Breast cancer treatment: Can Brussels sprouts, soy reduce side effects?

Women who have survived breast cancer might want to pile their plates up with Brussels sprouts this Christmas; a new study has shown that eating these and other cruciferous vegetables, as well as soy foods, could help to reduce some of the long-term side effects of cancer treatment.

Lead study author Sarah Oppeneer Nomura, Ph.D. — of the Lombardi Comprehensive Cancer Center at Georgetown University in Washington, D.C. — and her colleagues recently reported their findings in the journal Breast Cancer Research and Treatment.

Breast cancer is the most common cancer among women in the United States, after skin cancer. This year, it is estimated that 252,710 new cases of breast cancer will be diagnosed in the U.S.

Despite its prevalence, however, more women than ever are now surviving breast cancer. Almost 90 percent of women diagnosed with the disease survive for at least 5 years, and death rates from the disease fell by around 1.8 percent annually between 2005 and 2014.

The reduction in breast cancer death rates is largely down to improvements in treatment strategies, including radiotherapy and chemotherapy. But such treatments are not without side effects.

While most of the side effects of breast cancer treatments diminish once breast cancer treatment ceases, there are some that can persist for months, or even years. These include fatigue and early menopause.

"These symptoms can adversely impact survivors' quality of life and can lead them to stopping ongoing treatments," says Nomura.

Previous research has suggested that soy and cruciferous vegetables may hold some benefits for cancer patients. Nomura and colleagues set out to determine whether this is the case for people who have received treatment for breast cancer.

"Understanding the role of lifestyle factors is important because diet can serve as a modifiable target for possibly reducing symptoms among breast cancer survivors," Nomura explains.

Menopausal symptoms and fatigue reduced

The study included 173 non-Hispanic white American women and 192 Chinese-American women. All women had been diagnosed with stage 0-3 breast cancer between 2006 and 2012, and they had completed primary treatment for the disease.

Data on participants' treatment side effects were gathered via telephone interview. Common side effects included menopausal symptoms — such as hot flashes and night sweats — fatigue, hair thinning, and memory problems.

A questionnaire was used to gather dietary information, and the researchers used these data to calculate the subjects' intake of soy foods — such as tofu, soy milk, and edamame — as well as cruciferous vegetables.

Soy intake among the women ranged from 0 to 431 grams per day, while intake of cruciferous vegetables ranged from 0 to 865 grams per day.

Overall, the researchers found that women with a high soy intake were 49 percent less likely to experience menopause symptoms and 57 percent less likely to experience fatigue, compared with women who had a low soy intake.

High intake of cruciferous vegetables was associated with a 50 percent lower risk of menopausal symptoms, compared with a low intake, the team reports.

Commenting on their results, the researchers write:

"In this population of breast cancer survivors, higher soy and cruciferous vegetable intake was associated with less treatment-related menopausal symptoms and fatigue."

They also identified reduced reports of hair thinning, memory problems, and joint problems among women with high intakes of soy and cruciferous vegetables, but they say that these links failed to "reach statistical significance."

Don't increase your soy intake just yet

When looking at the results by race/ethnicity, however, the scientists found that the reductions in menopausal symptoms or fatigue were only statistically significant for non-Hispanic white women.

The team speculates that this may be because Chinese women tend to report fewer menopausal symptoms and eat more cruciferous vegetables and soy, so any benefits for these foods may be more challenging to spot.

Still, Nomura and colleagues note that their findings warrant further investigation, and they say that both soy and cruciferous vegetables contain compounds that may explain their potential benefits for women who have been treated for breast cancer.

They point out, for example, that soy foods contain isoflavones, a class of phytoestrogens that can function like the female sex hormone estrogen and help to alleviate some menopausal symptoms.

But until the benefits of soy have been confirmed, the researchers recommend that people with breast cancer do not increase their intake; some research has indicated that soy might promote breast cancer.