Intermittent Fasting
The eating window that activates autophagy, sirtuins, and cellular repair
Definition
Intermittent fasting (IF) is an eating pattern that alternates periods of fasting with feeding windows. The most-studied protocols are 16:8 (16 h fast, 8 h eating window), 18:6, 20:4 (warrior diet), 5:2 (two days of very low intake per week), and alternate-day fasting. More than a diet, it is a chronobiological pattern that activates longevity pathways — autophagy, AMPK, sirtuins — by inhibiting mTOR during the fasting phase.
Detailed explanation
Fasting for 12-16 h progressively activates lipolysis and hepatic ketogenesis; from 16-18 h, autophagy intensifies; beyond 24-48 h, the first significant peaks of growth hormone appear (up to 5× baseline) and mTORC1 is deeply inhibited. The fundamental metabolic shift is the 'metabolic switch' from glucose to ketones described by Mark Mattson (NIH).
Human studies published in NEJM (Mattson 2019) and Cell Metabolism show improvements in insulin sensitivity, blood pressure, lipid profile, inflammatory markers, and body composition. Time-restricted eating (TRE) — even without caloric restriction — improves the metabolic circadian rhythm by aligning food intake with daylight.
Relative contraindications: pregnancy, breastfeeding, eating disorders, athletes in active hypertrophy phase, type 1 diabetics without medical supervision, and people with low weight or sarcopenia. In premenopausal women, it is advisable to monitor the menstrual cycle and avoid prolonged fasts in the late luteal phase.
Scientific sources
- PubMed — Effects of intermittent fasting on health, aging, and disease (Mattson, NEJM)
- PubMed — Early time-restricted feeding improves insulin sensitivity in prediabetes
- PubMed — Flipping the metabolic switch: understanding intermittent fasting
- PubMed — Fasting: molecular mechanisms and clinical applications
Related terms
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