Avocado (Persea americana) trees belong to the laurel (Lauraceae) family. Avocados generally are considered a healthy food but their high fat content is sometimes given as a reason for limiting consumption. Avocados are a source of beta-carotene, copper, folate, mannoheptulose, vitamin B6, and various chlorophylls, as well as dietary fiber.
Avocados have antimicrobial and insecticidal properties, as well as having been shown to protect the liver, improve cholesterol, reduce inflammation, and ameliorate osteoarthritis symptoms. Avocado extract has been shown to have chemopreventive effects in human oral premalignant and malignant cells, as well as inhibiting the growth of both androgen-dependent and androgen-independent prostate cancer cell lines in the laboratory.
Breast cancer-related effects of eating avocados
Avocados are unique in their composition and multiple potential effects on health. Some high quality research regarding avocados is available, but there also exist numerous poor quality studies. Avocados and their components have been shown to have anti-cancer effects in breast cancer cells. Animal studies have tended to focus on effects of avocados on animal health. Epidemiological studies to assess the effects of avocado consumption on breast cancer risk are rare.
Cell studies show that avocado has cytotoxic properties
A number of studies have reported that constituent compounds of avocados, their leaves and their seeds (pits) are cytotoxic to breast cancer cells, preventing their proliferation. Avocados are also a fairly good source of mannoheptulose, a seven-carbon (C7) sugar which appears to have anti-cancer properties.
Animal studies focus on avocado poisoning
Investigators have seldom attempted to determine the impact of avocado on mammary tumors in animal models of breast cancer. However, they have examined other potential health effects. Avocado seed extract has been shown to reduce endometrial volume in a rat model of endometriosis, a result that was accompanied by reductions in serum levels of estradiol (E2) and progesterone.
A lipid-rich avocado seed extract was also reported to reduce mastitis in cows by counteracting staph (Staphylococcus aureus) infection in one study. However, lactating animals that gain access to avocados or their leaves in farm settings have been known to develop a type of noninfectious mastitis, with a marked decrease in milk production, and milk characterized by cheesy consistency and clots. This has been shown to be accompanied by pathological changes in the mammary gland.
In fact, avocado leaves, bark, skin and pits have been shown to be toxic to a wide variety of animals, including rabbits, goats and horses, as well as birds. Avocado poisoning can result in fatal liver and heart damage. This appears to be caused by persin, a toxin with low concentrations in avocado flesh compared to the leaves and other parts of the avocado.
Human studies are rare
Few studies have examined the possible impact of avocado consumption on breast cancer risk. A 2007 study of postmenopausal U.S. Latinas found that avocado intake was associated with higher circulating estrone (E1), a type of estrogen. Elevated estrone levels have been found to be associated with increased breast cancer risk.
In 2022, the first U.S. prospective study of the associations between avocado consumption and cancer risk in men and women was published. The authors used data concerning 45,289 men in the Health Professionals Follow-Up Study (HPFS, 1986-2016) and 67,039 women in the Nurses’ Health Study (NHS, 1986-2014). In men, consumption of at least one weekly serving of avocado was found to associated with reduced risk of total, colorectal, lung, and bladder cancer. In women, avocado consumption was associated with increased breast cancer risk. No associations were observed between avocado consumption and risk of total cancer or other site-specific cancers.
The authors were so surprised by the unfavorable breast cancer finding that they performed additional analysis using data concerning 93,230 younger women in the parallel NHSII (1991-2017). In NHSII, avocado consumption was not associated with breast cancer risk.
Avocados may influence estrogen metabolism
Avocados appear to have anti-estrogenic effects as a result of their plant sterol content. Avocado cell walls are a rich source of β-sitosterol, which binds competitively to both forms of the estrogen receptor, ERα and ERβ. As such, avocados have the potential to reduce ER+ breast cancer risk. However, avocados may influence estrogen levels through a mechanism other than ER binding and it is not clear that their effects are strictly anti-estrogenic. Avocados do not contain significant levels of phytoestrogens.
Avocados enhance effectiveness of tamoxifen
Like tamoxifen, β-sitosterol can act as a selective estrogen receptor modulator (SERM) and avocados have been shown to enhance the treatment effects of tamoxifen. In addition, avocado extract has been shown to reduce the tamoxifen-induced side effect of endometrial hyperplasia (thickening of the lining of the uterus), thereby reducing endometrial cancer risk. Avocados are a rich source of cytochrome P-450s, enzymes involved in tamoxifen metabolism and estrogen metabolism, the implications of which for breast cancer have not been established but appear to be favorable for patients in this case.
Avocado leaves, skin and pits incorporate toxic compounds
Avocado leaves, skin and pits contain toxic compounds such as persin, tetrahydropersin and various lauraceous acetogenins that can be cytotoxic to both breast cancer and normal cells. While some of these chemicals may eventually be developed into effective breast cancer treatments, it is unwise to consume significant amounts. Avocado flesh contains the lowest fractions of these compounds.
Avocado oil has some potentially unfavorable characteristics
Avocado oil is a rich source of β-sitosterol, with potential benefits in estrogen metabolism, as outlined above. The fatty acid profile of avocado oil is similar to that of olive oil, apart from the fact that avocado oil has a lower fraction of oleic acid and a higher fraction of palmitic acid, a saturated fat.
Below is a comparison between avocado oil and olive oil fat content. The average percentages of fatty acids are approximate; they depend on the cultivars and growing conditions and can vary greatly.
| Fatty acid | Avocado oil | Olive oil |
|---|---|---|
| Oleic acid | 65% | 70% |
| Palmitic acid | 21% | 14% |
| Linoleic acid | 11% | 12% |
| Linolenic acid | 2% | 1% |
| Stearic acid | 1% | 3% |
The link between dietary palmitic acid and breast cancer is not straightforward. Obesity has been shown to increase the potential for high palmitic acid intake to increase breast cancer risk. One study found that a diet high in avocado oil promoted the formation of mammary tumors in rats. We have not come across any studies that suggest that avocado oil has the potential to prevent breast cancer. Olive oil and walnut oil (another oil with chemopreventive properties) appear to be better choices.
Bottom line
Only the flesh of avocados should be consumed. Avocados should not be prepared by roasting avocado halves in their peels or skins. In addition, avocado leaves should not be used to wrap foods for grilling, baking or steaming.
Additional comments
Some people who are allergic to latex will also react to avocados. It has been estimated that up to half of people with a significant latex allergies will develop cross-reactivity to avocados.
We are aware that this is a favorite "healthy" food for many and are making an extra effort to find new studies as they become available. However, there is not much interest in the avocado among cancer researchers, so few truly relevant studies are available.
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 recent studies concerning this food and its components. For a more complete list of studies, please click on avocados.