When it comes to breast cancer, what you eat matters.
Studies have shown that diets with a lot of saturated fat, processed meats, and red meat are linked to a higher risk of breast cancer. But those that include plenty of vegetables, fruits, legumes, and whole grains help protect against the disease.
A lesser-known legume may also work against breast cancer. Pigeon peas, which are native to tropical countries like India, Senegal, and Nigeria, have a micronutrient called cajanol that helps kill cancer cells in lab tests.
Breast Cancer and Estrogens
Pigeon peas are one of a number of foods with plant-based estrogens, also known as phytoestrogens, that might be especially good for you. Things like tofu, flaxseeds, edamame, miso, and even certain brands of breakfast cereals have a type of phytoestrogen called isoflavones.
Estrogen and other hormones can promote the growth of breast cancer cells. So it might seem risky for people who have breast cancer or who are at high risk of the disease to add phytoestrogens to their diets.
The concern was stoked by research showing that rodents fed diets high in soy had more of a risk of breast cancer. But those findings don’t seem to apply to humans. For one thing, the animals got doses of isoflavones that were much higher than what humans normally get. The rodents’ bodies also handled the soy differently than humans do, which affected their response to the diets.
“Estrogens are found in many foods ... but it doesn’t have that ‘feeding the cancer’ effect that most people fear,” says JoAnna Hazard, MS, RD, director of nutrition at Cancer Treatment Centers of America and a specialist in oncology nutrition.
In fact, research now shows that the opposite might be true: Phytoestrogens might offer some protection against breast cancer.
“Phytoestrogens resemble estrogen in biologic terms but are not human estrogen ... and do not act the same way as human estrogens in our bodies,” explains Stephanie Hopkins, a clinical dietitian at University Hospitals Seidman Cancer Center in Cleveland. “Phytoestrogens actually have antioxidant and anti-inflammatory effects, so there can be a benefit to consuming these plant foods. We need to step away from the fear about phytoestrogens.”
A 2020 study found that plant estrogens like those in soy are powerful antioxidants, which can protect against cell damage. They may limit cell growth in certain tumors and help prevent the gene changes that can lead to cancer.
Also, phytoestrogens might make cancer cells more sensitive to cancer treatments and may protect healthy (noncancerous) cells from the effects of radiation and chemotherapy.
The Benefit of Pigeon Peas
When it comes to pigeon peas, studies have shown that cajanol may offer breast cancer benefits.
“A compound found in pigeon peas has been shown to cause [cancer] cell death,” Hazard explains.
Cajanin stilbene acid, another compound in pigeon peas that’s similar in structure to estrogen, helps kill certain types of breast cancer cells. These benefits are found in both green (immature) and brown (mature) pigeon peas, Hopkins says.
Pigeon peas have only 0.56 milligrams per 100 grams (mg/100g) of isoflavones, far less than other plant-based proteins. Soy-based burgers have about 6.4 mg/100g. Edamame has 48.9 mg/100g, and textured soy flour has 172.6 mg/100g.
Adding Phytoestrogens to Your Diet
The findings aren’t an invitation to eat pigeon peas or other foods with phytoestrogens with wild abandon. Instead, Hopkins suggests moderation for everyone, aiming for two to three servings of phytoestrogens per day. One serving is a cup of soy milk, a half-cup of pigeon peas or edamame, 4 ounces of tofu or tempeh, or 3 tablespoons of flaxseeds.
When it comes to adding phytoestrogens to your diet, Hazard advises choosing minimally processed foods, such as pigeon peas and other legumes, over things like soy burgers.
“There are so many different ‘cancer-fighting’ diets on the market, and the one thing they all have in common is that they are plant-forward,” Hazard says.