Why We Use (and Love!) Soy

In case you haven’t heard, soy is in (ref, ref). First cultivated for food in Asia in 1100 BC (and perhaps even earlier), soybeans (Glycine max) have been widely consumed around the world in various forms for centuries. Common soy foods include whole soybeans (edamame), soy milk, tofu, and fermented soy products like soy sauce, miso, and tempeh. Soy-derived products also include ingredients like soy oil, the most commonly consumed cooking oil in the US (ref).; soy lecithin, a fatty substance commonly used in food mixtures; and soy protein concentrate, a source of protein in a wide variety of foods, like nutrition bars and plant-based meat alternatives.

At Impossible Foods, we use soy protein in our products because it is a nutrient powerhouse and, in combination with some other ingredients, it helps make our meat chew like, well, meat. Read on to learn more!

Nutritional Benefits of Soy

Nutritionally, soy stands out as a great source of protein. This is due not only to the total amount of protein in soy, but also to the high quality of the protein it contains. The method most commonly used to define “protein quality” is Protein Digestibility Corrected Amino Acid Score (PDCAAS), which assesses a protein’s essential amino acid content as well as its digestibility, with a “perfect” score being 1 (ref). Soy foods have PDCAAS values ranging from 0.91 to 1 (ref, ref, ref), and soy protein concentrate has a published PDCAAS value of 0.99 (ref). For reference, the PDCAAS of beef from cows is 0.92 (ref). Soy protein thus stands out among other plant-based proteins, and its protein quality matches that of animal-based proteins (ref).

In addition to containing high quality protein, soy is rich in many other beneficial nutrients, including dietary fiber - for example, 3.5oz (100g) of cooked soybeans contains 6g dietary fiber, which is 21% of the daily value for fiber (ref). Soy is also a good source of polyunsaturated fatty acids (the good kind of fats!) and many essential vitamins and minerals, including iron, potassium, calcium, and folate (ref).

Over 2000 studies are published annually (ref, ref) that examine various health implications of soy intake, and scientists widely recognize its benefits. Clinical research since the 1960s has shown soy to have at least a modest lowering effect on cardiovascular disease risk factors, such as LDL-cholesterol levels and blood pressure (ref, ref, ref, ref). Other health benefits associated with soy include improved bone health (ref, ref, ref, ref), possible alleviation of menopausal symptoms (ref, ref, ref), and reduced risk for breast (ref, ref) and prostate (ref) cancers. Recent research has even suggested that soy can support skin health and appearance in post-menopausal women, reducing skin wrinkles and increasing skin hydration (ref)!

Soy is a source of phytonutrients, which are natural compounds produced by plants as part of their defense against infections and damage. Phytonutrients also play a role in human health through their anti-inflammatory and antioxidant functions in the body (ref). Soy is high in a class of antioxidant phytonutrients called isoflavones, which is thought to be the source of many of soy foods’ proposed health benefits.

Myths about Soy: What Does The Science Say?

Despite the nutrient density and potential health benefits of consuming soy, myths persist. A common misconception is concern that soy can cause estrogen-like effects in humans. This is because soy isoflavones are structurally similar to the primary female sex hormone, 17-β-estradiol, and have been shown in in vitro tests to bind estrogen receptors (ERs), where they may exert mild estrogen promoting and/or blocking effects. It’s important to note that the isoflavones actually preferentially bind to one type of estrogen receptor, ER ß, which appears to be associated with anti-proliferative, anti-carcinogenic (i.e., cancer-protective) effects (ref). Nevertheless, the fact that isoflavones can bind to estrogen receptors has still raised concerns among some that they can negatively affect human health. Let’s dig a little deeper into what the science says:

Myth #1: “Soy is linked to developing or worsening breast cancer”

As noted earlier, epidemiological scientific evidence actually suggests that soy intake may be protective against the development of breast cancer (ref). Historically low rates of breast cancer among the countries with the highest soy consumption contributes to the speculation that soy, particularly isoflavones, offers protection against breast cancer (ref), and the scientific evidence supports this (ref, ref). One leading hypothesis for the protective effects of soy posits that isoflavone-rich soy consumption during childhood and adolescence reduces risk for breast cancer development later in life – a hypothesis known as the “early intake hypothesis,” which has gained support from both animal and epidemiological studies (ref, ref, ref, ref).

There is also concern about soy intake and prognosis in post-diagnosis breast cancer patients, largely stemming from a series of mouse studies in the 1990s that raised concern that isoflavone-containing soy foods may worsen the prognosis of women who have been diagnosed with breast cancer (ref, ref). However, humans are not rodents (ref) and clinical human studies have consistently shown that neither soy nor isoflavones impact markers of breast cancer risk, like breast tissue density (ref, ref) and breast cell proliferation (ref, ref). Furthermore, a recent meta-analysis of observational studies also concluded that isoflavones may significantly reduce the risk of breast cancer recurrence or death (ref); in the review, the authors found that soy isoflavones were associated with a 26% reduced risk of breast cancer recurrence. Leading health agencies around the world, including the American Cancer Society (ref), Academy of Nutrition and Dietetics Oncology Group (ref), and the Canadian Cancer Society (ref), have also concluded that breast cancer patients can safely consume soy foods containing isoflavones.

Myth #2: “Soy causes male feminization

The fact that soy isoflavones are phytoestrogens has caused some to be concerned that soy can cause estrogen levels to increase in men. However, clinical studies have shown that neither soy nor isoflavones affect hormone (testosterone and estrogen) levels in men, even when the amount of soy protein or isoflavone supplements consumed in these studies greatly exceeded typical dietary intake (ref, ref, ref, ref). Studies have also found no consistent association between soy intake and parameters of male fertility, such as sperm concentration and motility (ref, ref).

There has been one published case study describing a 60 year old male who developed gynecomastia (benign enlargement of the breasts, sometimes referred to as “man boobs”) after consuming 3 quarts of soy milk daily over a significant period of time (ref). Case reports, while important and interesting, should never be the basis for scientific conclusions; in this case, the amount of soy milk consumed by the individual severely exceeded typical amounts consumed by men in Asian countries, where intakes of soy are higher than in western countries (ref). At levels of intake that high, it is likely that other health complications, more serious than the benign enlargement of the breast tissue, would arise and be the cause for discontinuation of such a diet. In 2020, another unusual case report was published describing gynecomastia in an 8-year-old boy who consumed excessive amounts of soy (ref). In this case, the authors conclude that there may be rare individuals who are abnormally sensitive to phytoestrogens but that these individuals can avoid undesirable effects like gynecomastia by simply limiting their intake of soy.

Myth #3: “Soy is bad for kids”

Intake of soy among children and adolescents is not new; in fact, soy has served as a part of the traditional diet for kids in many Asian countries for centuries! Soy, with its high protein quality, dietary fiber, and essential micronutrients (nutrients that are currently under-consumed by children in the US (ref)), fits the bill as a nutritional powerhouse during childhood, a period important for not only physical growth but also for formation of healthy dietary habits that can last into adulthood (ref).

Because of the isoflavone content of soy foods, some may be concerned about the potential for soy foods to affect hormone levels during childhood, with particular interest in the potential for soy to cause earlier onset of puberty in both girls and boys. However, the scientific evidence suggests that soy does not exert adverse hormonal effects in children or affect pubertal development (ref, ref). In fact, many studies have looked at the effects of soy infant formula and concluded that consumption of soy intake formula as an infant is not associated with earlier onset of puberty compared with infants who consumed cow's milk based formulas (ref, ref).

A Note on Soy Allergy

In the US, soy is one of “the Big 9” allergens (ref), meaning that it is considered common enough to require labeling on a food package. However, according to studies published in 2018 and 2019, the prevalence of soy allergy is much lower than that of other common food allergies (ref). Typically, symptoms of soy allergy are mild, but in some cases can be severe (i.e. cause anaphylaxis), so individuals allergic to soy should avoid consuming soy protein and may be advised by their allergist or doctor to also avoid foods made using other soy-based ingredients. Fortunately, soy allergies are often outgrown. Current research suggests that over 70% of children with a diagnosed soy allergy develop tolerance by the time they are 10 years old (ref). For more information on food allergies as well as the allergenicity of Impossible Foods’ products, see our blog here.

Conclusion

Soy and soy foods serve as safe and nutritious options that can easily be incorporated into a well-rounded, health-promoting diet. Whether you’re looking for vegetarian or flexitarian meal options or simply want to add variety to your meals with Meatless Mondays, there are many delicious traditional dishes that use soy, and now, Impossible Foods makes it even easier to incorporate this nutritional powerhouse into your diet!