Better Together: Diet and Exercise Impact Breast Cancer Development

These days, it feels like we hear about a new diet or nutrition fad every week. From the viral carnivore diet to the era of GLP-1 inhibitors, society is more focused than ever on what we should or shouldn’t be eating. But while diet trends come and go, researchers in the Department of Human Health Sciences are taking a longer view, exploring how diet influences chronic disease and long-term health.

Dr. David Ma, a professor of nutrition, has a particular interest in how healthy dietary fats impact cancer prevention and health. His research group has done extensive work investigating the protective role of omega-3 fatty acids against breast cancer. 

Recently, he and his team decided to add another variable to their work.

“As scientists, we’re often trained to be reductionists — to think in terms of one pathway, one molecule, one mechanism,” Ma says. “But in reality, there is no magic bullet. Except in the case of single-gene mutation diseases, almost all health conditions are multi-factorial.”

For that reason, Ma’s team, including research associate Lyn Oakes and co-investigator Dr. Lindsay Robinson, decided to combine two major lifestyle factors — diet and exercise — and see what their combined effect was on breast cancer prevention.

Studies have long shown that groups with diets rich in omega-3 fatty acids (such as Asian populations) have a lower risk of developing breast cancer, while those with diets enriched in saturated and omega-6 fatty acids (such as Western populations) have a higher risk.

At the same time, exercise has also been found to reduce breast cancer risk and can even provide therapeutic benefits during and after treatment. So does this mean that combining omega-3 fats and exercise could offer a more powerful one-two punch against breast cancer? This is what the team set out to test, using a genetic mouse model that mimics a common and aggressive form of human breast cancer known as Her-2.

Starting in utero and continuing after birth, mice were fed a diet rich in either omega-3 fatty acids (from fish oil) or omega-6 (from safflower oil) and were either exercised vigorously or kept sedentary. Mammary tumours were then counted and measured, starting at 10 weeks of age (roughly the equivalent of a woman in her twenties) and continuing until 20 weeks of age.

As expected, the omega-6 group had consistently more and larger tumours than the omega-3-fed mice throughout the trial. More surprisingly, the exercised omega-6 mice had the most and largest tumours, even compared to their sedentary counterparts.

But the most intriguing result came not from the “destination” of tumour outcomes, as Ma puts it, but rather from the “journey” of tumour progression. Although all the mice ultimately developed tumours, the exercised omega-3 mice remained tumour-free the longest, developing their first tumours 9% later than their sedentary counterparts, 16% later than the sedentary omega-6 mice, and 26% later than the exercised omega-6 mice.

Collectively, these findings revealed that, in conjunction with a diet of omega-3 fatty acids, exercise tended to increase the time spent disease-free, rather than change the outcome of cancer itself. Furthermore, exercise combined with omega-6 fatty acids resulted in more, larger, and earlier tumours, possibly through the stimulation of inflammatory pathways as seen in previous studies.

This research ties into a burgeoning area of interest called "healthspan" research, which focuses on extending the number of years lived in good health, rather than just simple longevity.

“Living a healthy life is a lot like investing,” says Ma. “Just like saving a bit of money each month leads to long-term growth, things like eating well and exercising can help us stay healthy for longer. That doesn’t mean we can’t be flexible — you can still have a slice of birthday cake or skip the occasional trip to the gym. But having the knowledge and tools to live healthier is crucial. Simple solutions can be just as effective as complex ones.”

This study was funded by the Cancer Research Society.

Read the full study in the journal Nutrients.

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