Soy Compounds May Reduce Breast Cancer Recurrence Risk
Isoflavones, weak estrogen-like compounds found in soy, may reduce the risk of breast cancer coming back (recurrence), as well as the risk of dying from breast cancer, according to a study.
The research was published on Jan. 10, 2024, in the journal JNCI Cancer Spectrum. Read “Phytonutrients and outcomes following breast cancer: a systematic review and meta-analysis of observational studies.”
Phytonutrients are compounds produced by plants.
Why do the study?
Because isoflavones can act like a weak type of estrogen in the body, some experts have been concerned about the safety of soy foods for people who’ve been diagnosed with breast cancer. Other experts think that soy might help protect breast health because the estrogen-like strength of isoflavones is much weaker than the estrogen your body makes. The protection could come from the weaker isoflavones replacing some of your body’s stronger estrogen.
But studies on isoflavones and other plant compounds have offered mixed results. The researchers did this study to systematically review available published research to give doctors and the people they care for an analysis of the results.
About the study
This study was a meta-analysis. A meta-analysis combines and analyzes the results of many earlier studies. In this case, the researchers reviewed 22 studies that included 80,698 women that were receiving breast cancer treatment or had a history of breast cancer:
11 studies were on soy isoflavones, soy protein, or soy products
three studies were on lignans, fiber-associated compounds found in seeds, nuts, fruits, and vegetables, that also act as weak estrogens in the body
three studies were on enterolactone, a compound formed in the body when lignans are digested
three studies were on cruciferous vegetables, such as leafy greens, broccoli, and brussels sprouts
two studies were on green tea
The researchers classified the results on soy isoflavones and enterolactone as probable, which means the research showing the compounds contributed to the results was strong.
Six of the studies focused specifically on soy isoflavones. Overall, these compounds were linked to a 26% reduction in breast cancer recurrence risk.
But when the researchers accounted for the menopausal status of the women and the hormone receptor status of the breast cancer, the link was statistically significant only for post-menopausal women and estrogen receptor-positive breast cancer. So for post-menopausal women and women diagnosed with estrogen receptor-positive breast cancer, lower breast cancer recurrence risk was likely because of eating soy isoflavones and not just due to chance.
Eating 60 milligrams of soy isoflavones per day seemed to offer the most risk reduction. This is equal to two to three servings per day, where one serving is:
one cup of soy milk
three ounces of tofu
one-half cup of cooked soybeans
Enterlactone had no effect on breast cancer recurrence, but did seem to reduce the risk of post-menopausal women dying from breast cancer by 34% and from any cause by 35%. This link also was statistically significant.
The researchers said it’s not possible to figure out the most effective amount of enterolactone in someone’s diet because microbes in your gut play a role in how lignans are broken down in the body and these microbes vary among people.
The researchers classified the results on green tea, lignans, and cruciferous vegetables as suggestive, which means the results are consistent, but not strong enough to lead to recommendations.
Green tea: The two studies looking at green tea only looked to see if drinking green tea before a breast cancer diagnosis reduced the risk of recurrence. The results suggested that green tea could reduce the risk of stage I or stage II breast recurrence by 44%. There was no effect on stage III or stage IV breast cancer.
Lignans: The three studies that looked at lignans looked at the effect of eating lignans before diagnosis on survival. Post-menopausal women had a lower risk of dying from breast cancer or any cause. But in pre-menopausal women, eating lignans was linked to worse survival. Still, neither of these associations were statistically significant, and the results may have been tilted because of the results of one large study.
Cruciferous vegetables: Cruciferous vegetables seemed to have no effect on survival or recurrence, though this could be because the average amount the women ate was very low, less than one-half cup per day.
“It is critically important to stress that these studies were conducted on women who received medical and/or surgical treatment for breast cancer, and that these foods and phytonutrients should not be considered as alternatives to treatment,” senior study author Channing Paller, MD, said in a statement. Dr. Paller is director of prostate cancer clinical research and an associate professor of oncology at Johns Hopkins.
“This research highlights the need for more robust studies in this area looking at the most effective dosages of these compounds, and whether starting to consume them after diagnosis has the same effect as a lifelong dietary habit before diagnosis. This is what patients are looking for,” she added.
What this means for you
It’s important to know that while what you eat is thought to be partly responsible for roughly 30% to 40% of all cancer, diet alone is unlikely to be the cause of or a cure for cancer.
Most nutrition researchers believe that the beneficial compounds in food work together to boost your health. The benefits of any one food or compound alone have to be considered as part of your whole diet.
Instead of relying on a specific food, supplement, or vitamin, aim for a balanced diet made up of a variety of foods that includes:
five or more cups of vegetables and whole fruits per day
food from other plant sources, such as whole-grain breads and cereals, nuts, seeds, rice, and beans
Dieticians recommend nutrient-dense foods that have minimal processing. So consider fresh fruits and vegetables, whole grains, and lean meat and fish, rather than foods that have added sodium, sugar, and saturated fats.
The U.S. Department of Agriculture Dietary Guidelines for Americans, 2020-2025 recommend eating:
a variety of vegetables: dark green, red and orange, beans and peas, starchy, and others
fruits, especially whole fruits
grains, at least half of which are whole grains
fat-free or low-fat dairy, including milk, yogurt, cheese, and/or fortified soy beverages
a variety of protein foods, including seafood, lean meats and poultry, eggs, beans and peas, nuts, seeds, and soy products
oils, including oils in food, such as seafood and nuts
The guidelines also recommend:
getting less than 10% of your daily calories from sugar and saturated fat
eating fewer than 2,300 milligrams per day of sodium
drinking one or fewer alcoholic beverages per day if you’re a woman and two or fewer if you’re a man
— Last updated on March 9, 2024 at 9:42 PM