Sesame seeds and sesame oil have different effects on breast cancer for different women

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Sesame has varying effects on breast cancer
Sesame seeds (Sesamum indicum) are an abundant dietary source of copper and iron, and also contain significant levels of calcium, magnesium, manganese, phosphorus, selenium, zinc, and several B vitamins. Sesame seeds have antimicrobial properties and sesame oil has been shown to have antioxidant, antihypertensive, cholesterol and other lipid lowering, and plasma glucose lowering properties. Sesame seed consumption has been shown to improve bone health.
Sesame seeds also contain the lignans sesamin, sesamolin and sesamol, which have been shown to have anti-cancer properties. Sesamol has been shown to inhibit melanin synthesis in mouse melanoma cells, resulting in reduced viability and proliferation of the cells. Sesaminol glucosides have been shown to inhibit carcinogenesis of premalignant lesions of rat colon in the laboratory. One Korean study found that frequent consumption of sesame seed oil was associated with reduced risk of stomach cancer.

Breast cancer-related effects of consuming sesame seeds and sesame oil

The sesame seed lignan sesamin has been found to reduce breast tumor area in rats with hormone receptor positive (ER+/PR+) tumors. Sesame seed lignans are converted in the human intestine to the estrogen-like compounds enterolactone and enterodiol. One Swedish study found that levels of enterolactone and enterodiol in the blood that were above the median of the women studied were associated with lower risk of reduced ERα+ and ERβ- breast cancer, but not ERβ+ or other subtypes of breast cancer. A study of Chinese women found a reduction in the risk of breast cancer among women who used sesame oil for cooking compared with those who did not. Enterolactone has also been found to increase the sensitivity of breast cancer cells to radiation, thereby potentially enhancing the treatment effects of radiotherapy. Sesame seeds are also a good source of dietary selenium, which is associated with reduced risk of breast cancer.
However, there also is evidence that sesame seeds and sesame seed oil can promote breast cancer. Several studies have found that sesame seed components can stimulate the growth of estrogen-dependent (ER+) breast cancer cells. One study using a mouse model of premenopausal ER+ breast cancer to evaluate the interaction between tamoxifen and sesame seeds in the diet found that sesame seeds not only failed to inhibit human breast cancer growth, but also tended to negate the cancer inhibitory effect of tamoxifen by promoting cancer cell proliferation and decreasing apoptosis. Sesame seeds contain relatively high levels of copper, which could contribute to angiogenesis and metastasis of breast cancer, especialy in women with inflammatory breast cancer (IBC) or triple negative (ER-/PR-/HER2-) disease.
In addition, the fats found in sesame seeds have been shown to be associated with higher risk of breast cancer. Sesame seeds have a high fat content, consisting primarily of linoleic acid (approximately 44% of total), oleic acid (39%), and palmitic acid (9%). Linoleic acid, an omega-6 fatty acid, has been shown to encourage the growth of mammary tumors in mice. Note that flaxseed, to which sesame seeds are sometimes compared, contains over 55% alpha-linolenic acid (an omega-3 fatty acid), whereas sesame seeds contain less than 1%. As a result, the ratio of omega-6 to omega-3 fatty acids of flaxseed is 0.3, compared to a far less desirable 56.3 for sesame seeds.
Oleic acid has been found both to promote and to inhibit breast cancer, depending on the mixture of other fatty acids and other components of the foods in which it is found. Oleic acid has been shown to increase the bioavailability of alpha-carotene consumed concurrently, which may help explain why high raw vegetable/high olive oil dietary patterns appear to be protective against breast cancer. Note that while olive oil, which has been shown to be protective against HER2-overexpressing breast cancer, also contains a high proportion of oleic acid, the protective effect of olive oil is thought to be due to olive lignans and secoiridoids rather than oleic acid. Consumption of palmitic acid has also been found to be associated with increased breast cancer risk.

Bottom line

Those with triple negative or inflammatory breast cancer and those taking tamoxifen should avoid sesame seeds, sesame seed oil, and related foods such as tahini and halvah. Otherwise, it appears that the impact of sesame seeds and sesame seed oil on breast cancer risk depends in part on overall diet. Based on the available evidence, adding sesame seeds or sesame seed oil to an otherwise unhealthy diet low in fruits and vegetables might increase the risk of breast cancer. Similarly, substituting sesame oil for other fats in the typical American diet by using it to fry with or to make sauces is unlikely to have much positive impact on risk. On the other hand, incorporating sesame oil in a diet rich in vegetables could potentially reduce breast cancer risk by increasing the bioavailability of carotenoids and through the chemopreventive actions of sesame lignans.

Additional comments

Highly refined sesame oil is less desirable than extra-virgin or cold pressed sesame oil since refining greatly reduces the lignin content of the oil.
There is some evidence that breathing cooking oil fumes can contribute to lung cancer and that sesame oil heated to the smoking point may act as a carcinogen.
Sesame paste and sesame seed butter produced in China are subject to less stringent quality and safety standards than U.S. products and even these lower standards may not be met. One Chinese study found aflatoxin B1 in 37 of 100 sesame paste samples measured. Sesame seeds are prone to molds which produce aflatoxins, which are mutagenic, carcinogenic and teratogenic and cause immuno-suppression in humans. Aflatoxin B1 has been shown to cause liver cancer, especially in hepatitis B-positive individuals. However, note that the dark color of Chinese sesame oil is due to the fact that the seeds are roasted before processing, not because of any contamination. Cold-pressed sesame oil made from raw sesame seeds is close to colorless.
Tahini, a paste used in Near and Far East cuisine, is made of ground sesame seed kernels. Halvah is a confection made with sesame seeds and sesame seed oil that is high in fat, cholesterol and sugar.
Below are links to recent studies concerning this food. For a more complete list of studies, please click on sesame.

Selected breast cancer studies