What Is TMG (Trimethylglycine) and Why Every Serious NMN Stack Needs It

Ingredient Guide · Updated June 2026

Pick up most NMN supplements in Australia and read the label. Plain NMN, 500mg. Sometimes Resveratrol. Occasionally B12. Almost never TMG. And yet David Sinclair — the Harvard researcher most responsible for mainstream NMN awareness — takes TMG alongside NMN every day. His lab understood something that most supplement brands either don't know or don't want to explain: NMN supplementation at therapeutic doses consumes methyl groups, and without replenishment, this is a long-term problem.

What TMG Actually Is

TMG stands for Trimethylglycine — also known as betaine. It is a naturally occurring compound found in beets (the richest dietary source), spinach, quinoa, wheat germ, and shellfish. You consume small amounts of it in a normal diet.

TMG is a methyl donor. It can donate one of its three methyl groups (CH₃ — carbon with three hydrogen atoms) to other molecules in cellular reactions. Methyl groups are central to one of the most important regulatory systems in biology: the methylation cycle.

The Methylation System and Why NMN Depletes It

Methylation is the process by which methyl groups are added to DNA, proteins, and other molecules. It regulates gene expression, neurotransmitter synthesis, detoxification, immune function, and dozens of other biological processes. The methylation cycle requires a steady supply of methyl groups — sourced from dietary compounds like TMG, choline, folate, and B12.

Here is the NMN-methylation connection that most brands skip:

The pathway by which NMN becomes NAD+ — the NAD+ salvage pathway — involves an enzyme called NNMT (Nicotinamide N-methyltransferase). This enzyme methylates nicotinamide during the conversion process, consuming a methyl group per conversion. At 500mg NMN daily, the cumulative methyl consumption is clinically significant over weeks and months.

This does not mean NMN is dangerous. It means NMN at therapeutic doses requires methyl group replenishment — which is exactly what TMG provides. Without replenishment, the methyl pool gradually depletes. With TMG, the methyl pool remains stable and the NMN conversion can continue efficiently.

What Depleted Methylation Actually Means in Practice

If methylation capacity declines — because NMN is consuming methyl groups faster than your diet and endogenous synthesis can replenish them — several downstream processes are affected:

• Homocysteine accumulation: Homocysteine is converted to methionine via a methylation reaction. When methyl groups are depleted, homocysteine accumulates. Elevated homocysteine is associated with cardiovascular disease risk and cognitive decline.
• Epigenetic disruption: DNA methylation regulates gene expression. Depleted methyl groups can disrupt normal methylation patterns on DNA, potentially affecting which genes are expressed or silenced.
• Neurotransmitter impairment: The synthesis of serotonin, dopamine, and other neurotransmitters requires methylation reactions. Depleted methylation can affect mood and cognitive function.
• Liver function: Liver cells depend heavily on methylation for detoxification processes. Chronic methyl depletion can impair hepatic function over time.

How TMG Solves the Problem

TMG donates a methyl group in the reaction that converts homocysteine to methionine — the BHMT (Betaine-Homocysteine Methyltransferase) pathway. This reaction serves two functions simultaneously:

1. It reduces homocysteine — the cardiovascular and cognitive risk marker that accumulates without adequate methyl supply
2. It produces methionine — which enters the methyl cycle to regenerate SAM (S-adenosylmethionine), the universal methyl donor that all methylation reactions depend on

In plain terms: TMG keeps the methyl pool topped up, keeps homocysteine low, and ensures the NMN-to-NAD+ conversion does not gradually deplete a foundational cellular system.

TMG's Other Benefits

Beyond its methylation role, TMG has supporting evidence for:

• Exercise performance: Multiple trials show TMG at 2–2.5g daily improves muscular endurance and power output — likely via osmolytic effects and methyl donation to creatine synthesis
• Liver health: TMG is used clinically for non-alcoholic fatty liver disease (NAFLD) — betaine anhydrous (another name for TMG) reduces hepatic fat accumulation in supplementation studies
• Cardiovascular protection: Homocysteine reduction from TMG supplementation is associated with reduced cardiovascular risk markers
• Safety: TMG has an excellent safety profile. It is GRAS (Generally Recognised as Safe) in the US, and long-term use at 3–6g daily in clinical trials has shown no significant adverse effects

Dose Guide by NMN Level

FAQ

References: Olthof MR et al., J Nutr (2003) — TMG and homocysteine; Cholewa JM et al., J Int Soc Sports Nutr (2017) — TMG exercise performance; Lieber CS — alcohol, NNMT, and methyl depletion; Sinclair DA, Lifespan (2019). Not medical advice.