# The Role of Fermented Vegetables as a Sustainable and Health-Promoting Nutritional Resource
## 5 Influence of Vegetable-Fermented Foods on Mental Health  
There is a growing body of knowledge suggesting that the GM is a critical mediator that responds to external signals and triggers endogenous functions in the organism. The microbiome-gut-brain (MGB) axis consists of a bidirectional communication network between the GM and the CNS [312]. The GM is influenced by different factors, such as diet [13; 313], age [314; 315], medication use [316], sex [315], ethnicity, and geographical location [317; 318]. The GM and its metabolites influence several host functions, including intestinal [319], immunological [320], and neural components [13; 321] of the MGB axis. Several studies have related mental health and dietary patterns, highlighting the resulting potential influence of dietary intervention strategies on the cognitive well-being of individuals [322; 323]. Consequently, interest is growing in the use of the diet to target the microbiota to promote mental health benefits for the host [324]. Recent research has explored fermented foods as a promising approach for microbiota-targeted interventions, since they serve as vehicles for delivering beneficial microbes and compounds, and they can be utilized therapeutically across several socioeconomic groups due to their potential affordability and accessibility across cultures [325]. Figure 1: Effects of the daily intake of fermented vegetables regarding nutritional components (according to [PERSON] et al. [191]). SFA: saturated fatty acid; SCFA: short-chain fatty acid. Blue arrows: increase in daily intake of particular nutritional components from fermented vegetables compared to fresh ones. Red arrows: decrease in daily intake of particular nutritional components from fermented vegetables compared to fresh ones. The MGB axis enables a continuous bidirectional exchange of information between the gut and the brain through the enteric nervous system. This communication pathway involves a dynamic interaction among diverse elements of the intestinal environment, including cytokines, microbial communities, microbial metabolites, peripheral immune cells, and gut-associated lymphoid tissue. These components relay signals to the brain and vice versa, utilizing the sympathetic and parasympathetic nervous system, neurotransmitters, and the circulatory immune system [326]. In addition to microorganisms and their metabolites, fermented foods are rich in phytochemicals, which can take the form of neurotransmitters, neuroactive substances, and neuromodulators [327], and thus activate the pathways associated with the MGB axis: the circulatory, immune, neuroendocrine, and enteric nervous systems. During digestion, they can lead to the generation of microbial metabolites that may influence the permeability of both the intestinal barrier [328] and the blood-brain barrier (BBB) [329] (Figure 2). Microbial gut dysbiosis is an imbalance in the GM characterized by a decrease in beneficial microorganisms, the development of pathologists, and the alteration of both alpha- and beta-diversity. This state may lead to the development of several mental disorders, such as anxiety, depression, stress, and cognitive or behavioral disturbances [240]. These psychological disorders can be modulated by consuming fermented vegetable foods that contain active probiotics which produce SCFAs and neurotransmitters, mitigating gastrointestinal inflammation, reducing circulating pro-inflammatory cytokines, and improving gut barrier function [330] through systemic circulation [331], or via the vagus nerve [332]. Figure 2 shows the hypothetical roles of the functional components of fermented vegetables in the GM and the brain. Numerous components of fermented foods are currently under investigation for their capacity to influence the immune system. One possible mechanism through which these foods exert their immunomodulatory effects is by activating the hydrocarbonylic acid receptor (HCA3R) resulting from the consumption of foods fermented by LAB.