Beef, especially beef liver, is a rich dietary source of choline, CoQ10, copper, iron, vitamin B6, vitamin B12, and zinc. Fatty cuts of beef are an abundant source of arachidonic acid. Beef is also a very good source of selenium and a good source of thiamin. In addition, beef is an excellent source of both conjugated linoleic acid (CLA) and stearate.
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, testes and prostate. While beef fat may be responsible for some of these results, restricting consumption to lean beef would not eliminate all of the increased risks of these cancers.

Breast cancer-related effects of eating beef

The potentially beneficial effects of the CLA and stearate in beef appear to be overwhelmed by its cancer-promoting characteristics. These include beef's unfavorable fat profile and the carcinogenic effects of some naturally-occurring beef compounds, as well as the harmful effects of certain beef additives, likely infection with bovine leukemia virus (BLV), and common beef preparation methods. One 2022 study reported that dietary CLA from ruminant sources was associated with increased breast cancer risk.

Human studies

Beef and red meat intake linked to breast cancer risk
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 reported 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 determined 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 intake (especially beef) with breast cancer risk was found to be even stronger in this study. However, not all studies have found an association between beef consumption and breast cancer risk.
Meat consumption linked to DNA damage in breast tissue
A study of tissue removed from healthy women undergoing breast reduction surgery found that the levels of DNA adducts in the breast tissue was correlated with the women's consumption of fried meat, beef and processed meat. DNA adducts form when DNA bonds to a chemical mutagen and are considered the initiating event in chemical carcinogenesis.
Well-done beef linked to breast cancer risk
Several studies have reported that women with high intake of well-done beef (including barbequed meat) have a higher risk of breast cancer than those with low intake. For example, 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.
Cooking beef until well done produces carcinogenic heterocyclic amines (HCAs); the total HCA content in meat cooked until well done is approximately 3.5 times higher than that of the same meat prepared to medium-rare doneness. A study that included 52,158 postmenopausal women reported that, comparing the fifth to the first quintile, red meat, HCAs and dietary iron each were associated with increased risk of breast cancer.
Animal fat intake linked to increased breast density
High intake of animal fats has been linked in several studies to increased breast density, a risk factor for breast cancer and recurrence.

Beef growth promoters can be estrogenic

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. Some other growth promoters (mostly hormones) that are routinely administered to cattle also are suspected to contribute to breast cancer risk.

Red meat intake may reduce circulating melatonin

Red meat intake has been shown reduce circulating melatonin. Melatonin protects against ER+ breast cancer by reducing aromatase activity within the breast, thereby decreasing estrogen production. Melatonin has also been found to reduce triple negative breast cancer growth, proliferation and migration (movement to a new location) in cell and animal studies. In addition, melatonin has been shown to reduce the cardiotoxicity associated with Adriamycin(doxorubicin) chemotherapy.

Bovine leukemia virus has been linked to breast cancer

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, although not all studies are in agreement. Most women carry BLV antibodies in their blood, indicating exposure to the virus. One 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.

High levels of iron can promote breast cancer

While it is important to avoid iron deficiency anemia, the contribution of excess heme iron in the diet as a result of regularly consuming beef (especially liver) could be detrimental for some women. 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.
Tumors are iron consumers. Breast cancer cells have abnormal pathways of iron acquisition, storage and regulation, suggesting that reprogramming of iron metabolism is an important aspect of cancer cell survival. Iron has been shown to facilitate cancer cell proliferation and growth. It is also an important contributor to tumor angiogenesis (the growth of new blood vessels).
The addition of iron to breast cancer cells and their microenvironment has been demonstrated to protect them from being killed by natural killer cells. At the same time, iron depletion has been shown to lead to significant inhibition of breast cancer cell growth in the laboratory.
In addition, excess iron has been shown to have the potential to interfere with the treatment effects of the chemotherapy drugs Adriamycin and cisplatin.

Excess copper may promote metastasis

Calf's liver (veal liver) and beef liver contain especially high levels of copper. One 2024 study found that relatively high levels of copper in the urine of girls were associated with increased breast density two years post-menarche. On the other hand, other studies have reported that copper does not appear to increase breast cancer risk significantly. However, it does appear to increase the risk of recurrence. Copper has been shown to promote angiogenesis and metastasis, especially in aggressive forms of breast cancer such as inflammatory (IBC), triple negative (ER-/PR-/HER2-), and HER2 overexpressing (HER2+) breast cancer.
Although copper is a vital nutrient, breast cancer patients and survivors should not exceed the RDA (recommended dietary allowance) of approximately 0.9 mg. Pan-fried beef liver contains approximately 16.4 mg copper per four oz. serving; beef skirt steak contains about 0.11 mg.

Arachidonic acid can promote breast cancer

Arachidonic acid is an omega-6 fatty acid found in beef. Generally speaking, beef with visible fat has a higher arachidonic acid content than lean cuts. Several studies have demonstrated that arachidonic acid promotes breast cancer. For example, arachidonic acid has been shown to induce the migration and invasion of triple negative breast cancer cells. Note that grass-fed beef contains approximately half the level of arachidonic acid as grain-fed beef.

Canned meat can be source of BPA exposure

Canned meat (e.g., canned corned beef) can be a significant source of exposure to the breast carcinogen bisphenol A (BPA), an endocrine disruptor. BPA appears to be associated with increased risk of breast cancer and its progression. BPA that has leached from food packaging and containers is the main source of exposure.

Additional comments

Well-done, flame-broiled or BBQ beef especially are to be avoided. This includes 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 grass-fed organic beef to obtain a more favorable fatty acid profile and avoid growth hormone-treated meat. This will also eliminate irradiated beef, which appears to be safe, but about which concerns have been raised by some researchers concerning the alkylcyclobutanones that are generated during irradiation. Given its high level of saturated fat, tallow (rendered beef fat) is to be avoided even if organic and sourced from grass-fed beef. Angus beef has high amounts of marbling (i.e., fat) and is not organic or grass fed unless so labeled.
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.

Sources of information provided in this webpage

The information above, which is updated continually as new research becomes available, has been developed based solely on the results of academic studies. Clicking on any of the underlined terms will take you to its tag or webpage, which contain more extensive information.
Below are links to 20 recent studies concerning this food and its components. For a more complete list of studies, please click on beef.