Despite its popularity.Is Soy good or bad to health?
Soybeans are a variety of legume native to Asia.
Soy has been part of traditional Asian foods for thousands of years. In fact, there’s evidence that soybeans were cultivated in China as early as 9,000 B.C.
Today, soy is widely consumed, not only as a source of plant-based protein but also as an ingredient in various processed foods.
However, soy remains a controversial food — some praise its health benefits, while others say it could be bad for you.
Wellnet Blog has gathered for you the pros and cons arising from eating soy.
Soybeans are a kind of legume that can be eaten whole or processed into a variety of forms.
Whole soy products
Whole soy products are the least processed and include soybeans and edamame, that are immature - green - soybeans. Soy milk and tofu are also made from whole soybeans.
While mature soybeans are rarely eaten whole in the Western diet, edamame is a favorite high-protein appetizer in Asian diet.
Soy milk is obtained after soaking and grinding whole soybeans, boiling them in water, and then filtering out the solids. People who cannot tolerate dairy or wish to avoid milk generally use it as a milk alternative.
Tofu is obtained by coagulating soy milk and pressing the curds into blocks. It’s a regular source of plant-based protein in vegetarian diets.
Fermented soy
Fermented soy products are processed using traditional methods such as soy sauce, tempeh, miso, and natto.
Soy sauce is a liquid condiment prepared from:
- fermented soy
- roasted grains
- salt water
- a sort of mold
Tempeh is a fermented soy cake that originated in Indonesia. Though not as popular as tofu, it’s also commonly eaten as a source of protein in vegetarian diets.
Miso is a traditional Japanese seasoning paste made from:
- soybeans
- salt
- a type of fungus
Soy-based processed foods
Soy is used to make various processed foods, including:
- vegetarian and vegan meat substitutes
- yogurts
- cheeses
Many packaged foods have soy flours, texturized vegetable protein, and soybean oil.
Soy supplements
Soy protein isolate is a highly processed derivative of soy obtained by grinding soybeans into flakes and extracting the oil.
The flakes are then mixed with alcohol or alkaline water, heated, and the obtained soy concentrate is spray-dried into a powder.
Soy protein isolate is available in different protein powders and also added to many processed foods, like protein bars and shakes.
Other soy supplements such as soy isoflavones, which are available in capsule form, and soy lecithin, which can be absorbed in capsules or as a powder.
Soy foods are a good source of many essential nutrients.
For instancee, 1 cup (155 grams) of edamame contains:
- Calories: 189
- Carbs: 11.5 grams
- Protein: 16.9 grams
- Fat: 8.1 grams
- Fiber: 8.1 grams
- Vitamin C: 16% of the Reference Daily Intake (RDI)
- Vitamin K: 52% of the RDI
- Thiamine: 21% of the RDI
- Riboflavin: 14% of the RDI
- Folate: 121% of the RDI
- Iron: 20% of the RDI
- Magnesium: 25% of the RDI
- Phosphorus: 26% of the RDI
- Potassium: 19% of the RDI
- Zinc: 14% of the RDI
- Manganese: 79% of the RDI
- Copper: 19% of the RDI
Soy also supplies small amounts of
vitamin E, niacin, vitamin B6, and pantothenic acid.
Moreover, it contains prebiotic fiber and many beneficial phytochemicals,such as lant sterols and the isoflavones daidzein and genistein.
The unique phytochemicals in soy can offer numerous health advantages:
Might help lower cholesterol
Various studies suggest that soy may improve cholesterol levels,and reduce 9 LDL (bad) cholesterol.
In an extensive review of 35 studies, researchers discovered that eating soy products reduced LDL (bad) cholesterol and total cholesterol while raising HDL (good) cholesterol.
These improvements were higher in /people with high cholesterol levels
However, the researchers observed that soy supplements didn’t possess the same cholesterol-lowering effect as eating soy foods.l
In another older review of 38 studies, researchers observed that an average soy intake of 47 grams per day could lead to a 9.3% decrease in total cholesterol and a 13% decrease in LDL (bad) cholesterol.
It seems to play an essential role in cholesterol-lowering effects of soy.
In one study, 121 adults with high cholesterol consumed 25 grams of soy protein with or without soy fiber for 8 weeks. The soy with fiber reduced LDL (bad) cholesterol more than two times as much as soy protein alone.
Might affect fertility
Studies have released conflicting results on the connection between soy intake and fertility.
For instance, one study revealed that soy consumption was associated with improved outcomes for women undergoing fertility treatments with assisted reproductive technology
Another study demonstrated that soy had a protective effect against BPA, a chemical found in plastic, which may affect fertility negatively.
Women who ate soy before in vitro fertilization (IVF) were more likely to experience a successful pregnancy than those who did not
Furthermore, soy intake by the prospective father does not seem to influence pregnancy rates in women receiving IVF
On the other hand, some studies have discovered that soy intake may actually negatively affect fertility.
For instance, one review reported that consuming very high quantity of soy could alter levels of reproductive hormones and negatively impact on ovarian function
Another study in 11,688 women found that higher soy isoflavone intake could lead to a lower likelihood of having been pregnant or giving birth to a live child.
What’s more, an animal study showed that feeding rats a diet rich in soy phytoestrogens induced a number of symptoms of polycystic ovary syndrome (PCOS), which could negatively affect reproductive health
Therefore, more research is needed to examine the complex relationship between soy consumption and fertility.
Might reduce menopause symptoms
Isoflavones are a class of phytoestrogens discovered naturally in soy that act like a weak estrogen in the body.
Estrogen levels decrease during menopause, leading to symptoms such as hot flashes. Since soy acts as a natural estrogen, it can help reduce these symptoms.
Studies indicate soy’s beneficial role in menopause.
In a review of 35 studies, soy isoflavone supplements increased estradiol (estrogen) levels in postmenopausal women by 14%
Lastly, in another review of 17 studies, women who absorbed an average dose of 54 mg of soy isoflavones a day for 12 weeks had 20.6% fewer hot flashes.
They also experienced a 26.2% decrease in symptom severity compared to that at the start of the study
While soy has numerous health benefits, its impact on other conditions is not yet clear.
Effect on breast cancer not yet proven
Soy has isoflavones, which act like estrogen in the body. Since many breast cancers need estrogen to
grow, it would stand to reason that soy may increase breast cancer risk.
However, this isn’t confirmed in most studies.
In fact, according to one review, higher soy intake may be attributed to a 30% lower risk of developing breast cancer in Asian women
However, for women in Western countries, one study revealed that soy intake had no effect on the risk of developing breast cancer
This difference may be due to the various types of soy eaten in the Asian diet compared to the Western diet.
Soy is typically consumed whole or fermented in Asian diets, whereas in Western countries, soy is essentially processed or in supplement form.
One review noted that soy isoflavones undergo structural changes during the fermentation process, which could significantly increase absorption
In addition, an animal study also revealed that fermented soy milk was more effective than regular soy milk at suppressing the growth and spread of breast cancer tumor cells in rats
Therefore, fermented soy could have a more protective effect against breast cancer compared to many processed soy products.
In addition to protecting against breast cancer development, soy has also been attributed to a longer lifespan after breast cancer diagnosis.
In a review of five long-term studies, women who took soy after diagnosis were 21% less likely to have a recurrence of cancer and 15% less likely to die than women who didn’t take soy.
Effect on thyroid function
Soy contains goitrogens, substances that may negatively affect the thyroid by blocking iodine absorption.
Some research has found that some soy isoflavones, including genistein, could block the production of thyroid hormones. However, these findings are mostly around test-tube and animal studies.
On the other hand, studies on the impact of soy on thyroid function in humans indicate it may not have a significant effect.
One review of 18 studies showed that soy supplementation had no effect on thyroid hormone levels.
Although it slightly increased levels of thyroid stimulating hormone (TSH), it’s not clear whether this is important for those with hypothyroidism.
However, according to another previous review of 14 studies, soy had little to no effect on thyroid function.
The authors concluded that people with hypothyroidism do not need to stay away from soy as long as their iodine intake is adequate.
Furthermore, another randomized trial discovered that consuming 66 mg a day of soy phytoestrogens had no effect on thyroid function in 44 people with subclinical hypothyroidism.
Impact on male sex hormones
Because soy contains phytoestrogens, men may worry about adding it in their diet.
However, studies do not indicate that soy has negative impacts on the production of testosterone in men.
In a review of 15 studies in men, intake of soy foods, protein powders, or isoflavone supplements up to 70 grams of soy protein and 240 mg of soy isoflavones per day did not modify free testosterone or total testosterone levels
What’s more, soy could reduce the risk of prostate cancer in men.
In a review of 30 studies, high soy consumption was attributed to a significantly lower risk of developing the disease.
Some studies have suggested that soy could have some positive effects on cholesterol levels, cancer risk, and menopause symptoms.
However, other studies have demonstrated that soy intake may negatively impact certain aspects of health, such as digestion and ovarian function.
What’s more, research has indicated that the potential health benefits of soy depend on the form in which it’s consumed, with whole or fermented soy foods being more beneficial than processed forms of soy.
Although it’s clear that more high-quality research is needed to determine the effect of soy consumption on overall health, the majority of current studies suggest that consuming whole or fermented soy foods in moderation is likely safe and beneficial for most people.
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