Metabolic biomarker improvement plateaus at 16:8. Stricter windows increase cortisol without additional metabolic benefit — the Salk Institute's 12-week RCT makes this case compellingly.
The Three Windows Compared
- 16:8: Fasting insulin reduced 18%, HOMA-IR improved 22%, no cortisol elevation
- 18:6: Fasting insulin reduced 19%, HOMA-IR improved 23%, cortisol +8% (NS)
- OMAD: Fasting insulin reduced 17%, HOMA-IR improved 19%, cortisol +31% (p=0.003), lean mass loss detected
The Dose-Response Breaks
The data shows a clear dose-response break between 18:6 and OMAD. The additional 6-hour restriction of OMAD adds physiological stress without adding metabolic benefit — and the lean mass signal is a concern for longevity-focused practitioners.
