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updated 3/16/2007 8:38:44 AM ET 2007-03-16T12:38:44

A major new study analysis suggests that eating too much red meat raises the risk of breast and colorectal cancer at least for some women. This latest study alone is not enough on which to base eating decisions, but combined with other research, it provides one more reason to limit red meat to no more than 3 ounces a day.

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The newest large-scale study, the Nurses Health Study II, followed more than 90,000 pre-menopausal women for 12 years. Red meat consumption across time showed no relation to overall breast cancer risk. However, when researchers conducted an analysis of only the breast cancers fueled by the hormones estrogen and progesterone, they found a relationship with red meat consumption.

After adjusting for established risk factors, including weight, alcohol, and consumption of fruit, vegetables and dairy foods, the researchers found that women who reported eating more than one and a half servings of red meat per day had almost twice the risk of developing hormone receptorpositive cancer compared with women who reported eating three servings or less of red meat per week.

Cooking method counts
Studies suggest one reason for the increased cancer risk relates to the heterocyclic amines (HCAs) that form when red meat is cooked at high temperatures (like frying and grilling), especially well-done. In laboratory studies, HCAs bond to estrogen receptors and create estrogen-like effects. In earlier research with women past menopause, those who consistently ate hamburger, beef steak and bacon very well done thus getting high levels of HCAs --had more than four times the breast cancer risk of women who consumed these meats rare or medium done.

New research suggests that HCAs may pose more danger to some people than others. Like many carcinogens, HCAs have to be activated to be able to damage our DNA and pose cancer risk. People whose genes cause HCAs to activate quickly could be at more risk of breast cancer than those whose genes lead to slower activation, according to several early studies. Most studies have not looked at breast cancers sensitive to estrogen separately from those that are not, however, which may be important based on the Nurses Health II findings.

Although red and white meat both form HCAs when cooked at high temperatures, red meat is higher in a particular kind of easily absorbed iron, called heme iron. Laboratory studies suggest that heme iron may increase colon cancer risk by damaging the colon lining and increasing the growth of precancerous cells. Several population studies link higher heme consumption with greater colon cancer risk. Scientists say that heme iron may interact with estrogen in enhancing initial development of breast tumors.

Fat levels
The link between red meat and breast cancer may also relate to fat content. Several studies link higher fat intake with higher levels of estrogen and a substance the body can convert to estrogen. Higher saturated fat consumption seems to raise levels of insulin, a hormone that may promote development of breast cancer regardless of estrogen sensitivity.

Further research will tell us much more about whether too much of any red meat increases risk, whether risk varies with the meat’s cooking method or fat content, and whether some people’s risk is raised more than others based on age or genetics. For now, we have no data suggesting that people who want to eat red meat are at risk by eating it a few times a week. But sticking to a limit of no more than three ounces a day seems a smart move for prevention of breast cancer and reduced risks to overall health.

Nutrition Notes is provided by the American Institute for Cancer Research in Washington, D.C.

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