Hormonal
Fasting (1-5 days) significantly increases growth hormone (GH) secretion in humans by increasing both pulse frequency and amplitude, and reveals underlying ultradian and circadian rhythmicity that is masked in the fed state.
If you fast for 1-5 days, your body significantly increases Growth Hormone output. This isn't just random; it reveals hidden daily (circadian) and shorter (ultradian) rhythms. This hormonal shift helps your body switch from burning sugar to burning fat, which helps preserve muscle mass during the fast. However, note that while GH goes up, the actual growth factor (IGF-1/SmC) goes down, so fasting is for metabolic flexibility, not building new muscle tissue.
The 5-d fast resulted in a significant increase in discrete GH pulse frequency (5.8±0.7 vs. 9.9±0.7 pulses/24 h, P = 0.028), 24 h integrated GH concentration (2.82±0.50 vs. 8.75±0.82 g min/ml; P = 0.0002), and maximal pulse amplitude (5.9±1.1 vs. 12.3±1.6 ng/ml, P < 0.005).
Why this rating
Small sample size (n=6), controlled clinical setting, but rigorous time-series analysis methods.
Source
Fasting enhances growth hormone secretion and amplifies the complex rhythms of growth hormone secretion in man.
K. Ho et al. · Journal of Clinical Investigation · 1988
DOI 10.1172/jci113450
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