In the last article, we introduced what’s soy isoflavones? Today we will continue the knowledge of soy isoflavones and follow me to find how it benefits the body. As we know, Soybean Isoflavone (SI) is a kind of polyphenol compound in soybeans. Soybean Isoflavone is a natural active substance with estrogen-like effect and similar structure toestrogen, so it is also called phy-toestrogen. Is a kind of non – sterol substance with a wide range of nutritional value and health protection. The resources of soybean isoflavones are very limited in nature and only exist in a few plants of the legume sphenoid subfamily. Soybean is the only meaningful food resource in nutrition. The research status and development prospects of soybean isoflavones were discussed in this paper.
Chemical composition of soy isoflavones
Soybean isoflavone is a kind of secondary metabolites formed during soybean growth. In 1931, soybean isoflavone — genistein was extracted from soybean for the first time, and then two other soybean isoflavones — Daidzein and glycintein were discovered.
Metabolism and absorption
Soybean isoflavones are usually solid, with melting point above 100℃. At room temperature, they are stable, yellow-white, powdery, non-toxic and slightly bitter. It has certain solubility in alcohol, ester and ketone solvents, insoluble in cold water, easily soluble in hot water, difficult to dissolve in petroleum ether, hexane and so on.
Soybean isoflavones are mainly metabolized and absorbed in the human intestine. Setchell et al. first studied the pharmacokinetics of soybean isoflavones in the human body and evaluated the bioavailability of daidzein, daidzein, genistein and genistein in human body. After the intake of isoflavones, the free form of isoflavone aglycogen is released under the action of intestinal bacteria and is absorbed by the body at the upper part of the small intestine or converted into metabolites with higher activity than estrogen, such as equol. Human experiments show that the absorption rate of soybean isoflavone is about 10% ~ 40%. Most of the absorbed isoflavones bind with glucuronic acid, and a small amount of them bind with sulfuric acid. The conjugated products bind under the action of conjugated enzymes produced by colon microorganisms to produce proaglycoside, which is then absorbed into the blood. Most of the rest will be degraded and metabolized by microorganisms in the intestinal lumen through heterocyclic cleavage and eventually excreted in the urine.
Physiological function of soybean isoflavone
Studies have shown that soybean isoflavones have many physiological effects, and the anti-estrogen effect is only one of them. Soy isoflavones and menopause Syndrome Back in the 1940s, researchers noticed that sheep in an Australian pasture had high fertility and found that formononetin, which is rich in a particular clover plant, could be digested into a soy isoflavone, daidzein, in the sheep’s stomach. Further studies have found that soybean isoflavones are similar to mammalian estrogen in structure and have estrogen-like activity (about 10-4-10-3 of 17 hydroxyβ estradiol), so they are called phytoestrogens and are considered as natural substitutes for estrogen.
Australian scientists found that menopausal women who ate 45g of soy a day were 40% less likely to experience menopause. The structure of soybean isoflavones is similar to estradiol, which can bind estrogen receptors with low affinity and have an estrogen-like effect. The estrogen-like effects of soybean isoflavones in vivo show a bidirectional balance regulation function: On the one hand, in a high estrogen environment (e.g., premenopausal women) soybean isoflavones show an anti-estrogen role, when combined with estrogen receptor, more active estrogen in the body can’t combine with the hormonal effect, can avoid the excessive estrogen effects on cells, to reduce harm developing breast cancer tumors associated with estrogen have a certain effect; On the other hand, in a low estrogen environment (such as in postmenopausal women) shows to estrogen, and osteogenesis of estrogen receptors in cells, strengthen the activity of bone cells, promote the produce and secrete of bone matrix and bone mineralization process, can control such as osteoporosis, menopausal syndrome and other diseases associated with estrogen levels decline. There is a lot of experimental evidence that soy isoflavones as phytoestrogens can play an important role in hormone replacement therapy, but some scholars have reservations
Soy isoflavones and breast cancer
Recent studies have also shown that it may act as a natural antioxidant, and many natural antioxidants have anti-tumor properties. In vitro culture of cancer cells confirmed that soy isoflavones have inhibitory effects on the growth and proliferation of breast cancer, gastric cancer, liver cancer, leukemia and other cancer cells. There are many reports on anti-tumor effects of soybean isoflavones in animal experiments at home and abroad. The results show that feeding animals with soybean can reduce the incidence of tumors, prolong the incubation period and reduce the number of tumors.
At present, the anti-tumor mechanisms of soy isoflavones include the following aspects :(1) estrogen-like and anti-hormone effects; (2) antioxidant effect; (3) Regulate cell cycle and induce apoptosis; (4) inhibit the activity of tyrosine kinase; (5) inhibition of topoisomerase activity; (6) Inhibit the formation of tumor angiogenesis.
Soy isoflavones and osteoporosis
It has been reported that soybean isoflavone can prevent postmenopausal osteoporosis as estrogen substitute. The results showed that the excretion of urine isoflavone was higher in the group with high BMD, and the excretion of urine isoflavone was positively correlated with the intake of soybean isoflavone, indicating that the intake of soybean isoflavone had a certain relationship with BMD.
Many animal experiments have confirmed the preventive effect of soy isoflavones on osteoporosis. It was found that supplementation of soybean isoflavones in ovariectomized osteoporosis model rats can increase the bone density of femur and improve the biomechanical properties of bone. It is suggested that genistein and HRT play the same biological role in preventing bone loss. Further study found that there were no significant differences in routine biochemical, liver function and hematology indexes among the three groups. Multiple large doses of a single pure dose of genistein in healthy postmenopausal women do not result in accumulation and have minimal clinical toxicity.
Soy isoflavones and atherosclerosis
Epidemiological data show that the prevalence of cardiovascular disease in the eastern population whose staple food is soybean is significantly lower than that in the western population. Dietary surveys conducted at the same time found that Japanese consumption of soy isoflavones was much higher than in western countries. This suggests that soy isoflavones may have a preventive effect on cardiovascular disease.
The results showed that soybean isoflavone could partially reverse the decrease of SOD activity in red blood cells and liver and the increase of MDA level in the liver of hypercholesterolemia rats. At present, the mature mechanisms are mainly as follows :(1) soy isoflavones can positively regulate LDL receptors, thus promoting cholesterol clearance; (2) To prevent excessive oxidation of LDL, genistein has a significant scavenging effect on lipid free radicals in the lipid peroxidation system; (3) Inhibit the proliferation of vascular smooth muscle cells; (4) Anti-thrombogenesis , genistein can inhibit platelet activation and aggregation by inhibiting tyrosine kinase.
Other physiological functions
Studies have shown that a short-term soy intervention improves memory in both male and female students. Recent studies have found that flavonoids from natural food materials, including quercetin, luteolin, soybean isoflavone, are excellent free radical scavengers and good natural antioxidants. In addition, soybean isoflavone has anti-bacterial, anti-inflammatory and improves immunity.
Soybean isoflavones have important biological activities and have definite effects on estrogenoid, anti-tumor, prevention of osteoporosis and cardiovascular diseases. However, the effects of soybean isoflavones need to be confirmed by human experiments, and its mechanism still needs to be further studied. The research on soybean isoflavone shows that soybean food has an important effect on the health of consumers.
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