**2. Nutrition profile of soy**

Soy is a very nutritious plant, and the only complete plant protein. Protein in soy is not only high, but comparable in quality to animal protein regarding amino

**27**

**Figure 2.**

**Figure 1.**

*Similarity of isoflavones to estrogens.*

*Structure of estrogen and isoflavones.*

*Evidence for the Effectiveness of Soy in Aging and Improving Quality of Life*

acid content and digestibility [24]. The carbohydrate content of soybeans is not only low, but poorly digested by intestinal enzymes, and thus behaves as a prebiotic for beneficial bacteria [25]. The fat content is highly variable among different soybean varieties, but includes 10–15% saturated fat, 19–41% monounsaturated fat, and

Most notably, soybeans contain isoflavones. The three main isoflavones present in soybeans include genistein (50% of isoflavones), daidzein (40% isoflavones) and glycitein (10% of isoflavones) [27]. Isoflavones are also classified as phytoestrogens because of their similar structure to estrogen (**Figures 1** and **2**). Isoflavones are more bioactive in their unconjugated (aglycon) form than their conjugated form, which must be hydrolyzed in the intestine to release the aglycons [28]. Additionally, fermented soy has more unconjugated isoflavones, thus making fermented soy foods more pharmacokinetically beneficial [29]. Soy isoflavones are also metabolized by gut bacteria, which leads to many different metabolites, the most biologically active being euqol [30]. Equol is structurally similar to estrogen, but inhibits growth of mammary tumors and may act as a selective estrogen receptor modulator (SERM) [31]. Isoflavones have anti-oxidative and anti-inflammatory properties, as well as the ability to alter gene expression, specifically in estrogen-responsive genes [32]. It is this ability that often leads health practitioners to believe that soy may be dangerous for certain populations, specifically breast cancer, which will be later discussed in this chapter. However, these SERM like capabilities are responsible for

*DOI: http://dx.doi.org/10.5772/intechopen.85664*

46–62% polyunsaturated fat [26].

many of soy's positive effects on health.

*Evidence for the Effectiveness of Soy in Aging and Improving Quality of Life DOI: http://dx.doi.org/10.5772/intechopen.85664*

acid content and digestibility [24]. The carbohydrate content of soybeans is not only low, but poorly digested by intestinal enzymes, and thus behaves as a prebiotic for beneficial bacteria [25]. The fat content is highly variable among different soybean varieties, but includes 10–15% saturated fat, 19–41% monounsaturated fat, and 46–62% polyunsaturated fat [26].

Most notably, soybeans contain isoflavones. The three main isoflavones present in soybeans include genistein (50% of isoflavones), daidzein (40% isoflavones) and glycitein (10% of isoflavones) [27]. Isoflavones are also classified as phytoestrogens because of their similar structure to estrogen (**Figures 1** and **2**). Isoflavones are more bioactive in their unconjugated (aglycon) form than their conjugated form, which must be hydrolyzed in the intestine to release the aglycons [28]. Additionally, fermented soy has more unconjugated isoflavones, thus making fermented soy foods more pharmacokinetically beneficial [29]. Soy isoflavones are also metabolized by gut bacteria, which leads to many different metabolites, the most biologically active being euqol [30]. Equol is structurally similar to estrogen, but inhibits growth of mammary tumors and may act as a selective estrogen receptor modulator (SERM) [31]. Isoflavones have anti-oxidative and anti-inflammatory properties, as well as the ability to alter gene expression, specifically in estrogen-responsive genes [32]. It is this ability that often leads health practitioners to believe that soy may be dangerous for certain populations, specifically breast cancer, which will be later discussed in this chapter. However, these SERM like capabilities are responsible for many of soy's positive effects on health.

**Figure 1.** *Similarity of isoflavones to estrogens.*

**Figure 2.** *Structure of estrogen and isoflavones.*
