Hypothesis

Intermittent fasting (IF) triggers a hormetic stress response that improves healthspan but simultaneously activates DNA‑damage‑response pathways, causing a short‑term increase in epigenetic‑clock age that does not reflect accelerated biological aging.

Mechanistic Basis

IF cycles of nutrient deprivation activate AMPK and SIRT1, leading to increased NAD+ levels and enhanced PARP‑mediated DNA repair. PARP activity consumes NAD+ and generates poly‑ADP‑ribose chains that recruit chromatin‑remodeling complexes, altering DNA methylation at CpG sites used by epigenetic clocks Salk Institute. These changes mimic age‑related methylation shifts, raising clock readouts. Concurrently, IF‑induced autophagy and mitochondrial hormesis improve cellular function, extending healthspan Frontiers in Aging. Thus, clocks may capture a transient repair signature rather than true aging.

Testable Predictions

1. In healthy humans undergoing a 12‑week IF regimen, epigenetic age measured by Horvath’s clock will rise significantly after the first two weeks, then return to baseline by week 12 despite continued improvement in insulin sensitivity, VO₂max, and inflammatory markers.
2. Pharmacological inhibition of PARP (e.g., with olaparib at low dose) during IF will blunt the epigenetic‑age rise without abolishing the metabolic benefits of IF.
3. Mouse models subjected to IF will show increased γH2AX foci and elevated methylation at clock CpGs in liver tissue after one week, correlating with improved grip strength and glucose tolerance.

Experimental Design

• Human trial: 60 participants aged 45‑65, randomized to IF (16:8) or control diet for 12 weeks. Blood draws at baseline, week 2, week 6, week 12 for epigenetic‑clock analysis (Illumina EPIC array), metabolic panel, and cytokine profile. A subset receives low‑dose olaparib or placebo double‑blinded PMC12714307.
• Mouse study: C57BL/6J males, 10 months old, assigned to IF (alternate‑day fasting) or ad libitum for 4 weeks. Tissue collected at 1 wk, 2 wk, 4 wk for bisulfite sequencing of clock CpGs, γH2AX immunostaining, and functional tests (rotarod, GTT) PMC4215333.

Potential Implications

If confirmed, this hypothesis would explain why many “age‑reversal” interventions improve biomarkers without extending lifespan in mice, and why epigenetic clocks can penalize beneficial stress‑response pathways Aging US. It would shift the field toward using dynamic, multi‑omic readouts that separate damage signals from repair activity, improving the validity of surrogate endpoints for gerotherapeutic trials PMC9768060.