Effect of 24 to 48-hour fasting on growth hormone levels in healthy adults: a systematic review

Abstract

Introduction: Growth hormone (GH) plays a key role in metabolic adaptation to fasting by stimulating lipolysis and preserving lean mass. However, there is no consensus on the magnitude of the GH response to short-term fasting in healthy adults. Objective: To systematically review the literature on the effect of 24-48 hour fasting on GH levels in healthy adults. Methods: A search was conducted in PubMed, Google Scholar, and Science Direct (2000-2025). Original studies with healthy adults undergoing 24-48h fasting and measuring GH as an outcome were included. A narrative synthesis was performed due to study heterogeneity. Results: Six studies (n=119 participants) were included. Twenty-four-hour fasting increased GH by 3-5 fold, without IGF-1 elevation (hepatic resistance). Prolonged fasting (≥36h) intensified the response, increasing GH pulse frequency and amplitude. The GH increase was associated with decreased insulin and leptin, stimulating lipolysis. Individuals with low basal GH showed greater relative increases. Discussion: Twenty-four to forty-eight-hour fasting significantly increases GH secretion in healthy adults, with a more pronounced response during prolonged fasting and in individuals with low basal GH. The GH-IGF-1 dissociation suggests adaptive hepatic resistance.