index, triglycerides, and blood pressure."
Lower body mass index? A good sign for anyone who wants to shed extra pounds. And the triglycerides and blood pressure? Yep, you got it. They’re both indicators of good heart health.
What to make of it all
Health studies are a tricky business. While the Stanford study sheds light on cause and effect, it only offers one year’s worth of data on 300 people. The observational studies from Keys, Dr. Willets, and even the WHO point to statistical links, but can’t rule out other reasons for the data or establish for certain that one action leads to another reaction.
At the end of the day, and at every meal, the choice to eat or avoid meat is yours, and yours alone. The studies can only tell you so much.