Like most other plant foods, the healthiest soy foods are the least processed. Young soybeans, also called edamame, can be steamed and eaten right from their pods. Soybeans are also used to make other foods such as soy milk, tofu, tempeh, and miso, as well as soy meats and cheeses. Examples of soy-based foods are: tofu, tempeh, miso, edamame, and soy milk. Foods made using whole soybeans like edamame, tofu, and soy milk have the most health benefits compared with more processed soy products. However, even highly processed forms of soy, such as soy protein isolate, used in soy-based meat and dairy alternatives offer more nutritional value compared with animal-based proteins.40 As much as possible, stick to simple soy products like tofu, tempeh, edamame, soy milk, or miso. These foods may help protect against cancer while providing health benefits.
Soy products offer a wide array of health benefits. Eating whole soy foods may reduce the risk of breast cancer and several other types of cancer, fibroids, and even inflammation. Soy is helpful for bone health, heart health, and menopausal symptoms.
Much of the confusion relates to phytoestrogens: these are estrogen-like compounds that occur naturally in some plants. The most common phytoestrogens are isoflavones in soy and lignans in seeds. These compounds preferentially bind to estrogen receptors in the body, which means they can have a mild estrogen effect.
Lower Risk of Breast Cancer
Research shows that women who consume soy are less likely to get breast cancer. One study found that women averaging 1 cup of soy milk or about half a cup of tofu daily have a 30% lower risk of developing breast cancer compared with women who eat little or no soy. This may be due in part to protective substances called isoflavones, a form of phytoestrogens, found in soy foods.1
In a 2013 meta-analysis that analyzed data from 22 studies, researchers found that, among Asian women, those who consumed the most isoflavones (compared with those who consumed the least) had a 32% lower risk of breast cancer.2 A protective effect was observed for both pre- and postmenopausal cancers. A 2014 meta-analysis reached similar conclusions.3 Western women don’t typically eat much soy, so it’s harder to compare between high and low levels of intake. However, eating soy foods during the preteen and teen years, when breast tissue is forming, may be especially protective.
Lower Risk of Recurrence
What about women who have been diagnosed with breast cancer? Researchers found that women diagnosed with estrogen-negative breast cancer who ate the most soy isoflavones had a 21% lower risk of dying from cancer compared with those who ate the least.7
The Women’s Healthy Eating and Living Study also showed that soy may help protect breast cancer survivors. Researchers found that women who ate the most soy cut their risk of cancer coming back or cancer death in half.8 Another study followed 5,042 women previously diagnosed with breast cancer for four years. Women who regularly consumed soy products like soy milk, tofu, or edamame came out ahead.9 They were about a third less likely to have their cancer come back and 29% less likely to die from cancer compared with women who ate little soy. Numerous other studies confirm these findings. Women who avoid soy get no advantage, while women who consume soy are less likely to have their cancer return.8,10-15
How might soy help? Soy isoflavones may help keep estrogen signaling at healthy levels. Estrogens are female hormones made by women and, to a lesser extent, men. Estrogen works by binding to “docking sites,” or receptors, on cells. When estrogen binds to its receptor, it can trigger certain cancer cells to grow. However, your cells have two different kinds of estrogen receptors: alpha and beta. Estrone, the main estrogen in women after menopause, binds mainly to the alpha receptor. Soy isoflavones preferentially bind to beta receptors. This binding seems to help block the cell growth that’s part of the cancer process.
Other Health Benefits
Soy has been found to be anti-inflammatory. In the Shanghai Women’s Health Study, researchers looked at the diet of 1,005 middle-aged Chinese women.34 The more soy products the women consumed, the less inflammation they had. Inflammation is linked to cancer, type 2 diabetes, and heart disease.
Multiple studies have found that soy protein can reduce LDL cholesterol levels.35-36 Further, soy products are free from cholesterol and contain little or no artery-clogging saturated fat.37Eating soy and other plant proteins in place of animal protein can improve heart health.
Consuming soy may also reduce the risk of hip fracture from osteoporosis. In a study published in the American Journal of Epidemiology, women who ate at least a quarter-cup of tofu per day had a 30% lower risk of fracture.38 Another study followed 75,000 postmenopausal Chinese women for three years. Researchers found that those who ate the most soy foods had a 37% lower risk of suffering a bone fracture
The Benefits of Soy
Soy has been found to be protective against developing breast cancer, particularly when consumed during adolescence. This may be because phytoestrogens affect the developing breast tissue during puberty, resulting in a reduced risk of breast cancer later in life. After a diagnosis of breast cancer, women who eat more soy-based foods actually have a better chance at a long, healthy life. They are less likely to have a recurrence and less likely to die from breast cancer than women who skip soy or eat less soy. The notion that soy products are associated with increased recurrence is a myth that has been widely and mistakenly promoted. Research findings show that eating soy foods like tofu, tempeh, and soy milk seems to have a protective effect.
The BRCA gene mutation is the most significant genetic risk factor for developing breast cancer. One study found that the protective effect of soy was stronger in women with the BRCA mutation than those without. Soy intake was associated with only a 27% breast cancer risk reduction in people without the BRCA mutation, but a 73% risk reduction in carriers of BRCA gene mutation.
Soy does NOT cause breast cancer. High soy intake is actually linked to a REDUCED risk of breast cancer and other cancers. When phytoestrogens preferentially bind to our body’s estrogen receptors, they can kick estrogen out of its binding site. This substitution results in a generally weaker estrogen effect in the body, which may be significant in preventing estrogen-sensitive breast cancers.
Soy consumption is potentially linked to reduced breast cancer recurrence. Studies have suggested that a diet high in isoflavones is linked to reduced breast cancer recurrence, thus suggesting that soy consumption is okay even in people who have previously been diagnosed with breast cancer.
Increased soy intake may be linked to improved bone health. Some studies suggest that a diet high in soy promotes improved bone health and a reduced risk of osteoporosis.
Not all soy products are equal. Highly processed soy-based products—plant-based meats and packaged foods, for example—do not provide the same health benefits and may even be harmful. Processed products generally contain high amounts of fat plus chemicals and fillers with potentially negative health effects. Products with “isolated soy protein” or “soy protein isolate” listed in the ingredients are usually highly processed and should generally be avoided.
Enjoy the benefits of 2–3 servings of soy per day
Examples of 1 serving of soy:
- 1 cup unsweetened soy milk
- ½ cup tofu / bean curd
- 3 ounces tempeh*
- 1 tablespoon miso *
- ½ cup boiled soybean
* indicates fermented soy products, which are helpful for building a healthier gut microbiome.
Plant-Based Prescription
Add 1 cup of soy milk or half a cup of tofu or edamame beans to your diet daily for the health benefits of phytoestrogens.