What Is TMG (Trimethylglycine)?

Reviewed by SOMA HEALTH's Medical Research Team

TMG – trimethylglycine, also known as betaine – has become the quiet companion in a lot of longevity stacks, especially among people taking NMN. Its job description sounds abstract: it is a ‘methyl donor’ that ‘supports methylation.’ This guide translates that into plain language: what TMG is, why the NMN crowd reaches for it, what human research actually shows about homocysteine, the honest caveats, and how it differs from a mitochondrial compound like urolithin A.

What TMG is

TMG stands for trimethylglycine: a molecule of the amino acid glycine carrying three methyl groups. It is chemically identical to betaine, a name that comes from sugar beets, where it was first identified. Beyond beets, TMG occurs naturally in spinach, quinoa, whole grains, and shellfish. In the body it plays two established roles – it acts as an osmolyte (helping cells manage water balance) and, more relevant here, as a donor of methyl groups.

A ‘methyl group’ is just a small carbon-and-hydrogen unit (–CH₃) that the body moves from one molecule to another. This constant shuttling of methyl groups – collectively called methylation – is involved in an enormous range of housekeeping: building and regulating DNA, making neurotransmitters and creatine, and processing certain amino acids. TMG’s value is that it can hand off one of its three methyl groups when the body needs one.

Methylation and homocysteine: the core mechanism

The clearest, best-established role for TMG involves an amino acid called homocysteine. Homocysteine is a normal metabolic intermediate, but when it accumulates it is considered an unfavorable marker. The body has more than one way to clear it. One route uses folate and vitamin B12. A parallel route uses TMG: through an enzyme called betaine-homocysteine methyltransferase (BHMT), TMG donates a methyl group to convert homocysteine back into methionine, a useful amino acid. In effect, TMG helps recycle homocysteine rather than letting it pile up.

This is not a fringe hypothesis. Human trials have consistently shown that betaine (TMG) supplementation lowers blood homocysteine. That is one of the most reproducible findings in this ingredient category. Supporting healthy homocysteine metabolism through methylation is the structure/function claim TMG can legitimately stand behind – while being clear that lowering a lab marker is not the same as treating or preventing cardiovascular disease, which is a matter for your physician.

Why the NMN crowd takes TMG

Here is where TMG intersects with the NAD-boosting world. When the body processes and eventually excretes nicotinamide (a form of vitamin B3 closely related to NMN and NR), it often attaches a methyl group first – a step carried out by an enzyme called NNMT. The concern, popular in supplement circles, is that taking large amounts of NAD precursors could increase methyl-group consumption and, over time, draw down the body’s methyl pool, potentially nudging homocysteine upward. TMG is added as insurance: a readily available methyl donor to keep the tank topped up.

It is worth being precise about how solid this reasoning is. The biochemistry is real, and the logic is coherent. But the claim that NMN meaningfully depletes methyl groups in humans, and that TMG is therefore necessary alongside it, has not been firmly established in human trials – it remains a sensible precaution more than a proven requirement. TMG’s homocysteine-lowering effect stands on its own regardless of whether you take NMN.

The honest caveat: blood lipids at higher doses

TMG is not consequence-free, and a responsible overview has to say so. Randomized, placebo-controlled research on homocysteine-lowering nutrients in healthy people found that betaine supplementation, while reliably lowering homocysteine, was associated with increases in LDL and total cholesterol – an effect seen more at higher doses. This is a recurring theme with methyl-related compounds: a favorable move in one marker can come with an unfavorable move in another. It is a strong argument for using modest doses, not mega-doses, and for actually monitoring your bloodwork rather than assuming benefit. This is guidance to discuss with your doctor, not a treatment plan.

How TMG compares to urolithin A

People often lump TMG and urolithin A together as ‘healthy aging’ supplements, but they work on entirely different problems. TMG is about methyl chemistry and homocysteine. Urolithin A is about mitochondria – specifically mitophagy, the process by which cells identify and recycle worn-out mitochondria so fresher, more efficient ones can take their place. Urolithin A is a gut postbiotic your microbiome produces from ellagitannins in pomegranate, walnuts, and berries, but only some people carry the microbes that convert it well, which is why many choose to supplement it directly.

The human evidence for urolithin A is comparatively developed. In humans, Andreux and colleagues (2019, Nature Metabolism) reported the first-in-human study and found it safe and well tolerated up to 1,000 mg per day, alongside a mitochondrial gene-expression signature. Randomized human trials – Liu and D’Amico (2022, JAMA Network Open) in older adults and Singh and colleagues (2022, Cell Reports Medicine) in middle-aged adults using 500 mg and 1,000 mg arms – looked at muscle endurance, strength, and exercise performance, and a 2025 Nature Aging randomized trial reported support for immune-cell mitochondrial health in midlife adults. The foundational mitophagy and lifespan work (Ryu and colleagues, 2016, Nature Medicine) is preclinical, established in C. elegans and rodents. For the full picture, read our complete urolithin A guide, compare options in our best urolithin A gummies roundup, and see the everyday takeaways in our urolithin A benefits overview and mitochondrial health primer.

Practical notes if you are considering TMG

For general methylation and homocysteine support, TMG is commonly used in the range of roughly 500 to 1,000 mg per day, while the larger doses studied for homocysteine (and linked to the lipid caveat above) are several grams – check the current label of any product for exact amounts. TMG pairs conceptually with adequate folate and B12, since those run the parallel homocysteine pathway. It is generally well tolerated; higher doses can cause digestive upset or, in some people, a ‘fishy’ body odor from a related metabolite. If you have a cardiovascular or kidney condition, are pregnant or nursing, or take medications, speak with a qualified healthcare provider before starting. TMG supports normal methylation; it is not a treatment for high homocysteine, heart disease, or any other condition.

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. This guide is educational and is not a substitute for advice from a qualified healthcare provider.