Flaxseeds Influence Gut Microbiome and May Reduce Breast Cancer Risk

Flaxseeds top a dish that includes bananas.
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  • Researchers found a link between the gut microbiome and expression of miRNAs in breast tissue in mice, one influenced by flaxseed lignans.
  • miRNAs are molecules that regulate the expression of genes, which affects the kinds and amounts of proteins made in cells.
  • Experts caution that while animal studies can help us understand connections like this, the results may not apply directly to humans.

Flaxseeds and other foods rich in lignans may reduce the risk of developing breast cancer, suggest preliminary results from an animal study.

More research is needed, though, including clinical trials in people.

In the study, published Dec. 7 in Microbiology Spectrum, researchers focused on how lignans influenced the relationship between the gut microbiome — bacteria and other microbes living in the gastrointestinal tract — and the generation of microRNAs (miRNAs) in the mammary gland.

miRNAs are noncoding RNAs that regulate the expression of genes in cells, which affects the kinds and amounts of proteins made there.

“If these findings are confirmed, the microbiota becomes a new target to prevent breast cancer through dietary intervention,” study author Elena M. Comelli, PhD, associate professor in the Department of Nutritional Sciences at the University of Toronto in Canada, said in a news release.

Flaxseed’s effects on the microbiome

In the study, researchers examined the effect of flaxseed lignans on the gut microbiome of young female mice. In particular, they looked at the amounts and types of microbes in the cecum, the first part of the colon. 

Flaxseeds are the richest dietary source of lignan precursors, but these compounds are also found in other seeds, whole grains, legumes, fruit and vegetables.

When plant lignans are ingested, they can be converted by intestinal bacteria to other compounds that are absorbed into the bloodstream. 

Some previous research has found that postmenopausal women who consume higher amounts of lignans in their diet have a lower risk of breast cancer. Another 2010 study found that dietary intake of lignan was associated with a lower risk of dying from breast cancer.

Jo L. Freudenheim, PhD, professor in the Department of Epidemiology and Environmental Health in the University at Buffalo’s School of Public Health and Health Professions, the lead author of 2010 study, said the findings of the new research might provide a potential mechanism for the results seen in her study. 

Gut microbiome and gene expression

In the new study, researchers found a relationship between the cecal microbiome and mammary gland miRNA expression, which was altered by a diet containing flaxseed lignan components.

In particular, mice fed lignan components generated specific miRNA responses in the mammary gland, including the production of miRNAs related to the regulation of genes involved in breast cancer.

“[This study] shows changes in the expression of miRNAs in the breast with changes in the gut microbiome, with possible changes in metabolic processes that could be important in breast cancer,” Fruedenheim told Healthline.

“This provides some evidence for another potential mechanism linking the gut microbiome with breast cancer,” she said.

However, she said there are a large number of steps that must occur in the body between the changes in miRNAs and the development of cancer, both in mice and in people.

In addition, “it is not clear to what extent the microbiota profiles that [the researchers] are studying in a laboratory setting are relevant to humans living in a more complex environment,” she said.

Gut microbiome and cancer risk

Freudenheim pointed out that several possible mechanisms for how the gut microbiome might affect breast cancer risk have been explored. For example, the gut microbiome may affect the levels of estrogen circulating in the bloodstream. 

Or bacterial products may pass from the intestines into the blood and impact other organs, including breast tissue. Additionally, bacteria in the gut may lead to inflammation throughout the body.

However, it’s not just gut microbes that can affect breast tissue.

“[My colleagues and I] did a study looking at periodontal disease, a disease with an altered oral microbiome, and showed that it was associated with increased breast cancer risk,” said Freudenheim.

She cautions that while animal studies, like the new one and others, can provide insight into biological processes, there can be significant differences between experimental animals and humans. 

So the findings of the new study may not directly apply to people. Additional research, including randomized clinical trials in people, are needed to show whether supplementing the diet with lignans can protect against breast cancer.

Freudenheim points out that a person’s microbiome is constantly interacting with their body, so it can have a big impact on health.

As a result, studies like this have “enormous potential to impact our understanding of the processes of health and disease, and potential to provide insight for health and disease prevention,” she said.

Takeaway

In a new study, researchers fed flaxseed lignans to female mice, and found that this changed the composition of the gut microbiome and the miRNAs produced in breast tissue.

miRNAs are a non-coding type of RNA that regulate the expression of genes, which affects which proteins are made by cells.

Mice fed flaxseed lignans produced miRNAs in breast tissue that are involved in the development of breast cancer. This suggests dietary changes may be able to reduce breast cancer risk. However, clinical trials in people are needed.

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