Soybeans, a potent source of plant-based protein, offer other beneficial plant compounds. They may reduce your risk of cancer and alleviate menopause symptoms, but excessive consumption may cause digestive problems.
Soybeans or soya beans (Glycine max) are a type of legume native to eastern Asia.
They are an important component of Asian diets and have 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 much more common in Western countries.
Various soy products are available, including soy flour, soy protein, tofu, soy milk, soy sauce, and soybean oil.
Soybeans contain antioxidants and phytonutrients that are linked to various health benefits. However, concerns have been raised about potential adverse effects.
This article tells you everything you need to know about soybeans.
Share on PinterestDiane Labombarbe/Getty ImagesNutrition facts
Soybeans are mainly composed of protein but also contain good amounts of carbs and fat.
The nutrition facts for 3.5 ounces (100 grams) of boiled soybeans are (1):
- Calories: 172
- Water: 63%
- Protein: 18.2 grams
- Carbs: 8.4 grams
- Sugar: 3 grams
- Fiber: 6 grams
- Fat: 9 grams
- Saturated: 1.3 grams
- Monounsaturated: 1.98 grams
- Polyunsaturated: 5.06 grams
Protein
Soybeans are among the best sources of plant-based protein.
The protein content of soybeans is 36–56% of the dry weight (2, 3, 4).
One cup (172 grams) of boiled soybeans boasts around 31 grams of protein (1).
The nutritional value of soy protein is very good, although the quality is not quite as high as some animal proteins (5, 6).
The main types of protein in soybeans are glycinin and conglycinin, which make up approximately 80% of the total protein content. These proteins may trigger allergic reactions in some people (4, 7).
Consumption of soy protein has been linked with a modest decrease in cholesterol levels (8, 9, 10).
Fat
Soybeans are classified as oilseeds and used to make soybean oil.
The fat content is approximately 18% of the dry weight — mainly polyunsaturated and monounsaturated fatty acids, with small amounts of saturated fat (11).
The predominant type of fat in soybeans is linoleic acid, accounting for approximately 50% of the total fat content.
Carbs
Being low in carbs, whole soybeans are very low on the glycemic index (GI), which is a measure of how foods affect the rise in blood sugar after a meal (12).
This low GI makes soybeans suitable for people with diabetes.
Fiber
Soybeans contain a fair amount of both soluble and insoluble fiber.
The insoluble fibers are mainly alpha-galactosides, which may cause flatulence and diarrhea in sensitive individuals (13, 14).
Alpha-galactosides belong to a class of fibers called FODMAPs, which may exacerbate the symptoms of irritable bowel syndrome (IBS) (15).
Despite causing unpleasant side effects in some people, soluble fibers in soybeans are generally considered healthy.
They are fermented by bacteria in your colon, leading to the formation of short-chain fatty acids (SCFAs), which may improve gut health and reduce your risk of colon cancer (16, 17).
SUMMARYSoybeans are a very rich source of plant-based protein and fat. What’s more, their high fiber content is good for your gut health.
Vitamins and minerals
Soybeans are a good source of various vitamins and minerals, including (1):
- Molybdenum. Soybeans are rich in molybdenum, an essential trace element primarily found in seeds, grains, and legumes (18).
- Vitamin K1. The form of vitamin K found in legumes is known as phylloquinone. It plays an important role in blood clotting (19).
- Folate. Also known as vitamin B9, folate has various functions in your body and is considered particularly important during pregnancy (20).
- Copper. Dietary intake of copper is often low in Western populations. Deficiency may have adverse effects on heart health (21).
- Manganese. A trace element found in most foods and drinking water. Manganese is poorly absorbed from soybeans due to their high phytic acid content (22).
- Phosphorus. Soybeans are a good source of phosphorus, an essential mineral abundant in the Western diet.
- Thiamine. Also known as vitamin B1, thiamine plays an important role in many bodily functions.
Soybeans are a good source of several vitamins and minerals, including vitamin K1, folate, copper, manganese, phosphorus, and thiamine.
Other plant compounds
Soybeans are rich in various bioactive plant compounds, including (23, 24, 25, 26):
- Isoflavones. A family of antioxidant polyphenols, isoflavones have a variety of health effects.
- Phytic acid. Found in all plant seeds, phytic acid (phytate) impairs the absorption of minerals like zinc and iron. Levels of this acid can be reduced by boiling, sprouting, or fermenting the beans.
- Saponins. One of the main classes of plant compounds in soybeans, saponins have been found to reduce cholesterol in animals.
Isoflavones
Soybeans contain higher amounts of isoflavones than other common foods (27).
Isoflavones are unique phytonutrients that resemble the female sex hormone estrogen. In fact, they belong to a family of substances called phytoestrogens (plant estrogens).
The main types of isoflavones in soy are genistein (50%), daidzein (40%), and glycitein (10%) (23).
Some people possess a special type of gut bacteria that can convert daidzein to equol, a substance considered responsible for many of the beneficial health effects of soybeans.
People whose bodies can produce equol are expected to benefit much more from soy consumption than those whose bodies cannot (28).
The percentage of equol producers is higher in Asian populations and among vegetarians than in the general Western population (29, 30).
SUMMARYSoybeans are a rich source of various bioactive plant compounds, including isoflavones, saponins, and phytic acid. Isoflavones in particular mimic estrogen and are responsible for many of soybeans’ health effects.
Health benefits of soybeans
Like most whole foods, soybeans have a number of beneficial health effects.
May reduce cancer risk
Cancer is one of the leading causes of death in modern society.
Eating soy products is linked to increased breast tissue in women, hypothetically increasing the risk of breast cancer (31, 32, 33).
However, most observational studies indicate that consumption of soy products may reduce breast cancer risk (34, 35).
Studies also indicate a protective effect against prostate cancer in men (36, 37, 38).
A number of soybean compounds — including isoflavones and lunasin — may be responsible for the potential cancer-preventive effects (39, 40).
Exposure to isoflavones early in life may be particularly protective against breast cancer later in life (41, 42).
Keep in mind that this evidence is limited to observational studies, which indicate an association between soy consumption and cancer prevention — but do not prove causation.
Alleviation of menopause symptoms
Menopause is the period in a woman’s life when menstruation stops.
It is often associated with unpleasant symptoms — such as sweating, hot flashes, and mood swings — which are brought about by a reduction in estrogen levels.
Interestingly, Asian women — especially Japanese women — are less likely to experience menopause symptoms than Western women.
Dietary habits, such as the higher consumption of soy foods in Asia, may explain this difference.
Studies indicate that isoflavones, a family of phytoestrogens found in soybeans, may alleviate these symptoms (43, 44).
Soy products do not affect all women in this way. Soy only seems to be effective in so-called equol producers — those who possess a type of gut bacteria able to convert isoflavones into equol.
Equol may be responsible for many of soy’s health benefits.
Daily intake of 135 mg of isoflavones for 1 week — equivalent to 2.4 ounces (68 grams) of soybeans per day — reduced menopausal symptoms only in equol producers (45).
While hormonal therapies have traditionally been used as a treatment for menopausal symptoms, isoflavone supplements are widely used today (46).
Bone health
Osteoporosis is characterized by reduced 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 undergone menopause (47, 48).
These beneficial effects seem to be caused by isoflavones (49, 50, 51, 52).
SUMMARYSoybeans contain plant compounds that may help prevent breast and prostate cancer. What’s more, these legumes may relieve menopause symptoms and cut the risk of osteoporosis in postmenopausal women.
Concerns and adverse effects
Even though soybeans have a number of health benefits, some individuals need to limit their consumption of soy products — or avoid them altogether.
Suppression of thyroid function
High intake of soy products may suppress thyroid function in some people and contribute to hypothyroidism — a condition characterized by low production of thyroid hormones (53).
The thyroid is a large gland that regulates growth and controls the rate at which your body expends energy.
Animal and human studies indicate that the isoflavones found in soybeans may suppress the formation of thyroid hormones (54, 55).
One study in 37 Japanese adults showed that eating 1 ounce (30 grams) of soybeans every day for 3 months caused symptoms related to suppressed thyroid function.
The symptoms included discomfort, sleepiness, constipation, and thyroid enlargement — all of which disappeared after the study ended (56).
Another study in adults with mild hypothyroidism found that taking 16 mg of isoflavones every day for 2 months suppressed thyroid function in 10% of the participants (55).
The amount of isoflavones consumed was rather small — equivalent to eating 0.3 ounces (8 grams) of soybeans per day (57).
However, most studies in healthy adults have not found any significant links between soy consumption and changes in thyroid function (58, 59, 60).
An analysis of 14 studies noted no significant adverse effects of soybean consumption on thyroid function in healthy adults, whereas infants born with thyroid hormone deficiency were considered at risk (58).
In short, regular consumption of soy products or isoflavone supplements may lead to hypothyroidism in sensitive individuals, especially those who have an underactive thyroid gland.
Flatulence and diarrhea
Like most other beans, soybeans contain insoluble fibers, which may cause flatulence and diarrhea in sensitive individuals (13, 14).
Although not unhealthy, these side effects can be unpleasant.
Belonging to a class of fibers called FODMAPs, the fibers raffinose and stachyose may worsen symptoms of IBS, a common digestive disorder (15).
If you have IBS, avoiding or limiting the consumption of soybeans may be a good idea.
Soy allergy
Food allergy is a common condition caused by a harmful immune reaction to certain components in foods.
Soy allergy is triggered by soy proteins — glycinin and conglycinin — found in most soy products (7).
Even though soybeans are one of the most common allergenic foods, soy allergy is relatively uncommon in both children and adults (61, 62).
SUMMARYIn some people, soy products may suppress thyroid function, cause flatulence and diarrhea, and lead to allergic reactions.
The bottom line
Soybeans are high in protein and a decent source of both carbs and fat.
They are a rich source of various vitamins, minerals, and beneficial plant compounds, such as isoflavones.
For this reason, regular soybean intake may alleviate the symptoms of menopause and reduce your risk of prostate and breast cancer.
However, they can cause digestive problems and suppress thyroid function in predisposed individuals.