Cycling oral NAD+ precursors (NR/NMN) in sync with short fasting-mimicking cycles will increase nuclear SIRT1 deacetylase activity in human peripheral blood mononuclear cells compared with continuous dosing.

Rationale

• Both NR and NMN raise blood NAD+ ~2‑fold but do not reliably increase brain NAD+ after 8 days【1】【2】.
• Oral dosing leads to extensive hepatic conversion to nicotinamide, which feeds back to inhibit NAMPT and limits organ‑specific NAD+ synthesis【5】.
• Short fasting periods suppress hepatic nicotinamide N‑methyltransferase (NNAT) and up‑regulate NAMPT, relieving this feedback block【6】.
• In mice, NMN‑driven neuroprotection requires Sirt1, showing the pathway is functional when NAD+ reaches the nucleus【4】.
• No human study has compared cycling versus continuous NAD+ precursor regimens, nor examined timing relative to fasting‑mimicking diets.

Novel Mechanistic Insight We propose that a fasting‑mimicking window lowers circulating nicotinamide and hepatic NNAT activity, thereby decreasing the inhibitory tone on the salvage pathway. When NR or NMN is administered during the subsequent refeeding phase, the elevated NAMPT activity drives faster conversion to NAD+ in peripheral immune cells, increasing the NAD+/NAM ratio and promoting nuclear SIRT1 activation. Continuous dosing, by contrast, maintains high nicotinamide levels that sustain feedback inhibition, blunting tissue NAD+ accrual despite blood elevations.

Testable Predictions

1. Participants undergoing a 5‑day fasting‑mimicking diet followed by 2 days of NR/NMN supplementation will show a ≥1.5‑fold increase in nuclear SIRT1 activity (measured by acetyl‑p53 deacetylation) in PBMCs relative to a continuous NR/NMN arm receiving the same total weekly dose.
2. The cycling arm will exhibit a higher NAD+/NAM ratio in isolated PBMCs and a reduction in hepatic NNAT expression (via circulating miR‑122‑5p surrogate) compared with the continuous arm.
3. Mitochondrial respiration (OCR) in PBMCs will rise ≥20 % only in the cycling condition, linking SIRT1 activation to functional outcomes.

Experimental Design

• Randomized crossover trial, n=30 healthy adults.
• Arm A: continuous NR 300 mg bid (total 1200 mg/day) for 14 days.
• Arm B: 5‑day fasting‑mimicking diet (≈50 % kcal) days 1‑5, then NR 300 mg bid days 6‑7; repeat for two weeks.
• Washout 4 weeks between arms.
• Primary outcome: nuclear SIRT1 activity in PBMCs (immunoprecipitated SIRT1 deacetylase assay).
• Secondary outcomes: PBMC NAD+ and NAM levels (LC‑MS/MS), NAD+/NAM ratio, hepatic NNAT surrogate (plasma miR‑122‑5p), PBMC OCR (Seahorse).

Potential Outcomes If the hypothesis is correct, the cycling regimen will demonstrate superior SIRT1 activation and mitochondrial improvements despite identical total precursor exposure, falsifying the notion that blood NAD+ elevation alone predicts tissue sirtuin activity. A null result would support the view that precursor dosing timing relative to fasting does not overcome hepatic salvage constraints, directing future work toward alternative delivery strategies (e.g., nanoparticle‑encapsulated NR or direct NAD+ precursors).

References [1] https://www.nad.com/news/nr-raises-nad-over-2-fold-more-than-nmn-new-study-comparing-nad-precursors [2] https://renuebyscience.com/pages/a-current-list-of-completed-nmn-human-trials [3] https://www.innerbody.com/nmn-vs-nr [4] https://www.frontiersin.org/journals/pharmacology/articles/10.3389/fphar.2025.1545585/full [5] https://www.foundmyfitness.com/episodes/nad-flux-metabolism [6] https://pmc.ncbi.nlm.nih.gov/articles/PMC9289528/