In Saudi Arabia, the rate of breast cancer ranges from three to eight confirmed cases for every 1000 patients. Breast cancer accounts for 14.8% of all cancers reported in Saudi nationals and about 29% of cancers among females of all ages . It is incredibly important to assess the dietary factors associated with breast cancer in the Mecca region. This study showed that consuming healthy foods including black tea, coffee, fruits and vegetables, fish and seafood, legumes, and dairy products can be preventative factors against breast cancer.
Our study results showed that consuming one to five servings of dairy products daily, a major source of vitamin D for Saudi women, had up to a 96% preventative effect against breast cancer. Dairy products in Saudi Arabia are fortified with vitamin D which has been shown to reduce the risk of breast cancer by multiple mechanisms: either by promoting cell differentiation, decreasing cancer cell growth, stimulating cell death (apoptosis), or by reducing the formation of blood vessels in the tumor (angiogenesis) [15, 16]. A recent review study supports our study findings that vitamin D had an inverse relationship with breast cancer . A descriptive study conducted in Saudi Arabia by AlFaris et al. , in contrast, demonstrated results comparing vitamin D and breast cancer that did not support our findings. This result can be explained by vitamin D deficiency among both the control group and the cancer group. The study also showed a relationship between symptoms of vitamin D deficiency and breast density, where women with mild to moderate breast density appeared to develop more deficiency symptoms.
Dairy products are also a good source of calcium, which plays a role in reducing the risk of breast cancer. Although the exact mechanism is still unclear, a meta-analysis of eleven studies by Hidayat et al.  showed a connection between calcium intake and breast cancer. Calcium's ability to regulate the cells’ apoptosis, proliferation, and differentiation makes it a significant preventative factor. Both calcium and vitamin D were found to have anticarcinogenic effects in a review study by Cui . On the other hand, a recent meta-analysis published in 2019 by Chen and his colleagues on the relationship between breast cancer and milk/yogurt intake did not support our results . This discrepancy may be due to the number of servings consumed by the subjects of Chen et al.’s study  and the amount of vitamin D added to the dairy products. Some studies have indicated that environmental pollutants, growth factors, and the amount and type of fat in milk can raise the risk of breast cancer. Another relevant question is whether the cows producing the milk were given bovine growth hormone, which results in an increase in the insulin-like factor-1 in the milk and therefore causes malignant cells to proliferate .
Conjugated linoleic acid (CLA) in dairy products is considered a chemoprotective agent. CLA also has antioxidant and anti-inflammatory effects that can decrease the risk of developing breast cancer . Research on the mechanism of CLA in reducing the risk of developing breast cancer is remarkably diverse, as described in a meta-analysis conducted by Zhou et al.  Another study by McCann et al.  did not support a clear correlation between CLA consumption and the development of breast cancer in pre- and postmenopausal women. They explained their result as being due to the high level of CLA consumption necessary for a preventative effect, as compared to the relatively low consumption by a typical test subject. Aro et al.  in their study found that breast cancer risk was higher in postmenopausal women who consumed a low amount of CLA from dairy products, but not in pre-menopausal women who consumed the same amount of CLA.
The study results also showed that the consumption of one to two servings of legumes per week had a negative association with breast cancer incidence. Various phytochemicals in legumes have an inhibitory effect on cell proliferation. Xu and Chang  comprehensively studied the effect of antioxidants and phytochemicals from different common types of legumes against nine different types of cancer including breast cancer, and they found that legumes are an outstanding source of natural antioxidants for the reduction of oxidative stress and cancer prevention. The fiber content in legumes was additionally found to inhibit the enterohepatic circulation of estrogen, leading to reduction of the circulating estrogen level and resulting in a reduction of breast cancer risk . Fiber is also associated with decreasing cell mutation by binding with bile acid which is thought to promote cell proliferation .
Fruits and vegetables are rich sources of fibers that are known to protect against breast cancer. Women who have a daily intake of three to five servings of fruits and vegetables are 83.9% less likely to develop breast cancer. An important study by Farvid et al.  concluded that high fiber intake from fruits and vegetables reduced the risk of developing breast cancer in women. Antioxidants in fruits and vegetables have been shown to neutralize free radicals and prevent DNA damage that might lead to cancer . Additionally, Naja et al.  concluded that the consumption of both fruits and vegetables reduces breast cancer risk. Many mechanisms could explain the preventative effect of fruit and vegetable consumption. Fiber content may bind to estrogen thereby inhibiting the estrogen enterohepatic reabsorption. Antioxidants in fruits and vegetables also reduce oxidative stress and inflammation by protecting the DNA from damage and by inducing detoxifying enzymes. Vitamin C, found especially in citrus fruits, has been shown to benefit the immune system, while vitamin E and carotenoids have been found to have chemopreventive effects .
Women in Saudi communities eat seafood and fish regularly, especially on holidays. Our study indicates that consuming up to 5 servings of fish and seafood weekly reduces the risk of breast cancer by 78.9–92.8%. The positive effect of fish consumption appears to be limited to certain common types of cancer including breast cancer . Engeset et al. , however, found no evidence of an inverse correlation between overall fish intake and the risk of breast cancer. Fish are a known source of omega 3 fatty acids, or polyunsaturated fatty acids (PUFAs), which can reduce the risk of breast cancer . Their study showed that PUFAs inhibit the epidermal growth factor receptor, which in turn reduces the proliferation of breast cancer.
Our study found that the consumption of coffee and black tea has a negative relationship to the development of breast cancer. In black tea, several antioxidant compounds and chemoprotective components are well known; catechins, particularly gallate epigallocatechin, exerted important antioxidant properties by decreasing the number of reactive oxygen species . Other coffee components such as cafestol and kahweol are known to have antioxidant and anticarcinogenic effects. Kahweol restricts the proliferation of the breast cells and causes apoptosis; it also increases the synthesis of reactive oxygen species to produce cytotoxicity . Another mechanism by which coffee reduces the risk of breast cancer is the inflammation, apoptosis, and other biological processes that reduce inflammatory markers circulating in the bloodstream, as well as insulin resistance which plays a role in developing breast cancer . Yang et al.  explained the anticancerogenic mechanisms of black tea: its antioxidant effect protects the cell and DNA from being damaged by the free radicals. The phenolic compounds in coffee are known to have antioxidant, antimutagenic, and anticarcinogenic effects against several forms of cancer. A follow-up study by Ganmaa et al.  found a weak inverse link between caffeine consumption and the risk of postmenopausal breast cancer. Another article from Saudi Arabia supported our findings that caffeine content in coffee and tea provides effective prevention of breast tumor growth and/or recurrence .
A systematic review and meta-analysis published in 2015 indicated that the increased consumption of saturated fat positively affected breast cancer incidence . Moreover, high consumption of meat has also been shown to increase the risk of developing breast cancer . However, study results did not show a remarkable effect of high fat intake from meat and processed meat and the risk of breast cancer. It is noteworthy to perform further studies regarding this point considering the different types of meat and processed meat consumed locally.
This study is limited by the semiquantitative measurement of food intake, which is a common problem with studies that use food frequency questionnaires, as well as recall bias. This study was also limited by the regional sample collection, relatively small sample size, and recruitment of exclusively postmenopausal women for both case and control groups.