Betaine (TMG)

A compound also known as trimethylglycine (TMG), found in beets and produced by the body from choline. It plays two well-established roles. As an osmolyte it helps cells draw in and hold water, which pairs it naturally with electrolytes for hydration. As a methyl donor it helps convert homocysteine into methionine. Although it is structurally a modified amino acid, it is not a substrate for protein synthesis and does not trigger the insulin or mTOR response that breaks a fast. Research has instead linked it to AMPK, the energy-sensing pathway active while fasting.