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Diet And The Breast Microbiome

Is the Mediterranean style diet the future in breast cancer prevention? The following study was done in primates, but it makes sense that the results would also be true for humans: that the type of diet eaten influences the breast microbiome. This means the community of microbes that live in the breast. Yes, it's true - studies show that there is a breast microbiome and it varies between those who have breast cancer and those who don't (healthy breasts).

The study looked at macaque monkeys who were fed either a Mediterranean style diet or a Western style diet for 31 months, and then their breast tissue was examined. They found microbial differences in the breast tissue among the 2 groups, including  greater numbers (abundance) of Lactobacillus species in the primates that had been eating the Mediterranean diet.

Lactobacillus species are generally considered beneficial to humans (which is why they are added to many foods and supplements) and studies suggest they may have anti-tumor effects. Some research has found microbial differences between healthy and malignant (cancerous) human  breast tissue  - including lower Lactobacillus numbers or "abundance" in the malignant breast tissue (compared to those with benign breast lesions). Researchers say it suggests that microbial imbalances (dysbiosis) of breast tissue could be a possible driver of breast cancer .

Studies already show that a person's diet influences the gut microbiome. This study shows diet directly influences microbial communities far away from the gut - in the breasts. Unfortunately it is not stated in the study what Lactobacillus species increased in the breast tissue of primates fed a Mediterranean diet. There are many Lactobacillus species, and they are not equal in their effects (as our experiences with Lactobacillus sakei and sinusitis has shown).

Of course more studies are needed, but in the meantime - eat a diet rich in fruits, vegetables, whole grains, legumes (beans), nuts, and seeds. There are many other documented health benefits from a diet rich in those foods (frequently referred to as a Mediterranean diet). The diet is low in processed foods and high in fiber, and rich in "real foods". From Science Daily:

Diet affects the breast microbiome in mammals

Diet influences the composition of microbial populations in the mammary glands of nonhuman primates, researchers report October 2 in the journal Cell Reports. Specifically, a Mediterranean diet increased the abundance of probiotic bacteria previously shown to inhibit tumor growth in animals

"We showed for the first time that breast-specific microbiome populations are significantly affected by diet, and this was in a well-established nonhuman primate model of women's health, increasing the likelihood that these findings will be important for human health," says first author Carol Shively of the Wake Forest School of Medicine. "The breast microbiome is now a target for intervention to protect women from breast cancer."

Diet has been extensively studied as a lifestyle factor that could influence breast cancer development. Breast cancer risk in women is increased by consumption of a high-fat Western diet full of sweets and processed foods but reduced by a healthy Mediterranean diet consisting of vegetables, fish, and olive oil. Intriguingly, a recent study in humans revealed that malignant breast tumors have a lower abundance of Lactobacillus bacteria compared to benign lesions, suggesting that microbial imbalances could contribute to breast cancer.

"However, it was unknown what possible factors could modulate the breast tissue microbiome," says senior study author Katherine Cook of the Wake Forest School of Medicine. "Diet is a strong influencer on the gut microbiome, so we decided to test the hypothesis that diet can impact mammary gland microbiota populations."

To address this question, Shively and Cook used macaque monkeys because the animals mimic human breast biology and have been used to study breast cancer risk. One advantage over human studies is that the food intake of the monkeys can be carefully controlled for a prolonged period of time, increasing the chance of observing profound effects of diet.

The researchers assigned 40 adult female monkeys to receive either a Western or a Mediterranean diet for 31 months. The breast tissue of monkeys that consumed a Mediterranean diet had a 10-fold higher abundance of Lactobacillus, which is commonly used in probiotics and has been shown to decrease tumor growth in animals with breast cancer. The Mediterranean diet also increased levels of bile acid metabolites and bacterial-processed bioactive compounds that may decrease breast cancer risk.

Taken together, these results suggest that diet directly influences microbiome populations outside of the intestinal tract and could impact mammary gland health. But for now, it is not clear what impact these microbes or microbial-modified metabolites have on breast cancer risk.

Excerpts from the actual study by C. A. Shively et al from Cell Reports: Consumption of Mediterranean versus Western Diet Leads to Distinct Mammary Gland Microbiome Populations.

Recent identification of a mammary gland-specific microbiome led to studies investigating bacteria populations in breast cancer. Malignant breast tumors have lower Lactobacillus abundance compared with benign lesions, implicating Lactobacillus as a negative regulator of breast cancer. Diet is a main determinant of gut microbial diversity. Whether diet affects breast microbiome populations is unknown. In a non-human primate model, we found that consumption of a Western or Mediterranean diet modulated mammary gland microbiota and metabolite profiles.

Mediterranean diet consumption led to increased mammary gland Lactobacillus abundance compared with Western diet-fed monkeys. Moreover, mammary glands from Mediterranean diet-fed monkeys had higher levels of bile acid metabolites and increased bacterial-processed bioactive compounds. These data suggest that diet directly influences microbiome populations outside the intestinal tract in distal sites such as the mammary gland. Our study demonstrates that diet affects the mammary gland microbiome, establishing an alternative mechanistic pathway for breast cancer prevention.

Diet has been extensively studied as a modifiable component of lifestyle that could influence breast cancer development. The Mediterranean diet is considered to be one of the healthiest dietary habits (Willett et al., 1995). Mediterranean dietary patterns are characterized by consumption of cereals (preferably as whole grains), legumes, nuts, vegetables and fruits, fish or seafood, white meat and eggs, and moderate to small amounts of poultry and dairy products. The principal source of dietary lipids in the Mediterranean diet is olive oil. It has been suggested that a Mediterranean dietary pattern can protect against diabetes, cardiovascular disease, and cancer (Haegele et al., 1994, Pelucchi et al., 2009).

Reported consumption of a Mediterranean diet pattern was associated with lower breast cancer risk for women with all subtypes of breast cancer, and a Western diet pattern was associated with greater risk (Castelló et al., 2014). Protective effects of Mediterranean diet pattern on breast cancer risk were also observed in a recent prospective cohort study (Buckland et al., 2013) and a randomized, single-blind, controlled field trial in which participants were randomly allocated to a Mediterranean diet supplemented with either extra-virgin olive oil or mixed nuts or a control diet and advised to reduce dietary fat (Toledo et al., 2015). Associations between dietary intake and cancer may not be ascribed to a single nutrient but rather to multiple nutrients and foods and their synergistic effects. Thus, assessing diet as a whole, on the basis of overall dietary patterns, may provide more useful information on the role of diet in breast cancer risk than a single-nutrient approach.

To investigate the potential of diet pattern to modify breast tissue-specific microbiota populations, we obtained mammary gland samples from female Macaca fascicularis monkeys fed a Western diet or a Mediterranean diet for 31 months. This species is a well-established model of women’s health, with considerable use in the study of breast cancer risk (Dewi et al., 2013, Shively et al., 2004, Stute et al.,2006,  Stute et al., 2012, Wood et al., 2006, Wood et al., 2007a, Wood et al., 2007b, Wood et al., 2007c).  ...

Using a non-human primate model, we demonstrated that diet alone may modulate mammary gland microbiota population. Consumption of Mediterranean diet resulted in an approximate 10-fold increase in mammary gland Lactobacillus abundance compared with mammary tissue from Western diet-fed monkeys. Lactobacillus is often thought of as commensal bacteria and is commonly used in probiotic formulations. Oral consumption of Lactobacillus decreased triple-negative 4T1 breast cancer tumor growth in a syngeneic breast cancer model (Aragón et al., 2014, Maroof et al., 2012). This anti-tumor effect is thought to be mediated by immune cell modulation. ... Our study now provides strong evidence that dietary intake alone may modulate the mammary gland microbiome (Figures 2C and 3), especially because subjects were living side by side in the same building, representing a breast cancer prevention model.

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