Beef is a very good dietary source of protein, iron, zinc, copper and B-vitamins. Beef also contains conjugated linoleic acid (CLA)and stearate, both of which have been shown to induce cancer cell death, including breast cancer apoptosis. However, the potentially favorable effects of CLA and stearate appear to be overwhelmed by beef's high level of saturated fat and the carcinogenic effects of naturally-occurring beef compounds, beef additives and beef preparation methods. Diets high in beef or well done beef have been linked in multiple population studies to higher risks of leukemia and cancers of the esophagus, lung, stomach, pancreas, kidney, bladder, intestine, colon, rectum, endometrium, testis and prostate. While beef fat may be responsible for some of these results, restricting consumption to lean beef would not eliminate the increased risks of most of these cancers.
Breast cancer-related effects of eating beef
Higher red meat consumption during adolescence by women in the Nurses' Health Study II has been found to be associated with increased risk of premenopausal breast cancer in adulthood. A French population study found that increasing meat consumption was associated with increasing breast cancer risk. A UK study found that both pre- and postmenopausal women who consumed the most meat (including red meat) had the highest risk of breast cancer. A German study of women under 51 years of age also found that breast cancer risk was increased with higher consumption of red meat; women with the highest consumption quartile had an 85% elevated breast cancer risk compared to the lowest quartile. For premenopausal women, the association of meat (especially beef) intake with breast cancer risk was found to be even stronger in this study.
A study of tissue removed from healthy women undergoing breast reduction surgery found that the levels of DNA adducts (which are associated with cancer development) in the breast tissue was correlated with the women's consumption of fried meat, beef and processed meat. High intake of animal fats has been linked in several studies to increased breast density, a risk factor for breast cancer and recurrence. A study that included 52,158 postmenopausal women reported that, comparing the fifth to the first quintile, red meat, the heterocyclic amine (HCA) 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline, and dietary iron each were associated with increased risk of breast cancer. Women in the Iowa Women's Health Study who consistently ate their hamburgers, steak, and bacon very well done were found to have a 4.62 times higher risk of breast cancer than women who consumed the meats rare or medium well done. However, not all studies have found an association between meat consumption and breast cancer risk.
A number of different factors and mechanisms have been proposed to account for the findings of increased breast cancer risk associated with beef consumption:
- The U.S. beef and veal industry uses zeranol (Ralgro), a non-steroidal substance with estrogenic activity, as a growth promoter. Zeranol has been found to stimulate human breast cancer cell growth and proliferation. Other growth promoters (mostly hormones) that are routinely administered to cattle also are suspected to contribute to breast cancer risk.
- Irradiation of beef, which is widespread in the U.S., has been found to result in the formation of alkylcyclobutanones, which have been shown to have mutagenic and tumor promoting activities.
- Red meat intake has been shown reduce circulating melatonin. Melatonin protects against breast cancer in several ways, including by reducing aromatase activity within the breast, thereby reducing estrogen production.
- Bovine leukemia virus (BLV), which is estimated to infect the majority of U.S. beef herds, appears to be capable of contributing to human breast cancer risk. Most women carry BLV antibodies in their blood, indicating exposure to the virus. One 2015 study reported that women with BLV in their breast tissue were three times as likely to have breast cancer as women without BLV. Beef labelled "organic" is not necessarily BLV-free. The most likely sources of BLV exposure are raw milk and raw or rare beef, which should be avoided. This also means that ground beef mixtures should not be tasted before cooking.
- Some of the HCAs formed in very well done beef and steak, and in beef gravy, are known human carcinogens. Two of the HCAs, 2-amino-3-methylimidazo[4,5-b]pyridine and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine, have also been shown to have potent estrogenic activity, inducing activation of estrogen-regulated genes, proliferation of estrogen-dependent cells and up-regulation of progesterone receptor.
- While iron deficiency anemia obviously is to be avoided, the contribution of significant heme iron in the diet as a result of regularly consuming beef could be detrimental for some women. Iron depletion has been shown to lead to significant inhibition of breast cancer cell growth in the laboratory. Relatively high levels of iron in benign breast tissue was found in one prospective study to be associated with an increase in risk of subsequent breast cancer. Excess iron can interfere with the treatment effects of the chemotherapy drugs Adriamycin and cisplatin.
Well done or flame-broiled beef are especially to be avoided. This includes all fast-food hamburgers. Although they are traditionally used as a base for gravies and sauces, be aware that fat drippings and grill residue scrapings contain particularly high levels of HCAs and ideally should be discarded.
If beef or veal is to be consumed, it makes sense to buy organic beef to avoid irradiated and growth hormone-treated meat. However, given its high level of saturated fat, tallow (rendered beef fat) is to be avoided even if organic and sourced from grass-fed beef.
Although we do not recommend supplementation with CLA (conjugated linoleic acid), we wish to advise those who do to avoid the t10,c12-CLA isomer (referred to on some supplement labels as Trans-10, Cis-12). The t10,c12 CLA isomer was found to dramatically enhance mammary tumor development in one mouse experiment. The time by which 50% of the mice in the group developed a tumor was shortened from 267 days for mice on a control diet to 169 days for mice fed t10,c12-CLA. Choose products with only the c9,t11 isomer (Cis-9, Trans-11).
The beef industry appears to take an active interest in academic studies concerning the health benefits and drawbacks of beef. The Cattlemen's Beef Board finances some cancer-related studies, raising the question of objectivity. The tone of non-U.S. studies can appear more forthright than the constrained and cautious tone of some U.S. studies. We have not come across this problem to the same degree in any other food industry that we cover.
Below are links to recent studies concerning this food. For a more complete list of studies, please click on beef.