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 in Western countries heavily processed soy products are much more common.
Various soy products are available, including soy flour, soy protein, tofu, soy milk, soy sauce, and soybean oil.
Soybeans contain antioxidants and phytonutrients that have been linked with various health benefits, while concerns have also been raised about adverse effects.
Aside from water, soybeans are mainly composed of protein, but they also contain good amounts of carbs and fat.
The table below contains information on all the basic nutrients in soybeans.
Soybeans are among the best sources of plant-based protein.
The protein content of soybeans ranges from 36 to 56% of the dry weight (, , ).
One cup of boiled soybeans (172 g) contains around 29 grams of protein ().
The nutritional value of soy protein is good, although the quality is not quite as high as animal protein ().
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 ().
Consumption of soy protein has been linked with a modest decrease in cholesterol levels (, , ).
Soybeans also contain bioactive proteins, such as lectin and lunasin, which may have anti-cancer properties ().
Bottom Line: Soybeans are a very rich source of plant-based protein, making them ideal for vegan diets.
Soybeans are rich in fat.
In fact, soybeans are classified as oilseeds and are often 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 ().
The predominant type of fat in soybeans is linoleic acid, accounting for approximately 50% of the total fat content.
Bottom Line: As a good source of fat, soybeans are used in the production of soybean oil.
The low glycemic index makes soybeans particularly suitable for people with diabetes.
Soybeans contain a fair amount of both soluble and insoluble fibers.
The insoluble fibers are mainly alpha-galactosides, such as stachyose and raffinose. These fibers may cause flatulence and diarrhea in sensitive individuals (, ).
Alpha-galactosides belong to a class of fibers called FODMAPs, which may exacerbate the symptoms of irritiable bowel syndrome (IBS) ().
Despite unpleasant side effects in some people, soluble fibers in soybeans are generally considered to be healthy.
They are fermented by bacteria in the colon, leading to the formation of short-chain fatty acids, such as butyrate, which may improve colon health and cut the risk of colon cancer (, ).
Bottom Line: Soybeans are low in carbs, but fairly high in fiber. The fiber is good for colon health, but may cause digestive problems in some people.
Soybeans are a good source of various vitamins and minerals.
- Molybdenum: Soybeans are rich in molybdenum, an essential trace element, primarily found in seeds, grains and legumes ().
- Vitamin K1: The form of vitamin K found in legumes is known as phylloquinone. It plays an important role in blood clotting ().
- Folate: One of the B-vitamins, also known as vitamin B9 or folic acid. It has various different functions in the body and is considered to be particularly important during pregnancy ().
- Copper: Dietary intake of copper is often low in Western populations. Copper deficiency may have adverse effects on heart health ().
- Manganese: A trace element found in most foods and drinking water. Manganese is poorly absorbed from soybeans because of their high phytic acid content ().
- Phosphorus: Soybeans are a good source of phosphorus, an essential mineral that is abundant in the Western diet.
- Thiamin: Also known as vitamin B1, thiamin plays an important role in many body functions.
Bottom Line: Soybeans are a good source of several vitamins and minerals, including vitamin K1, folate, copper, manganese, phosphorus, and thiamin.
Soybeans are rich in various bioactive plant compounds.
- Isoflavones: A family of antioxidant polyphenols with a variety of health effects. Often referred to as phytoestrogens ().
- Phytic acid: Found in all plant seeds, phytic acid (phytate) impairs the absorption of minerals, such as zinc and iron. It can be reduced by boiling, sprouting, or fermenting the beans ().
- Saponins: One of the main classes of plant compounds in soybeans (). Soy saponins have been found to reduce cholesterol in animals ().
Bottom Line: Soybeans are a rich source of various bioactive plant compounds. These include isoflavones, saponins, and phytic acid.
Of all the phytonutrients in soybeans, isoflavones are worth mentioning.
Soybeans contain higher amounts of isoflavones than other common foods ().
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%) ().
Some people possess a special type of gut bacteria that are able to convert daidzein to equol, a substance considered to be responsible for many of the beneficial health effects of soybeans.
People who are so-called equol producers are expected to benefit much more from soy consumption than those who are not ().
The percentage of equol producers is higher in Asian populations and among vegetarians than in the general Western population (, ).
Bottom Line: Isoflavones are one of the main plant compounds in soybeans, responsible for many of their health effects.
Like most whole foods, soybeans have a number of beneficial health effects.
Prevention of Breast and Prostate Cancer
Cancer is one of the leading causes of death in modern society.
Eating soy products has been linked with increased breast tissue in women (, , ), hypothetically increasing the risk of breast cancer.
However, most observational studies indicate that consumption of soy products may reduce the risk of breast cancer (, ).
Studies also indicate a protective effect against prostate cancer in men (, , ).
A number of soybean components may be responsible for the potential cancer-preventive effects. These include isoflavones, lectin, and lunasin (, ).
Exposure to isoflavones early in life may be particularly protective against breast cancer later in life (, ).
Keep in mind that all of the human studies on this subject are so-called observational studies. They indicate an association between soy consumption and cancer, but do not prove causation.
Bottom Line: Soybeans contain a number of plant compounds that may help prevent breast and prostate cancer.
Alleviation of Menopausal 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, effects that are brought about by a reduction in estrogen levels.
Interestingly, Asian women, especially Japanese women, are less likely to experience symptoms related to menopause 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 the symptoms of menopause (, ).
Soy products do not affect all women in this way. Soy only seems to be effective in so-called equol producers, women who possess a type of gut bacteria able to convert isoflavones into equol.
Equol has been suggested to be responsible for many of the beneficial health effects of soy consumption.
Daily intake of 135 mg of isoflavones for one week, equivalent to 68 g of soybeans per day, reduced menopausal symptoms only in equol producers ().
Traditionally, hormonal therapies have been used as a treatment for menopausal symptoms. Today, isoflavone supplements are widely used as an alternative treatment ().
Bottom Line: Eating soybeans may help alleviate the symptoms of menopause.
Osteoporosis is a condition characterized by reduced bone density and increased risk of fractures, especially in elderly women.
Consumption of soy products may reduce the risk of osteoporosis in women that have undergone menopause (, ).
These beneficial effects seem to be caused by isoflavones (, , , ).
Bottom Line: Soybeans may cut the risk of osteoporosis in postmenopausal women.
Even though soybeans have a number of health benefits, some individuals need to limit the consumption of soy products, or avoid them altogether.
Suppression of Thyroid Function
There are concerns that high consumption of soy products may suppress thyroid function in some people and contribute to hypothyroidism ().
The thyroid is a large gland that regulates growth and controls the rate at which the body expends energy.
Studies indicate that isoflavones, found in soybeans, may suppress the formation of thyroid hormones in both animals and humans (, ).
One Japanese study in 37 adults reported symptoms related to suppressed thyroid function after eating 30 grams of soybeans every day for 3 months.
The symptoms included discomfort, sleepiness, constipation, and thyroid enlargement, all of which disappeared after the study had ended ().
In another study, isoflavone supplementation (16 mg) every day for 2 months suppressed thyroid function in 10% of adults with mild hypothyroidism.
The amount of isoflavones consumed was rather small, or equivalent to 8 grams of soybeans per day (, ).
However, most studies in healthy adults have not found any significant link between soy consumption and changes in thyroid function (, , ).
A meta-analysis of 14 studies found no significant adverse effects of soybean consumption on thyroid function in healthy adults, whereas infants born with thyroid hormone deficiency (congenital hypothyroidism) were considered at risk ().
In short, regular consumption of soy products or isoflavone supplements may lead to hypothyroidism in sensitive individuals, especially in those with an underactive thyroid gland to begin with.
Bottom Line: Soy products may suppress thyroid function in predisposed individuals.
Flatulence and Diarrhea
Like most other beans, soybeans contain insoluble fibers, mainly raffinose and stachyose, which may cause flatulence and diarrhea in sensitive individuals (, ).
Although not unhealthy, these side effects of soybean consumption can be unpleasant.
Belonging to a class of fibers called FODMAPs, raffinose and stachyose may worsen the symptoms of irritable bowel syndrome (IBS) (), a common digestive disorder.
If you have IBS, avoiding or limiting the consumption of soybeans may be a good idea.
Bottom Line: High consumption of soybeans may cause flatulence and diarrhea in some people.
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 ().
Even though soybeans are one of the top 8 most common allergenic foods, soy allergy is relatively uncommon in both children and adults (, ).
Bottom Line: Some people are allergic to soybeans and need to avoid them altogether.
Soybeans are high in protein, and are also 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, soybeans may reduce the risk of breast and prostate cancer, and alleviate the symptoms of menopause.
On the negative side, they can cause digestive problems and suppress thyroid function in predisposed individuals.