Yet Another Microbiome

Yet Another Microbiome

As with most of my readers, I am well aware of the gut microbiome, and of the recent discovery of the brain microbiome (for more info, see this blog on the subject). Still, it came as a surprise to me to find a study which concerns the breast microbiome, and how it relates to cancer. And, before the men reading this change the channel, remember that pretty much everything that can cause breast cancer can also contribute to the development of prostate cancer (xenoestrogens being one example). As well, if the breast has a microbiome, I am pretty sure it will soon be discovered that the prostate does as well.

By definition, “a microbiome is the collection of microorganisms that live in a particular environment in the body”.  The fact that the breast has a distinct microbiome was discovered a few years ago, but first brought to the fore in 2018, by researchers from the Wake Forest School of Medicine. That year they released a study showing that, like the gut microbiome, the microbiota in the breast responds to diet and dietary changes.

Now, diet has long been studied to determine its influence on the development of breast cancer. And, it has been established that a high-fat Western diet, including lots of sugar and processed foods, dramatically increases the risk of developing breast cancer. Whereas, following a diet such as the Mediterranean diet, including fish, olive oil, and plenty of vegetables, will clearly reduce that risk.

The scientists from Wake Forest were well aware of this information, when new information became available revealing that malignant breast tumors contain far less Lactobacillus bacteria than benign lesions. This implied that an imbalance in the microbiome could be a factor in breast cancer.  According to senior study author Katherine Cook,“Diet is a strong influencer on the gut microbiome, so we decided to test the hypothesis that diet can impact mammary gland microbiota populations”.


For this study, the researchers used macaque monkeys, as that species mimics human breast biology, and have in the past been used in breast cancer risk studies. As well, in primate studies the diet can be absolutely controlled for long periods of time, as opposed to human studies, where researchers must rely on unreliable humans to fully follow the dictates of the recommended dietary intake, without variance.

After two groups of monkeys spent 31 months on either a Mediterranean diet, or a standard Western diet, the results were clear. Those monkeys on the Mediterranean diet had ten times more Lactobacillus in their breast microbiome than those receiving the Western diet. (Note: previous studies have shown Lactobacillus species to decrease tumor growth in animal models of breast cancer.)

The Mediterranean diet also “increased levels of bile acid metabolites and bacterial-processed bioactive compounds”, which further aided in decreasing breast cancer risk.  Concluding that diet has a direct effect on microbiome populations outside of the gut, and may have a direct impact on the health of the mammary glands, the researchers planned to carry on with related research.

Study author Katherine L. Cook, Ph.D, stated that, “Our future studies are designed to validate the use of probiotics, fish oil, or antibiotics during neoadjuvant therapy to improve therapeutic outcomes”.   (As well, they will be exploring the value of bile acids on breast cancer tumor growth.”)

Study: Consumption of Mediterranean versus Western Diet Leads to Distinct Mammary Gland Microbiome Populations

Part Two

So, in May 2021, our intrepid crew from Wake Forest School of Medicine returned with some of that aforementioned follow up research, which was published by the American Association for Cancer Research.  In order to further their understanding of the relationship between diet, the microbiome, and cancer, this time these researchers studied both animal models, and humans with breast cancer.


In this study, senior author Cook, opens with the statement that, “Obesity, typically associated with a high-fat diet consumption, is a well-known risk factor in postmenopausal breast cancer”.  Thus, in the first part of the study, mice (engineered to be prone to breast cancer) were fed either a low-fat or a high-fat diet.

As was expected, the mice on a high-fat diet had more tumors, and larger, faster developing tumors, than those rats on the low-fat diet. But, now comes the part that was not so expected.  In order to examine the role of the microbiome in this tumor development, the mice received fecal transplants. Those mice on the high-fat diet received the microbiome (fecal) transplant from the low-fat diet mice, and vice versa.

Eventually it was revealed that the mice consuming the low-fat diet, who received a high-fat diet microbiome, developed just as many breast tumors as those mice consuming the high-fat diet.

“Simply replacing the low-fat diet gut microbiome to the microbiome of high-fat diet consuming animals was enough to increase breast cancer risk in our models,” Cook said. “These results highlight the link between the microbiome and breast health.”


Now onto the human trials in this study. In a proper double-blind placebo-controlled clinical trial, patients with breast cancer were given a fish oil supplement, or placebo, for two to four weeks before lumpectomy or mastectomy.

Why fish oil?  Well, we know fish is an important part of the Mediterranean diet, and we have already established that the Mediterranean diet improves the microbiome of the gut, and, as we saw above, that of the breast as well. Results from this part of the study showed that supplementation with fish oil significantly altered the breast microbiome in both non-cancerous and malignant breast tissue. For those subjects who received the fish oil supplements for the longer period (four weeks), there was a large increase in the abundance of Lactobacillus in the breast tissue.

This study provides additional evidence that diet plays a critical role in shaping the gut and breast microbiomes,” Cook said. “Ultimately, our study highlights that potential dietary interventions might reduce breast cancer risk.”

The research team from Wake Forest are now conducting studies to determine if probiotic supplements can affect the microbiome in mammary glands and breast tumors.  (Study: Diet alters entero-mammary signaling to regulate the breast microbiome and tumorigenesis)


In these days of Keto and Paleo diets, I would like to point out that the high-fat/low-fat diets the mice were put on were based on the “Western” diet (also known as “SAD”: Standard American Diet).

Thus, in this case, the fat is mostly from omega 6 sources (which are inflammatory in nature), and “bad” fats, such as those found in deep fried and processed foods (over-heated vegetable oils, trans fats, and hydrogenated oils).

My point being that a high-fat diet is not in and of itself necessarily worse than a low-fat diet, unless it is based on denatured and damaged fats, and a poor ratio of omega 6 fatty acids, to the omega 3 (fish, flax) and omega 9 (olive, avocado) fatty acids.

Finally, as usual, I will mention a couple of NutriStart products that are germane to these studies. As support for the microbiome I recommend LactoSpore, which will encourage the colonization of Lactobacillus species in the body. And as a fish oil supplement I suggest NutriKrill, which is five times more effective than conventional fish oil, and thus has a therapeutic dose of only three small (500 mg) caps per day.

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