Breast cancer and plant-based diets: Unhealthy foods linked to 20% higher risk

• Body-mass index and diet have both been linked to increased cancer risk, though the exact nature of the mechanism behind this is not well understood, and is assumed to be multifactorial.
• New research has shown a diet rich in fruit, vegetables, whole grains, and nuts may reduce the risk of developing breast cancer in postmenopausal women.
• The same study found that breast cancer risk may increase in postmenopausal women who eat an “unhealthy” diet rich in refined grains, fruit juices, potatoes, and processed products of plant origin.

The food we eat, what we drink, and our lifestyle influence our cancer risk. According to Cancer Research U.K., certain foods are directly linked to the risk of developing cancer but overall diet is more important, helping maintain a healthy weight.

However, there is strong evidence that eating more whole grains and fiber reduces the risks of cancer, and that processed meat is “carcinogenic to humans”.

Vegan and vegetarian diets may, in particular, have health benefits as they have been associated with better health outcomes for type 2 diabetes and heart disease.

New research at Paris-Saclay University has studied the association between a plant-based diet and breast cancer risk among postmenopausal women.

The work was presented at the American Society for Nutrition, Nutrition 2022 live online meeting held from June 14-16. Led by doctoral candidate Sanam Sha, the study investigated how the quality of plant foods—healthy and unhealthy—may be linked with different outcomes.

Not all plant-based diets are equal

Researchers collected data from over 65 000 women from the Etude Epidémiologique auprès de femmes de la Mutuelle Générale de l’Education Nationale study (E3N) for over two decades.

The researchers identified and classified the cases of breast cancer using receptor and histological subtypes. The patients self-reported their diets and the researchers scored them as healthful and unhealthful plant-based diets.

The researchers recorded nearly 4,000 cases of breast cancer during the study. The risk of breast cancer among the participants was reduced the more they adhered to a healthy plant-based diet, the results showed.

The researchers found that the women who regularly ate a healthy plant-based diet—even if it included animal-based foods—were 14% less likely to develop breast cancer. The results were applicable to all breast cancer subtypes.

This was compared to women who ate a more unhealthy plant-based diet, which included foods such as fruit juices, potatoes, and dessert. This group had a 20% higher risk of breast cancer, in comparison.

Plant-based vs. vegetarian

“Plant-based diets are often used interchangeably with vegetarian or vegan diets,” said Sha.

“However, a healthy plant-based diet comprises higher intakes of fruit, vegetables, whole grains, nuts, legumes, tea, and coffee. In contrast, the unhealthy plant-based diet comprises higher intakes of primarily processed/refined products of plant origin such as refined grains, fruit juices, sweets/desserts, and potatoes. In both instances, the diet still includes some animal-based foods,” she detailed to Medical News Today.

Plant-based with occasional meat

Speaking to MNT about the study findings, Sha explained:

“Eating more healthy plant foods while not cutting out meat/animal foods entirely has health benefits and could prevent breast cancer”.

“[…] our results suggest that not all plant-based diets are equally healthy, which may be surprising as diets excluding meat generally have a ‘positive’ health image.”
— Sanam Sha, lead author

When asked if these findings may also be relevant to pre-menopausal breast cancer, Sha said that due to the differences in the development of breast cancer, they could not conclude that the same results might apply to young women.

She said the same applied to male breast cancer.

“A gender difference in cancer susceptibility has been found. Hence, we need more studies to assess the link between plant-based diets and cancer risk in men,” she added.

More research needed

This study emphasizes the importance of not only diet but diet quality on health and possibly breast cancer risk.

According to Sha, the research “[..] highlights 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 in postmenopausal women.”

Calling it “a novel area of research”, Sha said their findings suggest that eating a diet based on healthy plant foods could benefit postmenopausal women with a poor diet.

However, the mechanisms behind any link are not yet known. When speaking about the next steps for the work, Sha elaborated that they needed more studies on diverse populations in different countries to better assess this risk and possible underlying mechanisms.

“The remaining key questions include assessing the underlying mechanisms of the associations observed between the healthy and unhealthy plant-based diets and breast cancer risk, such as the mediating role of the circulating levels of some metabolites or gut microbiome studies,” she added.

“Moreover, previous studies have suggested that a healthy plant-based diet may lower the risk of other diseases such as diabetes and hypertension. Therefore, it is probable that it is never too late to embark on a healthy plant-based diet.”
— Sanam Sha

The study did not adjust its findings for any other factors, which means that it can’t be ruled out that other external factors, such as socioeconomic status, have had an effect on the results.

Fiona Osgun, senior health information manager at Cancer Research U.K., who was not involved in the study told MNT that although“[a]vailable research does not support a link between types of diet and breast cancer[…] a healthy balanced diet lowers your risk of getting cancer overall, mainly by helping to keep a healthy weight.

“You don’t have to be vegetarian or vegan to be healthy, just try to eat more vegetables, fruit, wholegrain foods, and healthy sources of protein like beans or fresh chicken,” she added.

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