The Biochemistry, Chemistry and Physiology of the Isoflavones in Soybeans and their Food Products

Abstract

In this review of the chemistry, absorption, metabolism, and mechanisms of action of plant isoflavones, emphasis is placed on the isoflavones in soy and the food products derived from them. Soybeans have been part of food history in Asia for several millennia but did not reach the Americas and Europe until the eighteenth century. In the twentieth century, there was a tremendous increase in the cultivation of soybeans in the United States and more recently in South America. Soy foods have entered the U.S. food supply in ever-increasing amounts both in the form of traditional products (soy milk, tofu) and in more subtle ways in dairy and bread= cake products. The isoflavones in non-fermented foods are for the most part in the form of glycoside conjugates. These undergo changes due to different processing procedures. Isoflavones and their metabolites are well absorbed and undergo an enterohepatic circulation. They are often termed phytoestrogens because they bind to the estrogen receptors although weakly compared to physiologic estrogens. This estrogenicity is not the only mechanism by which isoflavones may have bioactivity-they inhibit tyrosine kinases, have antioxidant activity, bind to and activate peroxisome proliferator regulators a and g, inhibit enzymes in steroid biosynthesis, strongly influence natural killer cell function and the activation of specific T-cell subsets, and inhibit metastasis. These various properties may explain the much lower incidence of hormonally-dependent breast cancer in Asian populations compared to Americans and Europeans.

Flavonoids through the eyes of a pharmacologist. Features and problems of pharmacokinetics

“…Этот процесс протекает быстро, так что через 20-30 минут обра-зовавшиеся конъюгаты определяются в серозном (васкулярном) слое кишки и в системном кровото-ке. Кроме того, столь быстрая конъюгация созда-ет достаточно высокий градиент, способствующий пассивному проникновению агликонов из просвета кишечника после гидролиза, обеспечиваемого лак-таза-флоризин-гидролазой [4,5,11,13,28,57]. Конъюгированные флавоноиды в виде анионных дериватов (метилированные и неметилированные глюкурониды и сульфаты флавоноидов) из клеток тонкого кишечника через базолатеральную мем-брану попадают в кровоток системы портальной вены.…”

Phytochemicals in Soy and Their Health Effects

“…Isoflavones can bind to both and isoforms of esterogen receptor (ER), but their binding affinity to ER is about 20 times higher than that to ER (11). However, compared to physiological estrogen such as 17 -estradiol, isoflavones have approximately 100 times weaker affinities (32). Estrogen-like effects have been proposed as one of the major mechanism of action of isoflavone related to their health effects (8).…”

“…For instance, genistein and other isoflavones were found to interact with the peroxisome proliferator activated receptors, PPAR / . These nuclear receptors are activated by fatty acids (PPAR ) and prostaglandins (PPAR ) and serve as transcription factors (32). As polyphenols, isoflavones also have antioxidant activities, which were proposed as another important mechanism of action of isoflavones.…”

“…However, isoflavones are not strong antioxidant may not be able to scavenge oxidants directly. They therefore are considered as antioxidants because of their effects on gene expression of enzymes that enhance antioxidant defenses (32). In addition to what has been discussed above, several other mechanism have been proposed for the activities of isoflavones, including stimulation/inhibition of enzyme activities involved in steroid synthesis and metabolism, targeting thyroid peroxidase, and inhibiting cancer metastasis (32).…”

“…They therefore are considered as antioxidants because of their effects on gene expression of enzymes that enhance antioxidant defenses (32). In addition to what has been discussed above, several other mechanism have been proposed for the activities of isoflavones, including stimulation/inhibition of enzyme activities involved in steroid synthesis and metabolism, targeting thyroid peroxidase, and inhibiting cancer metastasis (32). Consumption of isoflavones has been suggested to have multiple beneficial effects in a number of chronic diseases and medical conditions, including certain types of cancer (33)(34)(35), heart disease (36-38), bone functions (39)(40)(41)(42) and most recently, prevention of obesity (43,44).…”