Research shows that what we eat can influence our cancer risk, but it’s not always clear which foods or dietary patterns are best for cancer prevention. Results from a new study suggest that the quality or overall healthiness of a person’s diet may be key.

The study, based on data from over 65,000 postmenopausal women who were tracked for more than two decades, found that a healthy plant-based diet was linked with a 14% lower risk of breast cancer while an unhealthy plant-based diet was linked with a 20% higher risk of breast cancer. The findings were consistent across all breast cancer subtypes.

“These findings highlight that increasing the consumption of healthy plant foods and decreasing the consumption of less healthy plant foods and animal foods might help prevent all types of breast cancer,” said Sanam Shah, a doctoral candidate in the Center for Research in Epidemiology and Population Health at Paris-Saclay University, Inserm, Gustave Roussy, France, the study’s lead author. Shah will present the findings online at Nutrition 2022 live online, the flagship annual meeting of the American Society for Nutrition held June 14-16.

Previous studies have examined cancer risks associated with various dietary patterns such as the Western diet, the Mediterranean diet and vegetarian diets. Although some studies suggest diets with less or no meat consumption offer health benefits, results have been somewhat mixed.

For the new study, researchers focused on differentiating between healthy plant-based foods — such as whole grains, fruit, vegetables, nuts, legumes, vegetable oils and tea or coffee — and plant-based foods the study categorised as less healthy including fruit juices, refined grains, potatoes, sugar-sweetened beverages and desserts.

“What is different about our study is that we could disentangle the effects of the quality of plant foods, which has not been the focus of previous studies on other dietary patterns,” said Shah. “By scoring healthy, unhealthy and animal-based foods, we comprehensively analysed food intake by considering the ‘healthiness’ of food groups.”

The researchers analysed data from 65,574 postmenopausal women living in France who filled out dietary intake questionnaires in 1993 and 2005 and were followed for an average of 21 years. Over the course of the study, 3,968 study participants were diagnosed with breast cancer. Comparing breast cancer rates among women with different dietary quality revealed significant differences in cancer risk among those with healthy and unhealthy diets.

The researchers used 18 food groups to categorise the degree to which participants adhered to a plant-based versus animal-based diet and ate healthy versus less healthy foods. Shah noted that a plant-based diet does not equate to a vegan or vegetarian diet, but rather describes a general emphasis on plant-based foods over animal-based foods.

While the findings suggest that choosing healthy plant-based foods is likely helpful for cancer prevention, Shah noted that more research is needed to assess the connections between diet and cancer risk in diverse populations, in particular, to determine causality.

Shah will present this research on-demand starting at noon on  June 14, during the Nutrition 2022 live online diet and cancer session.

Please note that abstracts presented at Nutrition 2022 live online were evaluated and selected by a committee of experts but have not generally undergone the same peer-review process required for publication in a scientific journal. As such, the findings presented should be considered preliminary until a peer-reviewed publication is available.