Men who eat a lot of red meat and processed meats may have a higher risk of developing prostate cancer than those who limit such foods, a large study of U.S. men suggests.

Researchers at the National Cancer Institute found that among more than 175,000 men they followed for nine years, those who ate the most red and processed meats had heightened risks of developing any stage of prostate cancer, or advanced cancer in particular.

The findings, reported in the American Journal of Epidemiology, add to a conflicting body of research on meat intake and prostate cancer risk. Because studies over the years have come to different conclusions, experts generally consider the evidence linking red and processed meats to the disease to be limited and inconclusive.

These latest findings do not settle the question. But they do suggest that processed red meats and high-heat cooking methods - namely, grilling and barbecuing - may be particularly connected to prostate cancer risk, according to Dr. Rashmi Sinha and her colleagues at the NCI.

For the study, the researchers followed 175,343 U.S. men between the ages of 50 and 71 who were surveyed about their diets - including how much and what type of meat they typically ate, as well as the cooking methods they used.

The researchers used that information to estimate the levels of certain potentially cancer-promoting chemicals in the men’s diets.

Over the next nine years, 10,313 study participants developed prostate cancer and 419 died from the disease.

Overall, the researchers found, the 20 percent of men with the highest intakes of red meat, which in this study included beef and pork, were 12 percent more likely than those who consumed the least to develop prostate cancer. That’s after a range of other factors, like smoking, exercise habits and education, were taken into account.

There was a stronger connection to advanced prostate cancer - with that risk being almost one-third higher among those who ate the most red meat versus those who ate the least.

Similar findings were seen with processed meat. But when the researchers broke the men’s diet information down further, they found that red processed meats - like bacon and red-meat sausage and hot dogs - were related to higher prostate cancer risk, while white processed meats, like poultry cold cuts, were not.

When it came to cooking methods, the only one that was linked to prostate cancer was grilling/barbecuing, Sinha’s team found.

The finding is in line with the theory that meats cooked at high temperatures may be particularly linked to cancer because the cooking process produces certain chemicals - including polycyclic aromatic hydrocarbons (PAHs) and heterocyclic amines - that are known to cause cancer in animals.

Giving further support to that idea, the researchers found that higher dietary levels of a PAH called benzo-alpha-pyrene were related to a higher risk of prostate cancer. A similar pattern emerged when the investigators looked at men’s intake of nitrites and nitrates - chemicals used to preserve and flavor processed and cured meats like ham, bacon and sausage.

In the body, nitrites and nitrates can promote the production of potentially cancer-promoting chemicals called nitrosamines.

Taken together, Sinha’s team writes, the findings point to potential mechanisms by which certain meats could promote prostate cancer.

They also highlight the importance of studying the relationship between specific types of meat and prostate cancer risk, the researchers say.

Further studies, they conclude, are still needed to establish whether certain meats, and chemicals in those foods, are in fact risk factors for prostate cancer.

SOURCE: American Journal of Epidemiology, November 1, 2009.