The large intestine, also known as the large bowel, is the last part of the GIT and the digestive system, consisting of the cecum, colon, rectum, and anal canal (Washabau & Day, 2013). Unlike the small intestine, it is shorter but has a significantly larger lumen.

A leaky brain is defined as a dysfunction of the blood-brain barrier permeability in which tight junctions become loose or broken, allowing harmful substances to “leak in” into the brain, causing inflammation and detrimental consequences (Obrenovich, 2018).

Leaky gut, also known as increased intestinal permeability, is an adverse digestive condition in which the gut barrier becomes more permeable, allowing the entry of luminal content (microbes, toxins, antigens, undigested food particles) to leak through the gut wall into the bloodstream. This condition is linked to various health problems, including GI problems, brain disorders, autoimmune diseases, allergies or food sensitivities, etc. (Graziani et al., 2019).

The acquisition of novel information, behaviors, or abilities after practice, observation, or other experiences, as evidenced by a change in behavior, knowledge, or brain function. Learning involves consciously or unconsciously attending to relevant aspects of incoming information, mentally organizing the information into a coherent cognitive representation, and integrating it with relevant existing knowledge activated from long-term memory (APA Dictionary of Psychology)

Leptin, also known as the “satiety hormone”, ” is a circulating hormone secreted primarily by adipocytes (i.e., fat cells) to signal nutritional status in direct proportion to fat stores; as fat stores deplete, leptin levels fall, resulting in increased appetite and decreased energy expenditure to replenish fat stores (Pan & Myers, 2018). Leptin regulates energy homeostasis, neuroendocrine function, and metabolism (Münzberg & Morrison, 2015).

Ligands are small signaling molecules that are highly specific and only bind to their respective receptors to initiate particular responses. Ligands could be small proteins, hormones, neuropeptides, neurotransmitters, or even structural components of bacteria such as LPS.

The limbic system is composed of four main brain structures: the hypothalamus, the amygdala, the thalamus, and the hippocampus. It helps regulate behavioral and emotional responses, especially survival-related responses, such as eating behavior. The limbic system and the prefrontal cortex have a reciprocal relationship. The automatic and primitive reactions mediated by the limbic system depend highly on the emotion, reasoning, and decision-making functions mediated by the prefrontal cortex and vice versa.

Lipopolysaccharides (LPS), also called endotoxins, are large molecules composed of lipids (fat) and polysaccharides (sugar) found on the outer walls of gram-negative bacteria. They are potentially toxic and have been implicated in many diseases or infections.

Action where gut peptides influence nearby target cells’ function by binding on their receptors. For instance, short-chain fatty acids (SCFAs) nourish intestinal cells and strengthen intestinal barrier integrity.

Low-density lipoprotein (LDL) cholesterol can build up in arteries, leading to plaque formation and an increased risk of heart disease. It is often referred to as “bad cholesterol.”