After tracking more than 65,000 women for two decades, investigators found those who consumed a healthy, primarily plant-based diet saw their risk for developing any type of breast cancer drop by an average of 14%.
But the accent is on “healthy.” Breast cancer risk fell only among women whose diets included a significant amount of whole grains, fruit, vegetables, nuts, legumes, vegetable oils and tea or coffee — even if red meat and poultry occasionally figured into the equation.
By contrast, no protective benefit was seen among older women whose primarily plant-based diet was deemed relatively unhealthy, due to a heavy reliance on sugary fruit juices, refined grains, potatoes, sugar-sweetened beverages and/or desserts. Such women actually saw their breast cancer risk rise by about 20%.
Study lead author Sanam Shah said the findings “highlight that increasing the consumption of healthy plant foods, and decreasing the consumption of less healthy plant foods, might help prevent all types of breast cancer.”
Given that in general “diets excluding meat generally have a ‘positive’ health image,” some people might find that conclusion surprising, said Shah, a PhD student in epidemiology at Paris-Saclay University in France.
But Shah and her colleagues did not focus on women who cut out meat entirely. None of the women were vegetarian or vegan.
Instead, the investigators honed in on women whose diets included some meat and poultry while still being primarily plant-based.
They then delved into whether healthier plant foods had a different impact on breast cancer risk compared to less healthy options, an angle typically overlooked in prior investigations.
For the study, the French female participants (average age 53) completed nutritional questionnaires in 1993 and again in 2005.
The women were classified as following either a mostly animal-based diet or a diet that’s mostly plant-based.
Over an average tracking period of about 21 years, nearly 4,000 of the women developed breast cancer.
The study team found that those who tended to eat the healthiest plant-based foods faced a notably lower breast cancer risk; those who consumed the least healthy plant-based diets saw their risk rise considerably.
As to why, Shah theorized that the high fiber content of healthier plant-based diets “may lower cancer risk via anti-inflammatory and antioxidant effects.”
But she also stressed that more research will be needed, as “the causal mechanisms of the link between healthy plant-based diets and breast cancer risk have yet to be entirely determined.”
Shah also cautioned that it remains unclear whether the findings might apply to younger women. That’s because “differences exist between premenopausal and postmenopausal breast cancers in regards to the development of breast cancer.”
The study results were presented by Shah online on Tuesday at the annual meeting of the American Society for Nutrition. Findings should be considered preliminary until published in a peer-reviewed medical journal.
Lona Sandon, a nutrition specialist in Dallas, agreed that more research will be needed.
Still, adopting a healthy plant-based diet is almost always a win-win, particularly for those who start young, said Sandon, program director of clinical nutrition in the School of Health Professions at University of Texas Southwestern Medical Center. She was not part of the study.
“What distinguishes the difference between a healthy plant-based food and an unhealthy plant-based food is largely the processing or preparation method,” Sandon noted. “In general, the more processing, the more diminished quality due to changes in nutrients or added ingredients.”
With that distinction in mind, there “does not appear to be a downside to choosing minimally processed plant-based foods for anyone when it comes to cancer risk,” she added.
“However, we need to be realistic in expectations,” Sandon cautioned. “If you wait until you are 55, damaged or cancer cells may already have started to progress. So your benefit of risk-lowering is likely to be much less, compared to if you had been eating a healthy plant-based diet since your 20s.”
There’s more on plant-based diets and cancer at the Cleveland Clinic.
SOURCES: Sanam Shah, MBBS, FCPS, MPH, PhD student, epidemiology, Center for Research in Epidemiology and Population Health, Paris-Saclay University, France; Lona Sandon, PhD, RDN, LD, program director and associate professor, clinical nutrition department, School of Health Professions, University of Texas Southwestern Medical Center, Dallas; American Society for Nutrition virtual meeting, June 14-16, 2022