‘Cross-talk’ refers to the bi-directional communication between the gut, its microbiome, and the brain through intricate neuro-immuno-endocrine communication pathways. MGBA cross-talk facilitates many functions, such as digestion, stress regulation, immune system modulation, and cognitive processes.

Microbial diversity measures the variety of species in the gut microbiota. Higher diversity indicates a healthy microbiota because it contains a diverse range of species, each performing a different beneficial function for the host.

Microbial-derived-neurotransmitter synthesis is a process in which gut microbiota and its metabolites stimulate the synthesis and release of neurotransmitters from gut cells.

The terms “micro” and “biome” are derived from Ancient Greek, where “micro” means small and “biome” means life (Berg et al., 2020). The microbiome refers to microorganisms, their genes, and the surrounding environmental conditions (e.g., pH, oxygen and substrate availability, and moisture level) (Marchesi & Ravel, 2015). Module 2 of NP 120 Part I introduces the microbiome in great detail.

Microbiota refers to all of the microorganisms (e.g., bacteria, viruses, and fungi) found in a specific environment, and its diversity (i.e., variety) differs from person to person (Ursell et al., 2012; Marchesi & Ravel, 2015). In this course, we will focus on the microbiota (primarily bacteria) that live in the large intestine of the GIT.

The microbiota-gut-brain axis (MGBA) is a network of interconnected biological systems that facilitates bidirectional communication between the GIT and the brain (Morais et al., 2020). MGBA is essential for maintaining gastrointestinal and microbial ecosystem homeostasis and causing physiological changes in the brain that influence mood and behavior (Morais et al., 2020; Generoso et al., 2021),.

The network of interconnected biological systems within the body that facilitate the bidirectional communication between the gastrointestinal tract and the brain influences all elements of the Diet-mental health relationship (DMHR) within nutritional psychology, including the psychological, behavioral, cognitive, interoceptive, sensory-perceptual, and psychosocial elements.

Microbiota-derived metabolites are the byproducts of gut microbiota that act as signaling molecules and are released during the digestion and fermentation of non-absorbable and non-digestible dietary fibers, e.g., SCFAs.

The microbiota-gut-brain axis (MGBA) is a complex bidirectional communication network involving neural, immune, and biochemical pathways connecting the gut microbiota to the brain. It significantly influences our physiological state and mental well-being.

A bidirectional communication network linking the gut microbiota, gastrointestinal system, and central nervous system through neural, endocrine, immune, and metabolic pathways. This axis influences mood, cognition, behavior, and appetite regulation.