Soy and its relationship with breast cancer

About soy

Soy is a well-known Asian legume. Vegetarians frequently use soy to replace meat in their diets. Soybeans are nutritious and high in protein, offering them a wide range of nutritional benefits. People can eat them, drink them as milk substitutes, and consume them as supplements. They belong to the pea family. Soybeans come in a variety of colors, including:

  • Green soybeans: Edamame is another name for young green soybeans. People can boil them and have them as a snack right out of the pod. Shelled edamame can be used in salads, stir-fries, and soups.
  • Yellow soybeans: Yellow soybeans are commonly used in the manufacture of soy milk, tofu, tempeh. They also contribute to the manufacture of soy flour for baking.
  • Black soybeans: In traditional Asian cuisines, black soybeans are boiled or fermented. 

For individuals wishing to replace dairy in their diet, soy milk and cheese are also choices. Soybeans can yield soy oil, which can be used in cooking or as an additive. After extracting the oil from soybeans, the residual material can be used to manufacture feed for farm animals and pets. Soy is used by certain producers to manufacture protein powder and isoflavone supplements. Isoflavones are plant chemicals with a structure similar to estrogen. Organic soy that has been processed as little as possible is the healthiest alternative. Here are several examples:

  • Cooked soybeans 
  • Edamame
  • Tempeh
  • Flavored and unflavored soy milk
  • Tofu 
  • Soy nuts 

Nutritional value of soy

Soy is indeed a complete protein source. It includes all nine essential amino acids, hence it is complete. For several people, particularly those who practice a vegan or vegetarian diet, it is a significant source of protein for them. The United States Department of Agriculture (USDA) reports that 100 grams (g) of cooked green soybeans without salt contain:  

  • 141 kilocalories.
  • 12.35gm protein. 
  • 6.4gm fat. 
  • 11.05gm carbohydrates. 
  • 4.2gm fiber. 

Soybeans are full of protein, vitamin C, and folate while being low in saturated fat. They are also high in calcium, iron, magnesium, phosphorus, potassium, and thiamin.  

Potential health benefits

Diets that are high in soy have been linked to a number of potential health benefits, including: 

1.) May help reduce cholesterol levels.

Several studies suggest that soy-rich diets may help decrease LDL (bad) cholesterol while increasing HDL (good) cholesterol. According to one recent study, a daily intake of 25 grams of soy protein may significantly minimize total and LDL (bad) cholesterol levels by approximately 3%. Individuals who already have risk factors for cardiovascular disease, such as high cholesterol, obesity, or type 2 diabetes, tend to benefit the most from soy-rich diets. Furthermore, minimally processed soy products like soybeans, tofu, tempeh, and edamame seem to lower cholesterol levels more than processed soy products and supplements

2.) May reduce blood sugar.

According to one analysis of 17 randomized controlled trials, soy isoflavones may help marginally lower blood sugar and insulin levels in menopausal women. Soy isoflavones may also aid in the reduction of insulin resistance, a state in which cells no longer respond appropriately to insulin. Insulin resistance can lead to elevated blood sugar levels and type-2 diabetes over time. Furthermore, there is some evidence that soy protein supplements may assist individuals with type 2 diabetes or metabolic syndrome lower their blood sugar and insulin levels considerably.

3.) May lower blood pressure.

Soybeans and products prepared from them are high in arginine, an amino acid that is known to help manage blood pressure levels. Soybeans are also high in isoflavones, another component thought to have blood pressure-lowering properties. Certain studies relate regular soy isoflavone intakes of 65–153 mg to blood pressure decreases of 3–6 mm Hg in patients with high blood pressure.

4.) May help lower the risk of cancers

Diets high in soy may also help reduce the incidence of cancer. For example, research indicates that consuming a lot of soy isoflavones may lower the risk of endometrial cancer by about 19% (Zhong et al., 2018). Furthermore, some research has connected soy-rich diets to a 7% lower risk of gastrointestinal tract malignancies and an 8–12% lower risk of colon and colorectal cancers, particularly in women. Men who consume soy-rich diets, on the other hand, may have a lowered risk of prostate cancer. Furthermore, a recent assessment of 23 trials connected soy-rich diets to a 13% decreased chance of dying from cancer, notably stomach, large intestine, and lung cancer.

Soy and breast cancer

Soy foods were long thought to raise the risk of breast cancer. Consuming a reasonable amount of soy foods, on the other hand, does not increase the risk of developing breast cancer – or any other sort of cancer. A reasonable amount is one to two servings of whole-soy meals including tofu, soy milk, and edamame per day.

So, how did the notion that soy raises the risk of breast cancer emerge? Soy contains isoflavones, which are plant estrogens. Elevated oestrogen concentrations have been related to an increased risk of breast cancer. The phrase “phytoestrogens” causes confusion about soy. These isoflavones contain molecular structures that resemble estrogen, which is found in a woman’s body and functions similarly to human oestrogen but with far lesser effects. This is where the term phytoestrogen came from. Phytoestrogens, on the other hand, are not the same as female estrogens. Therefore, whole soy foods have no estrogen and cannot raise the risk of breast cancer. A continuous stream of research demonstrated that a soy-rich diet did not increase the risk of developing breast cancer and may even lower it.

Soy-rich diets have also been related to a reduced risk of some cancers. For example, a recent analysis of 12 studies reveals that women who consume a lot of soy before getting a cancer diagnosis may have a 16% reduced risk of dying from the disease than those who consume the least amount. Another study reveals that premenopausal and postmenopausal women who eat soy-rich diets may have a 27% decreased risk of cancer. According to a 2019 review of studies, isoflavones found in soy can help reduce the incidence of hormone-related cancers such as prostate cancer and some breast cancers.

In one study of over 73,000 Chinese women, researchers discovered that all those who consumed at least 13 grams of soy protein per day, equivalent to one to two servings, were 11% less prone to get breast cancer than those who consumed less than 5 grams. The findings are encouraging, but there is still insufficient information. Experts now believe that soy isoflavones may actually prevent estrogen from adhering to breast cancer cells rather than stimulating growth, as previously believed.

Researchers reviewed data from dietary surveys completed by over 9,500 American and Chinese women in one study. Those who reported they ate the most soy were 25% less prone to have their cancer recur than those who reported they ate the least. The study considered tofu, soy milk, and fresh soybeans as soy foods. As one might assume, Chinese women ate significantly more of it than those in the United States. When the researchers took it into account, the results still remained consistent. Some of these findings also imply that breast cancer survivors who eat soy foods have a reduced risk of recurrence than survivors who avoid soy.


Diets high in soy may benefit heart health by lowering blood pressure, blood sugar, and cholesterol levels. They may also boost fertility, alleviate menopausal symptoms, and protect against some cancers. More research, though, is required. Whole soy foods are safe to consume as part of a healthy balanced diet. Soy and whole soy products can definitely be a part of an anti-cancer diet or cancer prevention diet. 

Soy foods are indeed a healthy choice, but soy nutritional supplements are not. Soy foods, and not dietary supplements, have been studied in relation to soy and breast health. Soy or isoflavone supplements, on the contrary, have greater levels of isoflavones. Some research has indicated a link between soy or isoflavone supplements and an elevated risk of breast cancer in women with a family or personal history of breast cancer or thyroid issues.