Growth hormone increases significantly during fasting—sometimes 2-5 times baseline levels within 24-48 hours. Research by Ho and Hartman found five-fold increases during 40-hour fasts. GH is powerfully muscle-preserving, signaling the body to maintain lean tissue while burning fat for fuel. This is why fasting doesn’t cause the muscle loss that simple calorie restriction might—the hormonal environment is different.
This companion covers what growth hormone does, the fasting effect on GH secretion, why this matters for muscle preservation, and practical implications for intermittent fasting and exercise. (4 min read)