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A steak in causing cancer?

Elizabeth M. Whelan
November 7, 2007

A recent report by the American Institute on Cancer Research (AICR) and the World Cancer Research Fund (WCRF) has a lot of red-meat-loving Americans worried. AICR's scientific advisory committee concluded that consuming red meat (including beef, lamb, and pork) is causally linked to colon cancer — and recommended we eat fewer burgers, chops and steaks — in favor of a diet comprised primarily of fruits, produce and grains.

What is a meat-lover to do? Some perspective:

• The AICR is an organization whose reason for existence is to establish links between diet and cancer. Every 10 years, it reviews the published literature about how diet and physical activity affect cancer risk. It starts that review with the assumption that a diet-cancer risk exists — and then delves into the literature to find specific studies to support those views. This is not the normal, neutral approach epidemiologists use to investigate disease causation factors.

• While some studies purporting to link meat consumption with colon cancer have found an association between this dietary factor and cancer risk, the mere fact a study shows an association between factor X and health effect Y does not mean X causes Y. Epidemiologists assess evidence on association to determine how significant it is — and how closely it resembles real causation. All cause-and-effect relationships, such as cigarette smoking and lung cancer, are associations — but not all associations rise to the level of true causation (for example, a well-publicized report linking soda consumption and esophageal cancer on the basis of one study).

There are a few criteria scientists use to assess causation. Did the cause precede the effect? How strong is the association? How consistent are the findings from study to study? Is there a "dose-response" relationship — does exposure to large amounts of the variable pose a greater risk than lower levels, as one would expect? Any assessment of the relationship of, for example, cigarette smoking and lung cancer confirms that relationship meets these and other criteria for true causation.

Where do claims about meat and cancer fall in the spectrum from association to causation? For starters, there are no strong associations — nor is there consistency from study to study. For example, with respect to colon cancer, in a pooled analysis of 14 prospective epidemiological studies (an abstract of which was presented at a 2004 meeting of the American Association of Cancer Research), the authors write "in conclusion, [our] prospective data do not support a positive association between higher red meat and fat intake and colorectal cancer."

• It must be recognized there are complexities surrounding any question of diet and cancer — and there are benefit/risk elements to be considered.

For example, one cannot evaluate "diet" as a cause of cancer without taking into account obesity and its established role in boosting the risk of both breast and colon cancer. Individuals who regularly consume a high-fat diet — including substantial servings of red meat — may be obese, and that is the most likely causal link between their diets and elevated cancer rates rather than a carcinogen in meat.

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