The body’s aim to maintain a stable internal environment.

Eating in response to a perceived energy need arising from the body’s homeostatic pathways in the brain signal a physiological depletion of energy stores and results in increased motivation to eat (Lutter & Nestler, 2009).

Homeostatic feeding involves the dietary intake of nutrients and calories needed to survive biologically and meet energy needs (i.e., often referred to as ‘maintaining the body’s homeostatic processes’).

The biological processes that maintain energy balance, including hunger and satiety signals, typically governed by hormones such as ghrelin and leptin and brain regions like the hypothalamus.

Food intake is regulated by two complementary pathways in the body and brain that signal us to consume food: the homeostatic and hedonic pathways. The homeostatic pathway controls energy balance by increasing signaling to motivate us to eat following the depletion of energy stores. Hedonic or reward-based regulation can override the homeostatic pathway and enhance signals in craving and consumption of HPFs during periods of relative energy abundance (Lutter & Nestler, 2009).

Hormones are chemical signaling molecules secreted directly into the bloodstream by glands and carried in the circulation to target tissues and organs where they can bind to specific cell sites known as receptors. By binding to receptors, hormones elicit various biological responses in the tissues containing the receptors (Stárka & Dušková, 2020).

Hosts in biology are larger organisms that harbor smaller organisms inside or on their bodies (Casadevall & Pirofski, 2015). In this course, we commonly use this term to refer to animals used in scientific research studies or humans, with the smaller organisms being millions of gut microbes.

The HPA (hypothalamic-pituitary-adrenal) axis dysbiosis-neuroinflammatory cycle is a proposed mechanism of how chronic stress and an imbalanced gut microbiota can contribute to the development and perpetuation of neuroinflammation and mental disorders.

Hunger is a psychological state characterized by a desire to eat (Stevenson, 2024). It strongly motivates an individual to seek out and consume food. Initially, researchers believed that it occurs when blood sugar levels drop and the stomach signals the brain to seek nourishment. More recently, feelings of hunger have been linked to an interplay between levels of various hormones, most notably ghrelin.

Stevenson, R. J. (2024). The psychological basis of hunger and its dysfunctions. Nutrition Reviews, 82(10), 1444–1454. https://doi.org/10.1093/nutrit/nuad092

Hunger hormones stimulate appetite and the desire to eat. Ghrelin is a notable example of a hunger hormone.