Soybeans are among the best sources of plant-based protein. The protein content of soybeans is 36–56% of the dry weight.
One cup (172 grams) of boiled soybeans boasts 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.
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.
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.
This low GI makes soybeans suitable for people with diabetes.
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.
Alpha-galactosides belong to a class of fibers called FODMAPs, which may exacerbate the symptoms of irritable bowel syndrome (IBS).
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.
Vitamins and minerals
Soybeans are a good source of various vitamins and minerals, including:
- 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. Also known as vitamin B9, folate has various functions in your body and is considered particularly important during pregnancy.
- Copper. Dietary intake of copper is often low in Western populations. 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 due to their high phytic acid content.
- 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.
Other plant compounds
Soybeans are rich in various bioactive plant compounds, including:
- 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.
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%).
Health benefits of soybeans
May reduce cancer risk
Eating soy products is linked to increased breast tissue in women, hypothetically increasing the risk of breast cancer. However, most observational studies indicate that consumption of soy products may reduce breast cancer risk.
Studies also indicate a protective effect against prostate cancer in men.
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.
Studies indicate that isoflavones, a family of phytoestrogens found in soybeans, may alleviate these symptoms.
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.