Ground Report

Surprising Diet Study Result: Red meat not the bad guy this time

By Leo Kretzner, 1/30/2010

Many a medical study is done on diet and cancer. Some search for eating patterns among groups of people who do and don’t get cancer. Or they may determine if dietary changes made within the study have measurable positive effects in people.

A new study by Dr. Erin Richman of the Harvard School of Public Health is less commonly seen: She and colleagues followed the diets of 1,294 men already diagnosed with and treated for prostate cancer, focusing on disease recurrence or progression – essentially asking ‘who came out of remission and what did they eat?’

The researchers, both at Harvard as well as colleagues at the University of California, San Francisco, found men who ate the most eggs or poultry with the skin had a two-fold greater risk for their cancers to recur or progress than men who ate the least of these.   

Prior studies have shown greater intake of saturated fat in red meat is associated with advanced prostate cancer and overall prostate cancer mortality. Others have shown that fish consumption is related to lower chances of cancer progression. Neither of those associations was found this time.

The new study followed only men who had been treated for their cancer and provisionally ‘cured’, with no detectable levels of prostate specific antigen (PSA). Patient information came from twenty-five study centers across the United States.

Men were allowed to eat whatever they wanted and were simply followed for an average of two years, answering detailed food questionnaires every six months. A patient’s cancer was judged to recur or progress if there was a consistent rise in PSA, a re-emergence of other symptoms such as urinary problems, or evidence of metastases.

The Good News

The good news was that 90% of the men had no sign of cancer progression during the course of the study. However, for those who did, there was a significant dietary association with eggs and poultry with skin.

The link to chicken or turkey specifically with the skin was teased out by looking closely at a non-statistically significant yet suggestive tendency for poultry in general to be associated with progression. When broken down to ‘usually with’ versus ‘usually without’ skin, there was a clear two-fold higher risk of progression for skin-eaters over those who preferred their bird skinless.

This association was particularly true for men whose cancer was considered higher risk to begin with, by multiple criteria including high PSA level and pathological grade. For these patients, high consumption of poultry with skin was associated with a four-fold greater incidence of cancer recurrence.

These correlations held true when researchers controlled for multiple differences between the groups, such as the type of treatments received, whether a person smoked, other items in their diets, and various socioeconomic indicators. Even adjusting for the total amount of saturated fat consumed did not diminish the association of prostate cancer progression with a diet high in eggs and poultry with skin.

The scientists speculated that carcinogens called heterocyclic amines may be involved. These compounds are known to cause mutations in DNA and are found at higher concentrations in well-done poultry than in other meats. Some previous studies have shown an association between grilled meats in general and various cancers, including prostate.

As to the association with eggs, a compound called choline may play a role. It is found in abundance in egg yolks, and although an essential nutrient in small amounts, high blood levels of it have been associated with higher risk for prostate and colon cancer. The direct involvement of choline or heterocyclic amines in this case remains speculative.

The study is online and will be in an upcoming issue of the American Journal of Clinical Nutrition, a publication of the American Society for Nutrition. (http://www.nutrition.org/ )

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Leo Kretzner is a molecular biologist and science writer in Claremont, CA.