Some breast cancer survivors fear that eating foods containing soy will increase the risk of a cancer recurrence, but new research suggests that those worries appear to be unfounded.
The research was presented at the American Association for Cancer Research's annual meeting in Orlando, Florida.
For the study, Xiao Ou Shu, MD, PhD, a professor of epidemiology and medicine at Vanderbilt University Medical Center in Nashville, evaluated data on 9,515 women who had participated in one of three studies of breast cancer survivors.
Dr. Shu reviewed information from food questionnaires on the women's soy food intake. The average time between breast cancer diagnosis and soy food evaluation was about 14 months.
After a follow-up that averaged 7.4 years, Dr. Shu found 1,348 breast cancer recurrences and 1,171 deaths from breast cancer and other causes.
Compared with the women who ate the least soy, women in the upper 10th percentile group for soy food intake had a 35% reduced risk of recurrence
Those who ate the most soy also had a 17% reduced risk of death from all causes during the follow-up, but that finding did not reach statistical significance, Dr. Shu said.
Soy food consumption was considerably higher in the participants living in Shanghai than among the US participants.
"We did not see any evidence that soy intake after breast cancer increases the risk of recurrence or deaths (from breast cancer)," said Dr. Shu. "Our study indicated that soy food intake among breast cancer survivors is safe and may reduce the risk of recurrence," she said, referring to soy foods, such as tofu and soybeans, not soy supplements.
How much soy might be protective? "Women can get the level of soy isoflavones that is similar to the top 10% consumption level found in our US study population by consuming a cup of (soy) milk or half serving of tofu (2 oz) per day," she said.
In the past, women who survived breast cancer tended to avoid soy foods, said Marian Neuhouser, PhD, RD, associate member, cancer prevention, at the Fred Hutchinson Cancer Research Center in Seattle.
The worry, she said, was that some soy foods can act as a weak phytoestrogen (a plant chemical that can act like the hormone estrogen produced naturally in the body), and most breast cancers are estrogen-receptor positive, needing estrogen to grow.
"I think this study and a previous study support the idea that soy foods are safe for women with breast cancer," she said.
She, too, emphasized that the study focused on soy foods, not supplements.
Soy foods are a good source of low-fat protein, she said.
Soy contributes to an overall healthy diet pattern, and healthy diet patterns are linked with lower recurrence, she said.
"If someone has a latte with soy milk, it means they aren't having a latte with whole milk, which has a lot more fat in it," Dr. Neuhouser said.
Try Pomegranates to Prevent Breast Cancer!
The hormone estrogen causes certain breast cancer cells to proliferate.
Lab finding: Compounds called ellagitannins, which are plentiful in pomegranates, inhibit the aromatase enzyme that converts androgen to estrogen—and thus may help prevent the growth of hormone-dependent breast tumors. More research is needed...but in the meantime, women may benefit from adding pomegranates or pomegranate juice to their diets.