A process that starts in the nose with the stimulation of olfactory sensory neurons and terminates in higher cerebral centers which, when activated, make us consciously aware of an odor (Slotnick, 2009).

Oligosaccharides are carbohydrates comprised of 3 to 7 saccharide (or sugar) units. For instance, lactose (“milk sugar”) is an oligosaccharide in breast milk and baby formula. In addition, oligosaccharides are a valuable food source for various beneficial bacteria residing in the gut.

Opportunistic microbes (bacteria) are typically non-pathogenic microorganisms that act as pathogens in certain circumstances. They lay dormant for long periods until the hosts’ immune system is suppressed, and they seize the opportunity to attack.

The pathway by which oral microbes can be translocated to the gut and vice versa during compromised oral gut integrity. For instance, Fusobacterium nucleatum is an oral-gut translocator and can cause colorectal cancer if present in high abundance.

The orexigenic gut peptides are derived from the Greek word ὄρεξις (órexis,”appetite”). They are primarily produced in the stomach to stimulate appetite and food intake (Sobrino Crespo et al., 2014).

The in-mouth sensory perception of food (Lasschuijt & Mars, 2020).

Ambient odors presented through the nose that have their most important function in the anticipation phase of eating (Boesvelt, 2017).

Orthorexia, though not yet a formally recognized mental health diagnosis, is characterized by an obsessive or pathological preoccupation with “healthy” eating, often involving rigid dietary rules and an extreme focus on food purity. This fixation can lead to significant emotional distress when self-imposed dietary standards are violated, as well as serious medical and psychosocial impairments, including malnutrition and social isolation. While diagnostic criteria remain debated, core features include an intense focus on “clean” eating and its associated health consequences.

Oxidative stress is an imbalance between the production of harmful reactive oxygen species (ROS) and the body’s ability to neutralize them. It can potentially cause cellular damage and contribute to various health conditions.