Adaptive Effects of Endocrine Hormones on Metabolism of Macronutrients during Fasting and Starvation: A Scoping Review

Abstract

Food deprivation can occur for different reasons. Fasting (<24 h duration) occurs to meet religious or well-being goals. Starvation (>1-day duration) occurs when there is intentional (hunger strike or treatment of a medical condition) or unintentional (anorexia nervosa, drought, epidemic famine, war, or natural disaster) food deprivation. A scoping review was undertaken using the PubMed database to explore 1805 abstracts and review 88 eligible full-text articles to explore the adaptive relationships that emerge between cortisol, insulin, glucagon, and thyroid hormones on the metabolic pathways of macronutrients in humans during fasting and starvation. The collected data indicate that fasting and starvation prime the human body to increase cortisol levels and decrease the insulin/glucagon ratio and triiodothyronine (T₃) levels. During fasting, increased levels of cortisol and a decreased insulin/glucagon ratio enhance glycogenolysis and reduce the peripheral uptake of glucose and glycogenesis, whereas decreased T₃ levels potentially reduce glycogenolysis. During starvation, increased levels of cortisol and a decreased insulin/glucagon ratio enhance lipolysis, proteolysis, fatty acid and amino acid oxidation, ketogenesis, and ureagenesis, and decreased T₃ levels reduce thermogenesis. We present a potential crosstalk between T₃ and the above hormones, including between T₃ and leptin, to extend their adaptive roles in the metabolism of endogenous macronutrients during food deprivation.

Keywords: cortisol; fasting; glucagon; insulin; macronutrients; metabolism; starvation; thyroid hormones.

Figure 1

Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flow diagram used to indicate the number of reports that were searched and identified from the PubMed database for the scoping review process [42].

Figure 2

Effects of endocrine hormones on metabolism of endogenous macronutrients during fasting (<24 h) and starvation (>1 day). TRH: thyrotropin-releasing hormone; T₃: triiodothyronine; rT₃: reverse T₃; TSH: thyroid-stimulating hormone; upward arrow (↑) indicates “increase” and downward arrow (↓) indicates “reduction” for a metabolic reaction during the indicated food deprivation. The data presented in this figure are extracted from eligible full-texts and also from other records through reference checking of the eligible full-texts.