Définition
TMG (trimethylglycine, also called betaine) is a compound that donates methyl groups through the BHMT pathway — an alternative to the folate-dependent methylation cycle. It supports homocysteine clearance, liver health, and exercise performance. Particularly useful for people with MTHFR variants.
TMG is naturally found in beets, spinach, quinoa, and whole grains. Its molecular structure is glycine with three methyl groups attached — hence trimethylglycine. TMG donates one of these methyl groups to homocysteine through BHMT (betaine-homocysteine methyltransferase), converting homocysteine back to methionine. This is an alternative to the folate/B12-dependent pathway and is particularly active in the liver.
The benefits of TMG supplementation are several. For methylation support, it provides an alternative homocysteine clearance route, making it particularly useful for individuals with MTHFR variants where the folate pathway is compromised. For liver health, betaine supports fatty liver resolution — multiple trials have shown TMG reduces hepatic fat content in non-alcoholic fatty liver disease. For exercise performance, TMG has modest but consistent evidence for supporting muscle endurance and recovery through its role as an osmolyte.
TMG also has specific relevance to NAD+ research protocols. When high-dose NAD+ precursors are used, they can consume methyl groups (through methylation and excretion of nicotinamide), potentially straining overall methylation capacity. Co-supplementation with TMG replenishes the methyl group pool — a common addition to longevity protocols.
Typical dosing is 500–2000mg daily. Higher doses (up to 6g) have been used in liver protocols but can lower circulating fat levels inappropriately and are generally not needed. TMG is well-tolerated and inexpensive. For women in methylation support protocols, TMG alongside methylfolate, methylcobalamin, and B6 forms a conservative and effective stack for lowering homocysteine.
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