Trimethylglycine (TMG), also known as glycine betaine, refers to three methyl groups attached to a molecule of glycine. In the 1950s, TMG was discovered to be beneficial to the heart and it functions in a similar way to vitamin B12.

As a methyl donor, it provides methyl groups to other bodily molecules. When a TMG methyl group is donated to a molecule of homocysteine, the cardiovascular risk factor is converted back to the beneficial amino acid, methionine. While working to promote healthy levels of homocysteine, alone or in conjunction with other nutrients, it has been attested as an important nutrient for cardiovascular health.