Fermented soy consumption has been shown to have a number of health benefits, however, the mechanisms through which fermented soy products exert these effects are totally unknown. Here we found that fermented soy beverage Q-CAN® alters the microbiome in lean, and healthy obese individuals, with a number of the changes occurring in a direction expected to improve overall health. In detail, we found that there was no effect on alpha diversity in the microbiome in the stool or saliva. There was alpha diversity however: 1) While taking Q-CAN®, at phylum level, in the stool of lean individuals there was an increase in Actinobacteria, and in obese individuals there was an increase in Fusobacteria (Fig. 2), 2) While taking Q-CAN®, at the family level in the stool of lean individuals, there was an increase in Bifidobacteriacea and EtOH8, and a decrease in S24–7 (Fig. 3), and 3) While taking Q-CAN®, at a genus level in the stool of lean individuals, there was an increase in Blautia, Bifidobacterium and Staphylococcus (Fig. 4).
There is now a large amount of data associating changes in the microbiome with physiological changes with impact on health, but very few studies in humans regarding the effects of soy products . Microbiome diversity is considered to be positive and it was reassuring to see that Q-CAN® did not decrease microbiome diversity in the stool or saliva (Fig. 1b-e). The increase in Actinobacteria in lean individuals taking Q-CAN® (Fig. 2a), is of interest as Actinobacteria are one of the four major phyla of gut microbiota and has a crucial role in maintaining gut homeostasis. Actinobacteria are non-motile, multiple branching rods, gram positive, anaerobic bacteria (families: Bifidobacteria, Propionibac-teria and Corynebacteria) . Within this phylum the increase was found to be in the family Bifidobacteria (Fig. 3a). Bifidobacteria have high production of short chain fatty acids (SCFA), and one of the beneficial effects of this is in the maintenance of gut barrier due to the production of butyrate . Bifidobacteria can protect the host from enteropathogenic infections, such as entero-haemorrhagic Eschericl1ia coli and Shigella, and this thought to be due their high production of acetate and the biotransformation of nutrients in the diet [21,22,23]. This occurs via the fermentation of large polysaccharides, oligosaccarides, unabsorbed sugars and fibers. This results in the release hydrogen, carbon dioxide and SCFAs. It furthermore results in the degradation of proteins, the regulation of lipid metabolism, and the absorption and biosynthesis of vitamin K, iron, calcium and magnesium [24, 25]. Bifidobacteria are also important in the maintenance of a tolerogenic immune environment, and this is thought to be through the stimulation of intrahepatic lymphocytes [26, 27]. This is supported by an increase in gut permeability that leads to the translocation of LPS into the serum when there is a decrease in the number of Bifidobacteria . This provides immune stimulation, and sustains chronic inflammatory conditions, such as insulin resistance, diabetes and liver diseases . In a high fat diet mouse model, administration of Bifidobacterium pseudocatenulatum results in down-regulation of inflammation by reducing the production of inflammatory cytokines and chemokines, especially IL-6 and MCP-1 . Overall Bifidobacteria are seen as improving gut barrier function and reduce the translocation of pro-inflammatory molecules such as lipopolysaccharide into the blood stream . Bifidobacteria and Lactobacilli, are the cornerstone of many probiotic therapeutic approaches. For example a mixture of lyophilized four Lactobacilli and three Bifidobacteria strains has been demonstrated to be effective in several conditions including pouchitis, non-alcoholic steatohepatitis and in the prevention of antibiotic associated diarrhea [31,32,33]. Bifidobacteria treatment has also been demonstrated to improve symptoms of irritable bowel syndrome .
A significant increase in the phylum Actinobacteria and the family Bifidobacteria in the stool was not seen in obese individuals, however there was a trend in that direction (Fig. 2b and 3b). The lack of positive association may be due to the relatively small samples size of ten individuals in each group, and with larger samples sizes a significant increase may be seen. There was a statistically significant increase in the phylum Fusobacteria in the stool of obese individuals but this increase was not followed through at the family (Fusobacteriaceae) level and is of unclear significance. The species Fusobacterium nucleatum has been shown to be associated with colon cancer, although this association has not been universally reproduced [35, 36].
In lean individuals there was also an increase in the family of EtOH8 anaerobic bacteria, (Fig. 3c), but relatively little is known about the biological significance of this and it is difficult to speculate. The uncultured S24–7, a member of the Bacteroidetes family, was reduced in lean individuals while taking Q-CAN® (Fig. 3a). S24–7 are highly anaerobic bacteria that are localized to the gastrointestinal tracts of homeothermic animals and are increasingly being recognized as a numerically predominant member of the gut microbiota but due to the inability to culture them little is known about the nature of their interactions with the host .
At the genus level there was an increase in Blautia (family: Lachnospiraceae, order: Clostridiales, class: Clostridia, and phylum: Firmicutes) (Fig. 4a). Higher levels of Blautia have been associated with several positive health features including nutrient assimilation, immunological health, lower amount of visceral fat, reduced risk of graft versus host disease and [38,39,40], and administration of Blautia has been proposed as a treatment for cancer .
In the saliva of lean individuals there was an increase in family Veillonellaceae (phylum Firmicutes, with three genera Veillonella, Acidaminococcus, and Megasphaera) while on Q-CAN® (Fig. 6a). Members of the family Veillonellaceae are of particular interest for their probiotic effects but to date this has been investigated in animal husbandry with trials showing improvement in energy balance and inhibiting colonization by antibiotic resistance strains of bacteria [42, 43]. If it will be interesting to see if such beneficial effects are also found in the future in humans.
In addition to the phylogenetic analysis above it is important to consider analysis at a functional level by addressing changes in genes with a shared function. An example of this is the consideration of bacterial genes whose products are capable of metabolizing estrogens, identified as the estrobolome [44, 45]. A subgroup of estrogens undergoes a first passage in the liver with glucuronization or sulfunation allowing for excretion in bile, urine and feces. These estrogens can be uncombined by enteric bacterial β-glucuronidase and β-glucosidase, determining their resorption in blood circulation. At present the metabolic functions of a minority of bacterial genes has been identified. As this increases the data set presented here will be increasingly valuable and allow for analysis of Q-CAN® induced changes in the functional capacity of the microbiome.
When comparing the lean and obese populations it is clear that Q-CAN® consumption resulted in a greater number of changes in the lean than the obese (Phylum lean 1: obese 1, family lean 3: obese 0, genus lean 3: obese 0). This may be due to the microbiota of obese individuals having less diversity and therefore less opportunity for Q-CAN® to interact with a range of microbes [46,47,48,49,50,51,52,53].