The GBA-microbiota crosstalk is a bidirectional communication system between the gut, microbiota, and brain. This communication occurs physically or biochemically and interlinks the gut with the cognitive and emotional centers of the brain, thus ensuring adequate mental health and intestinal homeostasis (Mayer, Tillisch, & Gupta, 2015).

Genes are the instruction manuals of living organisms made up of intricate DNA sequences; their function is to direct the production of specific proteins and enzymes required for survival.

The germ-free (GF) animal model refers to the study of animals raised in a sterile environment free of microorganisms (i.e., beneficial and pathogenic microbes) for research purposes (Bhattarai & Kashyap, 2016).

Ghrelin is often referred to as the “hunger hormone.” It is produced by the stomach and stimulates appetite, signaling to the brain that it’s time to eat (Pradhan et al., 2013).

A gland is a group of cells whose function is to produce and secrete a specific substance (such as hormones, digestive juices, tears, saliva, and milk) either directly into the bloodstream (in the case of endocrine glands) or through a duct or other opening inside or outside the body (in the case of exocrine glands) (Maynard & Downes, 2019).

Glucagon-like peptide -1 is a hormone the gut cells produces in response to food intake. GLP-1 reduces food intake and increases insulin secretion (Gribble & Reimann, 2016).

Glycans are sugar molecules with proteins and lipids in their chemical structure.

The Glycemic Index (GI) is a scale that measures how quickly a carbohydrate-containing food raises blood glucose levels compared to a reference food, reflecting its impact on post-meal blood sugar response.

Glycoproteins are molecules composed of carbohydrates and proteins. Mucin, for example, is a type of glycoprotein that gives the mucus layer a gel-like consistency.

The term “gnotobiotic” refers to the study of organisms inoculated in a carefully controlled environment containing one or a few types of organisms to observe their influence on the body or brain (Williams, 2014). For example, germ-free (GF) animals become gnotobiotic after being inoculated with one or more specific bacterial strains. This method assists researchers in studying the interactions between microbes and hosts.