The genesis of the hypothesis that meat consumption may contribute to an increased cancer risk dates to the 1960s, when studies correlated the intake of animal fat within a population to cancer, specifically breast and colorectal cancers, Alexander said.

Even though it lacked scientific consensus, this "animal fat hypothesis" evolved into an "animal protein or meat hypothesis," he said.

Despite important improvements in research and statistical methodology, a better understanding of the biological factors in carcinogenesis (cancer development) and an abundance of data from hundreds of studies, Alexander said a lack of "a clear scientific consensus regarding meat consumption and cancer remains today."

The Exponent report discusses epidemiologic science and summarizes current studies.

One in 100 items

Efforts to understand and prevent cancer are important since cancer is the second-leading cause of death in the U.S. behind only heart disease, and approximately one of every three Americans will be diagnosed with a form of cancer in her or his lifetime, Alexander noted.

The specific etiology (cause or causes) of the majority of cancers remains unknown, although researchers have concluded that cancer is multifactorial, involving a complex interaction of genetic, infectious, environmental and lifestyle factors that normally take many years or decades to progress, he explained.

Identifying etiology in nutritional epidemiologic studies is even more difficult, he said.

In considering data from nutritional studies, red meat and processed meat have been commonly linked to certain kinds of cancer, including colorectal, esophageal, lung and stomach cancers, Alexander said. However, across these studies, the Exponent team determined that:

• Most associations are weak in magnitude;
• Most associations are not statistically significant;
• Many associations are null and inverse;
• Definition s of red meat and processed meat are mixed across all studies;

Alex ander said epidemiologic evidence overall does not suggest an association between red and processed meat consumption and common kinds of cancer, including breast and prostate cancers (the two most common types), as well as bladder, kidney and skin cancers and non-Hodgkin's lymphoma.

Other evidence, albeit sparse, does not suggest an association to other kinds of cancer, he said.

It also should be noted, he said, that meat's role is commonly evaluated as part of a large number of dietary foods, i.e., more than 100 food items, and if meat is not implicated in a study, researchers don't normally report this as it would be a null association and would focus instead on foods that were positively or inversely associated with the outcome.

Over time, Alexander said, several assumed mechanisms have been suggested as to how or why consumption of red and processed meats may contribute to carcinogenesis, including "dietary mutagens" -- chemical compounds that are not naturally present in meat but develop during cooking and/or preservation, such as nitrates and nitrites that are used in processed meats for preservation, color and flavor.

However, the role these chemicals play in carcinogenesis "is unclear ... as exposure is not specific to processed meats," he said, and in fact, "greater exposure may occur" from consumption of other dietary foods such as cereals and vegetables.

Researchers also have suggested that iron - specifically heme iron - may play a role, Alexander said, but although red meat is a major source of heme iron, few epidemiologic studies have investigated this factor in cancer risk, and in studies that have, associations were inconsistent.

Here's the point

DIET, as it relates to chronic diseases, including cancer, is an ever-expanding area of research, and epidemiologic studies to determine if a particular beverage or food might be associated with a particular disease are complicated since diets involve many foods and because other factors aside from diets - from family history to lifestyle choices such as exercise or smoking - may be as responsible for carcinogenesis as the food item.

That's the message of a major review of epidemiologic studies regarding the association between eating red and processed meats and cancer, which found that most associations drawn have been so statistically insignificant and weak that the associations are simply unfounded.

It's an example of why consumers and other parties need to be careful in accepting studies that associate food with disease, which is well documented in the review.

A copy of the report, which contains charts and other graphics, is available from the National Cattlemen's Beef Assn. for $30 by calling (303) 368-3138, and downloadable chapters will be posted soon at www.porkandhealth. org .

Additional information on the healthfulness and safety of food produced by America's farmers is available at www.FeedstuffsFoodLink.com .