Gut microbiota diversity refers to the variety of different microorganisms, including bacteria, viruses, fungi, and other microbes, present in the gastrointestinal tract. A diverse gut microbiota typically includes a wide range of microbial species, which is associated with better overall health.

The gut lumen is the hollow interior space inside the gastrointestinal tract (GIT), starting from the mouth and extending to the anus. It is the region of the GI tract where ingested food and liquids are mixed with digestive secretions and undergo chemical and mechanical digestion. The gut lumen is surrounded by the other parts of the intestinal wall: the mucosa, the submucosa, the muscularis, and the serosa. It is also home to diverse microbial species known as gut microbiota.

Gut peptides are small protein-like molecules released by the gut and are structurally composed of 36 amino acids. Gut peptides exert biological effects on various organs, including the brain and the gut. Examples include PYY, CCK, and GLP (Holzer et al., 2012).

Gut-associated lymphoid tissues are the gut’s largest mass of lymphoid tissues and immune cells (such as B and T-cells, neutrophils, mast cells, macrophages, and dendritic cells). GALT is critical in maintaining gut health and protecting it from potentially harmful pathogens (Ruth & Field, 2013

Habit is learned behavior acquired through repetition, characterized by automatic and routine actions. These behaviors become ingrained in daily life, shaping individuals’ routines and responses to specific cues or contexts.

Habit formation is the process by which behaviors become automatic through consistent repetition. It involves establishing a routine or pattern that, over time, becomes ingrained in one’s daily life.

The habit loop is a psychological concept that describes the cyclical process through which individuals form and reinforce habits. It consists of three main components: cue (the trigger), routine (the actual behavior), and reward (the outcome).

Eating that occurs automatically and routinely, often triggered by environmental cues rather than hunger, and carried out with little conscious thought.

Habitual intake refers to the regular and continuous intake of a food or substance instead of occasional intake. ‘Occasional’ intake is defined as having dessert 1-3 times per week, for example (as opposed to almost every day).

The health halo effect occurs when consumers perceive a product as healthy based on one or a few positive attributes (e.g., “low fat” or “high fiber”) despite the product containing other less healthy components. This effect can lead to overestimating the product’s overall healthiness, affecting purchasing and consumption habits.