David Sinclair is a Harvard professor who has spent 25 years studying why we age. His conclusion: aging is not inevitable decay — it's an information problem. Our cells contain the software to be young; they lose the ability to read it. His protocol is designed to keep that reading process intact for as long as possible.
This page covers his full published stack — NMN, resveratrol, TMG, and metformin — explains why the order and timing matter, and connects it to why tirzepatide users may already be activating some of the same longevity pathways through a different door.
NMN is a direct precursor to NAD+, the molecule that powers virtually every energy-producing reaction in your cells. NAD+ levels drop by roughly 50% between age 20 and 60. Without adequate NAD+, sirtuins — the proteins that repair DNA and regulate metabolism — cannot function. NMN raises NAD+ levels. Sinclair takes 1g daily, in the morning, fasted.
Resveratrol activates SIRT1 — the primary longevity sirtuin. It does not work well without fat present; it's fat-soluble and absorption from a fasted, fat-free state is nearly zero. Sinclair stirs his resveratrol powder into yogurt or takes it with a small amount of olive oil. The fat requirement is not optional.
When NMN is converted to NAD+, the process consumes methyl groups. Over time, high-dose NMN can deplete your methylation reserves. TMG donates methyl groups to offset this — it acts as a methylation buffer. Without it, chronic NMN supplementation may raise homocysteine levels. Sinclair added TMG after this concern emerged in the research community.
Metformin is a prescription diabetes drug with a strong longevity research record. It activates AMPK — an enzyme that signals cellular stress and triggers repair, mitophagy, and fat burning. Sinclair takes it with dinner specifically because metformin blunts the anabolic signal from exercise if taken beforehand. Evening dosing sidesteps this conflict entirely.
Sinclair skips breakfast (intermittent fasting to trigger AMPK and maintain a low insulin state), uses cold showers or brief ice baths for hormetic stress, and uses red/near-infrared light panels for mitochondrial support. He also takes vitamin D3+K2, low-dose aspirin, and quercetin — though these are secondary to the core stack above.
Your body has a master repair system. It runs on a fuel called NAD+. When you're 20, you have a full tank. By 50, it's half empty. By 70, it's nearly gone. When NAD+ runs low, your DNA repair slows, your mitochondria break down, and you age faster.
Sinclair's protocol tries to solve this from multiple angles at once:
NAD+ Decline Rates: NAD+ levels in human tissue decline approximately 1–2% per year after age 30, with sharp acceleration after 50. Skeletal muscle, liver, and brain show the steepest declines. The primary driver is increased consumption by CD38 (an NADase) and PARP enzymes responding to accumulating DNA damage — not reduced synthesis. NMN bypasses the rate-limiting step in NAD+ synthesis (NAMPT pathway), providing substrate directly.
Sirtuin Activation: SIRT1 is an NAD+-dependent deacetylase that regulates PGC-1α (mitochondrial biogenesis), FOXO transcription factors (stress resistance, apoptosis), and p53 (DNA repair). Resveratrol acts as a STAC (sirtuin-activating compound), lowering the activation threshold for SIRT1 in the presence of its substrate. The combination of NMN (increasing NAD+ substrate) and resveratrol (lowering the activation barrier) is synergistic rather than additive.
AMPK Pathway: Metformin inhibits Complex I of the mitochondrial electron transport chain, mildly reducing ATP production and raising the AMP:ATP ratio. This activates AMPK, which in turn suppresses mTORC1 (reducing anabolic/growth signaling), activates ULK1 (autophagy initiation), and phosphorylates TFEB (lysosomal biogenesis). The net effect is a cellular "maintenance mode" analogous to caloric restriction.
Exercise Conflict: Resistance training generates a post-exercise AMPK signal followed by a critical mTOR rebound responsible for muscle protein synthesis. Metformin taken within 4 hours of exercise blunts this mTOR rebound (Merry & Ristow, 2016; Konopka et al., 2019). Sinclair's evening dosing preserves the anabolic window from morning or afternoon training while still capturing the overnight AMPK-driven repair effects.
Methylation Consideration: NMN→NAD+ conversion via the salvage pathway generates nicotinamide (NAM), which is cleared via NNMT-mediated methylation consuming S-adenosylmethionine (SAM). Chronic high-dose NAM without methyl donor supplementation can increase homocysteine and deplete SAM-dependent methylation for other substrates (including DNA methylation, neurotransmitter synthesis). TMG provides trimethyl glycine as a methyl donor through the BHMT pathway, independent of the folate cycle — making it the most direct cofactor to pair with NMN.
Here's what most tirzepatide users don't realize: they may already be activating AMPK through their medication and eating pattern. Tirzepatide's GLP-1 agonism improves insulin sensitivity and reduces hyperinsulinemia — the state of chronically elevated insulin that actively suppresses AMPK. Add OMAD or intermittent fasting on top, and you have extended periods of low insulin, low glucose, and elevated glucagon — all of which are physiological AMPK activators.
Sinclair's metformin does pharmacologically what tirzepatide + fasting does through food behavior and hormonal signaling. They converge on the same cellular switch. If you're already on tirzepatide and eating one meal a day, you are running a meaningful degree of the Sinclair protocol without knowing it.
Adding NMN + resveratrol + TMG on top of a tirzepatide protocol is therefore a logical extension — you're already activating the energy-sensing pathways; you're now also providing the raw substrate (NAD+) and the activating compounds (resveratrol) to run the repair machinery at full capacity.
Morning (fasted): NMN 1g + TMG 500mg + Resveratrol 1g WITH a small amount of fat (1 tbsp yogurt, olive oil, or a few bites of avocado).
Evening (with dinner): Metformin 500–800mg (prescription required).
Skip breakfast to extend the low-insulin / AMPK-active window.
Do not take metformin within 4 hours of a workout.
See also: Complete Supplement Stack · NMN Complete Guide · Gary Brecka's Methylation Protocol