Soybeans are a type of legume native to East Asia. It is an important ingredient in Asian diets and has been consumed for thousands of years.
Today, they are mainly grown in Asia and South and North America. In Asia, soybeans are often eaten whole, but heavily processed soy products are more common in Western countries.
Various soybean products are available, including:
- Soy flour
- Soy protein
- Tofu
- Soy milk
- Soy sauce
- Soybean oil
Soybeans contain antioxidants and phytonutrients that are associated with various health benefits.
However, concerns have been raised about possible adverse effects. This article tells you everything you need to know about soybeans.
Soybean nutrients
Soybeans are mainly made up of protein but also contain good amounts of carbohydrates and fats.
The nutritional facts for 3.5 servings (100 grams) of boiled soybeans are (s):
1- Calories: 173
2- Water: 63%
3- Protein: 16.6 grams
4- Carbs: 9.9 grams
5- Sugar: 3 grams
6- Fiber: 6 grams
7- Fat: 9 grams
- Saturated: 1.3 grams
- Monounsaturated: 1.98 grams
- Polyunsaturated: 5.06 g
- Omega 3: 0.6 grams
- Omega 6: 4.47 grams
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Health benefits of soybeans
Like most whole foods, soybeans have a number of beneficial health effects.
1. May reduce the risk of cancer
Cancer is one of the leading causes of death in modern society. Eating soy products is associated with an increase in breast tissue in women, which hypothetically leads to an increased risk of breast cancer (s, s, s).
However, most observational studies suggest that consumption of soy products may reduce the risk of breast cancer (s, s).
Studies also indicate a protective effect against prostate cancer in men (s, s, s).
A number of soybean compounds - including isoflavones and lunasin - may be responsible for their potential cancer protective effects (s, s).
Exposure to isoflavones early in life may be particularly protective against breast cancer later in life (s, s).
Keep in mind that this evidence is limited to observational studies, which suggest an association between soy consumption and cancer prevention — but do not prove causation.
2. Reducing the symptoms of menopause
Menopause is the period in a woman's life when menstruation stops. It is often associated with unpleasant symptoms — such as sweating and mood swings — that are caused by low estrogen levels.
Interestingly, Asian women - especially Japanese - are less likely to have menopausal symptoms than Western women. Dieting habits, such as the increased consumption of soy foods in Asia, may explain this difference.
Studies show that isoflavones, a family of phytoestrogens found in soybeans, may relieve these symptoms (s, s).
Soy products do not affect all women in this way. Soy appears to be effective only in so-called equol producers - those who possess a type of gut bacteria capable of converting isoflavones into equol. Equol may be responsible for many of the health benefits of soybeans.
Taking 135 mg of isoflavones per day for one week - the equivalent of 2.4 servings (68 grams) of soybeans per day - reduced menopausal symptoms only in Ecol products (s).
While hormonal therapies have traditionally been used as a treatment for menopausal symptoms, isoflavones supplements are widely used today.
3. May help bone health
Osteoporosis is characterized by low bone density and an increased risk of fractures, especially in older women.
Consumption of soy products may reduce the risk of osteoporosis in women who have gone through menopause (s, s). These beneficial effects are due to isoflavones (s, s, s).
Bottom Line: Soybeans contain plant compounds that may help prevent breast and prostate cancer.
Furthermore, these legumes may relieve menopausal symptoms and reduce the risk of osteoporosis in postmenopausal women.
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Soybean side effects
Although soybeans have a number of health benefits, some individuals need to limit their consumption of soy products - or avoid them altogether.
1- Suppression of thyroid function
Eating large amounts of soy products may suppress thyroid function in some people and contribute to hypothyroidism - a condition characterized by underproduction of thyroid hormones (s).
The thyroid is a large gland that regulates growth and controls the rate at which the body spends energy.
Animal and human studies suggest that the isoflavones in soybeans may inhibit the formation of thyroid hormones (s, s).
One study in 37 Japanese adults showed that eating 1 serving (30 grams) of soybeans daily for 3 months caused symptoms related to suppressed thyroid function.
Another study in adults with mild hypothyroidism found that taking 16 mg of isoflavones every day for two months impaired thyroid function in 10% of participants (s).
The amount of isoflavones consumed was rather small - the equivalent of eating 0.3 ounces (8 grams) of soybeans per day (s).
However, most studies in healthy adults have not found any significant links between soy consumption and changes in thyroid function (s, s, s).
An analysis of 14 studies noted no significant adverse effects of soy consumption on thyroid function in healthy adults, while children born with deficient thyroid hormone were considered to be at risk (s).
In short, regular consumption of soy products or isoflavone supplements may lead to hypothyroidism in sensitive individuals, especially those with an underactive thyroid.
2- Flatulence and diarrhea
Like most other types of beans, soybeans contain insoluble fiber, which may cause flatulence and diarrhea in sensitive individuals (s, s). Although these side effects are not harmful to health, they can be bothersome.
Belonging to a class of fibers called FODMAPs, raffinose and stachyose may exacerbate symptoms of IBS, a common digestive disorder (s).
If you have IBS, it may be a good idea to avoid or limit your soy intake.
3- Soy allergy
Food allergy is a common condition caused by an adverse immune reaction to certain ingredients in foods.
Soy allergy is triggered by the soy proteins - glycinin and conglycinin - found in most soy products (s).
Although soybeans are one of the most common food allergens, soy allergy is relatively uncommon in both children and adults (s, s).