A history of modern research into fasting, starvation, and inanition

Abstract

Fasting and starvation (prolonged fasting), are the most severe forms of malnutrition, and are experienced by aquatic and terrestrial species due to physiological, nutritional, or behavioral constraints. Migration, metamorphosis, reproduction, and molting are among the main endogenous factors, while food paucity, unpredictable feeding times, remote feeding grounds, and environmental and climatic changes are other external but similarly decisive cues. When the critical starving period is over, it can necessitate gradual refeeding, induce nutritional shifts, and also induce permanent damage. It has, therefore, always been a goal in physiology to understand the different adjustments during food deprivation and refeeding phases. In this field, most of the studies focusing on the physiological consequences of the imbalance between energy intake and energy expenditure have considered time to be the main function. However, since the late 1970s/early 1980s and the "rediscovery" of earlier studies, some researchers have considered starvation to be a continuous series of different metabolic phases composed of a short initial period of adaptation followed by a second phase characterized by fat oxidation. At this point, body lipid stores are not fully exhausted and a third nonpathological and reversible phase follows during which energy requirements are mostly derived from increased protein utilization. If prolonged, this phase can lead to a critical lethal endpoint, even if food becomes available. More recent studies have investigated the alarm signal that triggers behavioral changes such as nest abandonment and refeeding, and have also examined complex hormonal and metabolic regulations in response to food deprivation, such as the marked reduction of apolipoprotein A-IV levels observed in rodents during long-term fasting. The new challenges in this field concern the severely disrupted populations faced with increasing food restrictions due to anthropization.