Abstract
Typically, the development of anorexia nervosa (AN) is attributed to psycho-social causes. Several researchers have recently challenged this view and suggested that hypothermia and hyperactivity (HyAc) are central to AN. The following hypothesis will attempt to clarify their role in AN. Anorexia nervosa patients (ANs) have significantly lower core temperatures (Tcore) compared to healthy controls (HCs). This reduced temperature represents a reset Tcore that needs to be maintained. However, ANs cannot maintain this Tcore due primarily to a reduced basal metabolic rate (BMR); BMR usually supplies heat to sustain Tcore. Therefore, to generate the requisite heat, ANs revert to the behavioral-thermoregulatory strategy of HyAc. The majority of ANs (~89%) are reportedly HyAc. Surprisingly, engagement in HyAc is not motivated by a conscious awareness of low Tcore, but rather by the innocuous sensation of “cold- hands” frequently reported by ANs. That is, local hand-thermoreceptors signal the brain to initiate HyAc, which boosts perfusion of the hands and alters the sensation of “cold-discomfort” to one of “comfort.” This “rewarding” consequence encourages repetition/habit formation. Simultaneously, hyperactivity increases the availability of heat to assist with the preservation of Tcore. Additionally, HyAc induces the synthesis of specific brain neuromodulators that suppress food intake and further promote HyAc; this outcome helps preserve low weight and perpetuates this vicious cycle. Based on this hypothesis and supported by rodent research, external heat availability should reduce the compulsion to be HyAc to thermoregulate. A reduction in HyAc should decrease the production of brain neuromodulators that suppress appetite. If verified, hopefully, this hypothesis will assist with the development of novel treatments to aid in the resolution of this intractable condition.
Highlights
In 1868, Gull (1997) published the first medical report on anorexia nervosa (AN)
These factors contribute to the preservation of low weight and the perpetuation of this vicious cycle
This hypothesis will generate research to further explore the role of hypothermia and hyperactivity in AN. ‘‘The success of treatment. . .depends on the correct diagnosis and a sufficient understanding of the factors underlying the symptom constellation of the disease or disorder’’ (Casper, 2018)
Summary
In 1868, Gull (1997) published the first medical report on anorexia nervosa (AN). This publication dealt with the classic symptoms of abnormally low body weight and refusal to eat, predominantly in female patients. It consists of activities such as gesturing, shifting in one’s seat/dynamic sitting (van der Berg et al, 2019), frequently moving from sit-to-stand, fidgeting while sitting or standing, swinging legs or tapping feet while seated, fiddling with a pencil, rubbing hands together, picking at nails, deliberately tensing abdominal or leg muscles, and gum chewing (Crisp, 1967; Kron et al, 1978; Gull, 1997; Belak et al, 2017; Kotz et al, 2017; Dittmer et al, 2018; Casper et al, 2020) These SPA activities would generate metabolic heat, probably to a lesser degree compared to NEAT (van der Berg et al, 2019). If this proves to be the case, ‘‘heating’’ the AN during refeeding may be highly advantageous
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