# Dietary Soy Impact on Host Transcriptome Profile--A Review
## 1 Introduction  
Known as a wonder food, wonder crop, or meat without bone, soybean has been a matter of intense debate regarding its diet-induced health effects. Soybean is not only a notoriously rich source of proteins and essential amino acids but also of folate, riboflavin and vitamin K, minerals (calcium, magnesium, iron, copper, manganese, molybdenum), and fibers [1, 2]. Replacing meat with soy has beneficial health effects such as lowering cholesterol and saturated fat while increasing folate, calcium, magnesium, iron, vitamin K and fiber intake [3]. In addition, soybean contains unique nutrients such as isoflav (ISO), phenolic acids, phytoalexins, phytosterols, and saponins, the roles of which are not yet fully understood [4]. These bioactive compounds may act through synergic or independent mechanisms to confer positive effects on human health [5]. Global soybean consumption varies from one country to another and even within the same country. For example, the average daily intake of soybean in China, Japan or Taiwan is around 36 g [6], while in Europe and the US is only 4 g [7]. There are also significant changes in dietary habits in Asians living in the US, and even in Asians living in urban vs. rural areas [6]. Furthermore, soy consumption varies according to age. In Japan, as the diet of young adults becomes more and more westernized, soy foods have begun to be replaced, such that older Japanese consume almost twice as much soy as the young ones [8]. These outstanding variations in diet habits might explain the divergent results of the health benefits analyses. Most of the beneficial health effects of a soy diet have been attributed to isoflav, generally known as phytoestrogens [9], while data on other soy phytochemicals are more limited [10]. After being metabolized by gut microbiota, their active compounds, genistein and daidzein, are either absorbed in the small intestine or delivered into the large intestine for further metabolism via intestinal microflora [11]. It is well known that among day-to-day dietary products, only soybean provides a relevant amount of isoflav: 3.5 mg per gram of protein [12]. The concentration of isoflaves highly depends on the processing method: whole soy products such as edamame or soy flour have the highest dose ofisoflavones, while soy milk, soy sauce or other highly processed soy foods have up to 80% lower content of isoflavenes [13]. The cardiovascular benefits of the soy diet are mainly linked to HDL cholesterol elevation and lowering LDL cholesterol/total cholesterol/triglycerides [14; 15]. This effect is directly linked to soy proteins and saponins, which, due to their amphiphilic nature, form insoluble complexes that reduce the absorption of LDL cholesterol in the intestine [16; 17]. Furthermore, the ISO, as well as genistein and daidzein, has an antioxidant effect by lowering LDL cholesterol oxidation [18], stimulating the production of superoxide dismutase [19], activating the Nrf pathway [20], and inhibiting nitric oxide synthesis in macrophages [21; 22; 23]. Of note, the combination of active soy principles was found to have an additive hypocholesterolem effect compared to soy protein ingestion alone [24]. Furthermore, a high intake soy has been shown to promote vascular dilation in the periphery, while the data on cerebrovascular area are not conclusive [25]. However, a possible connection between soy diet and the development and management of vascular cerebral lesions including cerebral cavern malformations (possibly mediated by gut lining bacteria) has not been explored so far [26; 27]. Although supported by many ex vivo and in vivo data, the cancer prevention benefit of a soy enriched diet is still one of the most controversial, mainly due to the modest, inconsistent, and sometimes even controversial epidemiological data [28]. It is unanimously accepted that soy isoflav, in general, and genistein, in particular, are the main cancer-preventing compounds.