Endocrine response to intermittent fasting: A systematic review of hormonal changes
DOI:
https://doi.org/10.48797/sl.2026.480Keywords:
PosterAbstract
Background: Intermittent fasting encompasses alternating periods of food intake and dietary restriction [1]. This practice has gained prevalence, motivated by cultural, religious, and health objectives [1], yet endocrine adaptations across different protocols remain incompletely characterized [1,2]. The heterogeneity of fasting protocols (short-term, alternate-day, periodic, and time-restricted feeding [2]) contributes to variable endocrine responses [3]. Objective: This study aimed to systematically review endocrine responses to intermittent fasting by examining appetite-regulating hormones (leptin, ghrelin), metabolic hormones (insulin), gastrointestinal hormones (GLP-1, PYY, CCK), and thyroid axis hormones across different protocols and populations [2,3]. Methods: A systematic review of 9 peer-reviewed articles (2020–2025) was conducted to examine hormonal responses to intermittent fasting [4,5]. Studies analyzed leptin and ghrelin secretion [4], insulin sensitivity [6,7], gastrointestinal hormones, and thyroid hormone metabolism with emphasis on hypothalamic–pituitary–thyroid axis regulation [8]. Results: Ghrelin increased during fasting [4,5], while leptin decreased, reflecting reduced adipose energy status [4]. Leptin reduction was associated with decreased thyroid-stimulating hormone and triiodothyronine, promoting energy conservation [8]. Insulin responses remained inconclusive, dependent on protocol, duration, meal timing, and individual characteristics [6,7,9]. Gastrointestinal hormones showed modest, context-dependent changes, varying across populations [3,10,11]. Thyroid hormone activity decreased peripherally, while the central axis remained stable, representing coordinated adaptive responses [1,8]. Conclusions: Intermittent fasting induces coordinated endocrine changes [1]. Ghrelin elevation and leptin reduction are consistent markers [4,5], while insulin responses show variability [6,7,9]. Heterogeneity reflects differences in fasting duration, protocols, and populations [3]. Time-restricted eating shows promise when aligned with circadian rhythms [2]. Future research with standardized methodologies is essential [1].
References
1. Karimi, R. et al. Adaptive effects of endocrine hormones on metabolism of macronutrients during fasting and starvation: A scoping review. Metabolites 2024, 14, 336, doi:10.3390/metabo14060336.
2. Kim, B. et al. Effects of intermittent fasting on the circulating levels and circadian rhythms of hormones. Endocrinol Metab (Seoul) 2021, 36, 745–756, doi:10.3803/EnM.2021.405.
3. Alogaiel, D.M. et al. Effects of Ramadan intermittent fasting on hormones regulating appetite in healthy individuals: A systematic review and meta-analysis. Clin Nutr 2025, 45, 250–261, doi:10.1016/j.clnu.2025.01.005.
4. Al-Rawi, N. et al. Effect of diurnal intermittent fasting during Ramadan on ghrelin, leptin, melatonin, and cortisol levels among overweight and obese subjects: A prospective observational study. PLoS One 2020, 15, e0237922, doi:10.1371/journal.pone.0237922.
5. Hollstein, T. et al. Effects of short-term fasting on ghrelin/GH/IGF-1 axis in healthy humans: The role of ghrelin in the thrifty phenotype. J Clin Endocrinol Metab 2022, 107, e3769–e3780, doi:10.1210/clinem/dgac353.
6. Faris, M.A. et al. A systematic review, meta-analysis, and meta-regression of the impact of diurnal intermittent fasting during Ramadan on glucometabolic markers in healthy subjects. Diabetes Res Clin Pract 2020, 165, 108226, doi:10.1016/j.diabres.2020.108226.
7. Lu, L. et al. The effect of intermittent fasting on insulin resistance, lipid profile, and inflammation on metabolic syndrome: A GRADE assessed systematic review and meta-analysis. J Health Popul Nutr 2025, 44, 293, doi:10.1186/s41043-025-01039-2.
8. Sui, X. et al. The influence of extended fasting on thyroid hormone: Local and differentiated regulatory mechanisms. Front Endocrinol 2024, 15, 1443051, doi:10.3389/fendo.2024.1443051.
9. Yuan, X. et al. Effect of intermittent fasting diet on glucose and lipid metabolism and insulin resistance in patients with impaired glucose and lipid metabolism: A systematic review and meta-analysis. Int J Endocrinol 2022, 2022, 6999907, doi:10.1155/2022/6999907.
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Copyright (c) 2026 Sofia João Nogueira, Suellen Nunes, Beatriz Campos, Ana Isa Silva
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