Protein is a polymer compound composed of amino acids with a certain skeleton, which is related to life and life activities. It is an important material basis of the organism, which is not only the main material that constitutes various cell protoplasm, but also nuclear protein and its corresponding ribonucleic acid (DNA, RNA) is the main material basis of inheritance. It has many biological functions, such as the catalysis of enzymes, the physiological regulation of hormones, the oxygen and carbon dioxide carried by hemoglobin, and the immune function of the body. (2) Essential amino acids.
The definition of essential amino acids is: amino acids that are necessary for human body but cannot be synthesized by human body and must be absorbed through food chain. There are usually eight kinds: isoleucine, leucine, lysine, methionine (cystine), threonine, tryptophan, valine and phenylalanine (tyrosine). Methionine and cystine, alanine and tyrosine can be transformed into each other from the analysis of human metabolic pathway, so they are calculated as an essential amino acid respectively. In addition, histidine, also known as semi-essential amino acid, can not meet the needs of human body because of its slow synthesis.
(3) Nutritional quality of soybean protein
Soybean protein powder is extracted from high-quality soybeans in protein. Its protein content is 2-2.5 times that of the original soybean, and it contains trace elements such as potassium, sodium, calcium, magnesium, iron, zinc, manganese, selenium and copper. Soybean protein is one of the sources of high-quality protein for human beings.
After separation and extraction, the amino acid content in soybean protein is much higher than the RDA recommended by FAO and WHO for children and adults, and it is a rare high-quality protein. In addition, the digestion and absorption rate of soybean protein is very good in the north, which is one of the highest in protein. From the fairest egg detection standard proposed by FAO/ WHO /FDA-Protein Digestibility Amino Acid Correction Index (PDCAAS), we can know that soybean protein is better than meat protein, fish protein, peanut oat protein and other bean proteins. For dieters with low calorie, replacing part of protein in diet with soybean protein can not only supplement nutrition, keep all biochemical indexes in the body normal, but also reduce blood lipid and cholesterol, and soybean protein can be easily processed into various delicious foods to make dieters eat happily.
1. Eating 47 grams of soy protein can reduce low-density lipoprotein (LDL) cholesterol, total cholesterol and triglyceride in blood, but not high-density lipoprotein (HDL) cholesterol. For people with high cholesterol levels, as long as 25 grams of soy protein a day can play a significant role.
2. Soy protein can prevent urinary calcium loss and help promote bone health. Animal protein is rich in sulfur-containing amino acids, which will accelerate the loss of calcium in urine and lead to calcium imbalance in the body. The content of sulfur-containing amino acids in soybean is low, which causes the least urinary calcium loss among all high-protein foods.
3. The intake of soybean protein can promote renal function. In the animal experiment of kidney disease, it was found that the experimental group who ate soybean protein food had high survival rate and low degree of kidney damage.
4. Soybean protein can be used to regulate the physiological cycle of premenstrual women, which may reduce the incidence of breast cancer. A long-term dietary study confirmed that people who eat a lot of soy foods have a lower risk of breast cancer.
(D) The close relationship between soybean protein and anticancer.
First of all, talk about soybeans (we call them soybeans). Because it is rich in protein, it has always been the main source of protein for vegetarians. At present, more and more attention is paid to the fact that soybean milk can lower cholesterol (the requirements for lowering cholesterol can be marked on the officially approved soybean milk products in the United States), which is beneficial to cancer prevention. With the testimony of statistics and clinical application, from the perspective of nutrition, the correctness of information sources can be more affirmed. Soybean protein is rich in isoflavones (or translated into isoflavones). Isoflavones are hormone-like compounds that can inhibit the growth of tumor cells caused by hormone imbalance, such as prostate cancer and breast cancer. Its principle of action is to replace hormones (such as testosterone and estrogen) feared by prostate cancer and breast cancer cells, so as to achieve the purpose of alleviating and inhibiting the growth of cancer cells. In addition, according to some studies, genistein contained in soybean can inhibit the growth of prostate cancer and breast cancer. Because genistein can inhibit the enzymes that cause cell growth and inhibit the proliferation of abnormal blood vessels (the latter has the same anticancer mechanism as shark cartilage). Another thing related to breast cancer is fiber. Adequate fiber intake helps to excrete excess fat and indirectly reduces the risk of breast cancer caused by excessive fat intake. It happens that soybean is rich in fiber, so it is beneficial to inhibit the occurrence of breast cancer.
(5) Soybean protein can relieve hot flashes in menopause.
According to research, if menopausal women pay attention to supplementing soybean protein in their diet, it will help to relieve hot flashes. The incidence of hot flashes in Japanese menopausal women is less than 20%, while the incidence of hot flashes in American menopausal women is as high as 85%. It is believed that this is related to the large proportion of soybean protein in Japanese women's diet. Japanese women consume about 200 mg of phytoestrogens every day, mainly from soy products.
Recently, a study was conducted in Italy. After 5 1 menopausal women consumed 60 grams of soy protein every day, hot flashes decreased by 45% after 12 weeks, while 53 other women consumed 60 grams of non-soy casein every day, and hot flashes only decreased by 30% after 12 weeks.
(6) Soybean protein can inhibit hormone secretion related to breast cancer.
According to Reuters new york Health News, the antioxidant compounds contained in beans can reduce the hormone levels related to breast cancer in women. The results of a recent small-scale study show that other factors related to beans also have the effect of reducing the occurrence of tumors.
The researchers found that nine healthy premenopausal women ate soy milk every day, but most antioxidant compounds and isoflavones had been removed. Compared with before removing these substances, the amount of estrogen and luteinizing hormone produced by women after eating is obviously reduced. Other reproductive hormones are not affected, because other sex hormones are also low in animal protein and high in fiber food.
According to the research results published in the Journal of Clinical Endocrinology and Metabolic Diseases, the level of estrogen decreases with the increase of protein and fiber intake of beans. But Dr. Lee-Jane W.Lu, who is in charge of the study, stressed that it is not clear which compound in the diet causes the change of hormone levels. She told Reuters: "The main finding of this study is that it is not difficult to reduce the estrogen level of women. It can be reduced by replacing the energy intake of beans. " Estrogen can stimulate the growth of some kinds of breast cancer cells and play a very important role in the development of some breast cancer cases. Women with a high history of estrogen exposure, such as early menarche, childless or breast-feeding, have a higher risk of breast cancer. Luteinizing hormone can also increase the incidence of breast cancer and promote the growth of tumor cells. Lu and others think: "Our findings have important clinical significance for the prevention of breast cancer, which can be achieved by adjusting the intake of beans."
In this study, the researchers measured the levels of estrogen, luteinizing hormone, sex hormone binding globulin, luteinizing hormone (LH) and follicle stimulating hormone (FSH) in women before eating. Luteinizing hormone and follicle stimulating hormone can stimulate ovarian function. The women in this study added 36 ounces of soy milk to their monthly diet, which contained less than 5 milligrams of isoflavones. Compared with the general diet, the diet in the study contains more carbohydrates and less protein.
(7) Soybean protein can reduce the risk of heart disease.
In the comparative experiment of soybean and animal protein, it is found that the increase of soybean protein can reduce blood cholesterol, which is a "dynamic selection" for people. When there is no drug treatment, soy protein can reduce the harm of coronary heart disease. The research results of Dr. Susan M.Potter, Department of Nutrition Science, International protein Institute of Technology, were recently published in American Soybean Food edited by Indiana Soybean Committee. Fortunately, it was also found that soy protein and different kinds of brass (natural nutrients of soybeans) can improve the function of blood vessels and avoid thrombosis. Dr. Porter's thesis focuses on the role of soybean protein, demonstrating that soybean protein can reduce the content of low-density lipoprotein (low-density lipoprotein cholesterol) while maintaining or increasing the content of high-density lipoprotein (HDL cholesterol). LDL can usually be called "bad cholesterol", while HDL is "good cholesterol". Studies have shown that soybean protein can resist and reduce blood lipid. Fortunately, the paper writes that a different kind of brass (genistein) can improve the activity of blood vessels and simulate the damage of blood vessels with the formation of thrombosis.