Soy products are considered a suitable alternative to animal foods. This is due not only to the high content of high-quality protein but also to the more favorable fat composition. Unlike food of animal origin, soy foods do not contain neither cholesterol nor high levels of saturated MK. Instead they have enough fiber and polyunsaturated fatty acids. Soybeans contain at least carbohydrates of all legumes, but like others they also contain indigestible oligosaccharides that can cause gas.
Soybeans are rich in high contents of potassium, phosphorous, calcium, magnesium and sodium; furthermore, other trace minerals are also found, for instance, iron, zinc, manganese, cooper and selenium, nickel and chromium. Generally mineral bioavailability in foods of plant origin is lower than of food of animal origin. The reason is a presence of antinutrients, especially phytic acid, which reduces the usability of nutrients. Suitable method of preparing soybeans such as germination, soaking or fermentation can reduce the amount of antinutrients.
Soy milk is a great alternative to cow’s milk for people suffering from lactose intolerance because they are lactose sugar-free. However, their main problem is the low content and usability of calcium. Calcium is essential for maintaining the bone mass, teeth and muscles activity. Soy milk contains 200 mg of calcium per liter, but cow’s milk 1200 mg. Therefore, milk and dairy products are recommended as their optimal source. Soybeans contain high amount of vitamin E, which helps protect cells from oxidative stress. The vitamin C content is zero, but it can be increased by soaking.
Soybeans contain a moderate amount of substances known as purines, a typical legume ingredient, whose consumption should be reduced in individuals suffering from gout. People with a higher risk of developing calcium-oxalate kidney stones should reduce consumption of soy foods because of high oxalate content. Soybeans also contain goitrogenic substances that cause inadequate synthesis of thyroid hormones, which is reflected in reduced function and visible swelling. Their negative effects can be decreased by heat treatment due to their thermolabile nature.
Soybeans are interesting not only from nutrition viewpoint but also from isoflavones content, whose influence on human health is often subject of discussion. Due to their similar chemical structure and biochemical activity to estrogens (female sex hormones), they are called phytoestrogens. Because of this similarity, isoflavones can be used in the menopause period. During menopause, the ovarian production of estrogens decreases. A reduction of estrogen levels in the blood leads a series of characteristic symptoms of menopause, such as insomnia, excessive sweating, headaches, irritability, depression and hot flashes. Isoflavones alleviate these bad symptoms. During menopause, they also reduce the risk of osteoporosis, positively affect learning, visual memory, and prevent Alzheimer’s disease. According to clinical trials, isoflavones improve vascular endothelium function, arterial stiffness and stretchability, thereby facilitating blood flow, lowering blood triglycerides and LDL cholesterol, and thus protecting against the risk of atherosclerosis. They also have strong antioxidant effects comparable to vitamin E. In premenopausal women, the phytoestrogens act as antiestrogens when the estrogen levels are high. Their potential antiestrogenic benefits are evidenced in hormone-dependent cancers, such as breast cancer.
Common question is “How does isoflavones affect men?” The results of individual studies are often unambiguous but the latest meta-analysis of all studies deals with soy isoflavones has concluded that they do not affect male reproductive system.
Soybeans are also a part of the diet of children, and even the smallest. Soy infant nutrition meets all requirements for infant feeding. Soy based formulas have been used to treat infants with cow’s milk allergy, lactose intolerance or galactosemia. It has been used for several decades. No negative effects of isoflavones have been reported on children’s health yet. However. soybeans are considered to be one of the most common allergenic foods. Soybean allergy is most common among infants and young children who are exposed to soy infant nutrition. The incidence in Europe is around 2%, in adults it is lower because the allergy is disappeared already in childhood.
Concerns with soybeans, especially with the isoflavone effect on human health, are mainly based on the results from animal studies but human research has shown safety. Soy foods have been consumed for centuries in Asian countries. Epidemiologic studies have showed a lower incidence of osteoporosis in populations consuming diets high in soy, such as Asians, when compared to western populations. Many potential benefits have been linked to intake of soy products, for example consumption of soy foods may contribute to lower incidences of coronary heart diseases, atherosclerosis, type 2 diabetes, and decreased risk of certain types of cancer such as breast and prostate cancers as well as better bone health and relief of menopausal symptoms.
Consumption of soy foods can offer health benefits while minimizing the possible harmful effects of the high energy diet of the present.