Hypothesis

Combining daily time-restricted eating (TRE) with a weekly 24‑hour fast produces a synergistic increase in mitochondrial turnover that exceeds the effect of either regimen alone.

Mechanistic Rationale

It's known that daily TRE activates AMPK and SIRT1, driving PGC1α‑mediated mitochondrial biogenesis and basal mitophagy. A weekly 24‑hour fast deepens NAD+ accumulation, which potentiates SIRT3 activity and promotes deacetylation of mitochondrial enzymes, enhancing oxidative phosphorylation efficiency. Simultaneously, the prolonged fasting interval suppresses mTORC1 more profoundly, triggering TFEB nuclear translocation and lysosomal biogenesis. The combined effect raises both the supply of healthy mitochondria (via biogenesis) and the capacity to degrade damaged organelles (via mitophagosome‑lysosome fusion), creating a futile cycle that improves net mitochondrial quality.

Testable Predictions

1. In human skeletal muscle, the combined TRE + 24 h fast protocol will increase mitochondrial DNA copy number and citrate synthase activity more than TRE alone or 24 h fast alone after 8 weeks.
2. Lysosomal markers (LAMP1, CTSB) and TFEB nuclear localization will be higher in the combined group than in either single intervention.
3. Mitophagy flux, measured by mt‑Keima assay, will show a supra‑additive increase only in the combined condition.
4. Participants receiving the combined protocol will display greater improvements in VO₂ max and insulin sensitivity than those on TRE or periodic fasting alone.

Experimental Design

• Randomize overweight adults (n = 120) into four groups: control (usual diet), TRE only (10 h eating window daily), 24 h fast only (one 24‑h fast per week), and combined (TRE + weekly 24 h fast).
• Intervene for 8 weeks, prescribing isocaloric diets to isolate timing effects.
• Collect muscle biopsies at baseline and week 8 for:
  • Mitochondrial content (mtDNA copy number, citrate synthase)
  • Lysosomal biogenesis (LAMP1 immunostaining, TFEB subcellular fractionation)
  • Mitophagy flux (mt‑Keima fluorescence ratio)
  • SIRT3 activity (Western blot for deacetylated SOD2)
• Perform aerobic fitness test (VO₂ max) and oral glucose tolerance test at both time points.
• Statistical analysis: two‑way ANOVA with factors TRE and periodic fast, testing for interaction effects (synergy).

If the interaction term is significant for mitochondrial content, lysosomal markers, and mitophagy flux, the hypothesis is supported; absence of interaction refutes the proposed synergy.