Soy, cabbage reduce symptoms after breast cancer treatment

Eating soy-based foods and vegetables such as cauliflower, cabbage and bok choy could help the symptoms of menopause experienced by some breast cancer survivors who take hormone treatment, according to a new study.

Successful cancer therapy is often followed up with drugs, such as Tamoxifen, that block the female hormone oestrogen. Around 70% of tumours are sensitive to oestrogen, which makes them grow more aggressively, and Tamoxifen can nearly halve the risk of the cancer returning.

But the treatment has side effects. Shutting down oestrogen can trigger disabling symptoms of menopause, including hot flushes and night sweats. Enter the vegetables.

Cruciferous vegetables of the cabbage family, so named for the cross-shaped petals of their flowers, as well as soy-containing foods such as tofu, edamame and soy milk, can mimic the effects of oestrogen.

They contain phytochemicals – biologically active plant compounds – including isoflavones in soy that bind to oestrogen receptors, and glucosinolates in the cabbage group that alter oestrogen metabolism.

The researchers, led by oncologist Judy Huei yu Wang at the Lombardi Comprehensive Cancer Centre, Georgetown University, US, wanted to see if these foodstuffs protect against menopause symptoms, as well as the fatigue, memory loss and joint problems often seen with hormone treatment.

To find out they surveyed 365 Chinese-American and Non-Hispanic White breast cancer survivors in the Los Angeles and San Francisco Bay areas of California.

They found women who ate more cruciferous vegies reported, across the board, fewer menopause symptoms. Higher soy intake was also linked to a decrease in menopause symptoms, and less fatigue, but the findings were only significant in the Non-Hispanic White group.

A beneficial effect of soy could be harder to detect in Chinese-Americans, the researchers suggest, because these women typically get fewer menopause symptoms and eat more soy-based foods.

The stakes, however, go beyond mere symptom control, distressing as they may be.

“These symptoms can adversely impact survivors’ quality of life and can lead them to stopping ongoing treatments,” said Sarah Nomura, the study’s first author, a nutritionist at Georgetown Lombardi.

But for women wondering whether to alter their diet, there is a complicated back story.

It is unclear whether eating oestrogen-boosting foods could work against Tamoxifen, increasing the risk of cancer recurrence for women with oestrogen-sensitive tumours.

Adding confusion, isoflavone is also known to decrease oestrogen production, which might actually be a benefit in some breast cancers. A study of more than 6000 women with breast cancer, published in June, linked higher isoflavone intake with a 21% reduction in mortality from all causes.

The researchers’ conclusions in the current study are, accordingly, circumspect.

Leena Hilakivi-Clarke, a professor of Oncology at Georgetown University and a co-author, says breast cancer patients shouldn’t suddenly start eating soy if they haven’t before.

The authors also write that additional research is needed with “prospective data collection in a larger, diverse study population.”

The paper appears in the journal Breast Cancer Research and Treatment.