Gone Fishing: Fish Oil Supplements Reduce Impacts of Breast Cancer in Obese Mice

By Sarah Kirsh

22 July 2021

Fish Oil Capsules

Have you ever wondered what your fish oil supplements are doing for you? Luckily, researchers in the Department of Human Health and Nutritional Sciences are working to answer this question.

Dr. Jennifer Monk and Dr. David Ma, both professors of nutrition, recently discovered that omega-3 fatty acids found in fish oil can reduce the number and size of breast tumours in obese mice.

Monk studies the role of fatty acids in chronic diseases and has a particular interest in obesity, while Ma’s research focuses on the role of omega-3 fatty acids in breast cancer.

“I had collaborated with David in the past on obesity studies and his breast cancer work with omega-3 fatty acids, so it was a natural progression to look at the influence of omega-3 fatty acids in an obese breast cancer model,” explains Monk. “It also makes particular sense when you consider that we are seeing increasing rates of obesity both globally and in Canada, and obesity has been shown to increase breast cancer severity.”

Monk and Ma used a genetic mouse model with a form of breast cancer that overexpresses the human epidermal growth factor receptor 2 (HER2). This is the same type of cancer found in 25-30% of invasive breast cancer cases in humans. It is also associated with a poor prognosis and aggressive tumour growth.

To compare the impact of fish oil on breast cancer in obese mice, the researchers divided the mice into three groups based on diet. The groups included a high-fat diet that serves as an obese control, a high-fat diet with fish oil supplementation, and a low-fat diet that served as a non-obese control.

“The level of fish oil supplementation we tested was very high, in terms of what most Canadians typically consume in their diet,” says Monk, noting that the level used was on par with that of the Greenland Inuit diet, which is traditionally very high in omega-3 fatty acids. “However, these levels can also be easily achieved through commonly consumed supplements.”

Over the course of the study, the researchers measured tumour development and size in the different groups of mice. After 20 weeks, all tumours were surgically removed for analysis.

“The major outcomes we saw were that fish oil supplemented obese mice developed fewer tumours and had lower tumour weight and volume compared to obese control mice,” says Monk.

This was an exciting finding for the researchers.

“You might see subclinical changes with a dietary intervention, but to observe a functional outcome with reductions in tumour number and size is the most meaningful outcome to see,” says Monk.

The team also examined tissue within the tumours to see if they could determine how the omega-3 fatty acids were causing a reduction in tumour number and size.

“The possible mechanisms seem to be promoting controlled cell death of tumour cells, and reducing inflammation within the tumours,” says Monk.  Controlled cell death is a normal function that gets disrupted in cancerous cells, allowing the cells to live and divide uncontrollably.

So, what do the researchers have in store for the future, given these promising findings?

The research team, which also includes HHNS colleague Dr. Lindsay Robinson, would like to see if similar beneficial impacts on tumours occur with a lower level of fish oil supplementation that is more achievable with the typical Canadian diet. They are also interested in testing mouse models with other types of breast cancer to determine if their results are representative of a broader population of breast cancer patients.

“Breast cancer is the second leading cause of death for women in North America,” says Ma. “Using specialized mouse models offers a practical and valuable approach for studying breast cancer and obesity, and for testing potential prevention strategies.”


This study was funded by the Natural Sciences and Engineering Research Council and the Canadian Institutes of Health Research.


Read the full study in The Journal of Nutritional Biochemistry.

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