The Mediterranean diet is rich in fish, nuts, fruits, and vegetables, as well as olive oil.
So concluded researchers from the Wake Forest School of Medicine in Winston-Salem, NC, after having compared the effects of Western and Mediterranean diets on the microbes and biologically active compounds in the mammary glands of monkeys.
In a paper on the work, which will soon appear in the journal Cell Reports, they suggest that their findings could open a new avenue for breast cancer prevention and treatment.
For the next most common cancer, that of the lung and bronchus, there were 58 new cases per 100,000.
The breast microbiome
Recent studies have found that the human mammary gland, similarly to the gut, has its own specific microbiome, or unique population of microbes.
Further investigation also found that breast cancer tumors contain lower levels of Lactobacillus bacteria species compared with non-cancerous growths, suggesting that they could be "a negative regulator of breast cancer."
Women's breast cancer risk is known to vary with diet. A healthful diet, such as the Mediterranean one — which is rich in fruits, nuts, vegetables, legumes, fish, and olive oil — reduces the risk, whereas a typical Western diet high in fat, processed foods, and candy increases it.
However, while there is evidence that diet has a major impact on the diversity of gut microbes, it has not been clear whether this might also be true of the breast microbiome.
This is why, says senior study author Dr. Katherine L. Cook, an assistant professor in the Wake Forest School of Medicine, the scientists "decided to test the hypothesis that diet can impact mammary gland microbiota populations."
'Implications for mammary gland health'
The scientists decided to carry out the study in macaque monkeys because they are a good model for breast cancer, and it is possible to closely control their diet for long periods — something that is very difficult in human studies.
For 31 months, 40 female adult monkeys ate either a Mediterranean or Western diet. After this time, the monkeys that ate the Mediterranean diet had 10 times the level of Lactobacillus in their breast tissue as that measured in those that ate the Western diet.
The Mediterranean diet-fed monkeys also had higher levels of compounds produced from bile and bacterial activity that are consistent with a lower risk of breast cancer.
The investigators say that these findings reveal the direct influence of diet on a microbiome that is not in the gut, with implications for "mammary gland health." However, further work is needed to determine the effect of bacteria and their metabolic byproducts on breast cancer risk.
Dr. Cook and her team plan to continue the research, starting with an investigation of how raising levels of Lactobacillus might impact breast tissue.
After that, they want to test whether or not adding supplements — such as probiotics and fish oil — to the diet alters the microbiome in breast tissue and tumors.
"Our future studies are designed to validate the use of probiotics, fish oil, or antibiotics during neoadjuvant therapy to improve therapeutic outcomes."
Dr. Katherine L. Cook