Betaine Anhydrous (TMG): What the Research Actually Shows

Betaine anhydrous — usually sold under its older name, trimethylglycine (TMG) — is a compound your body already makes from choline, and one you already eat in small amounts from beets, spinach, and whole grains. It has two separate, well-documented jobs: donating methyl groups to lower homocysteine, and drawing water into muscle cells during training. Most of the marketing around it blurs these two effects together. The research treats them separately, and so should you.

The Methylation Mechanism

Betaine's primary biochemical role is as a methyl donor in the liver and kidneys. The enzyme betaine-homocysteine methyltransferase (BHMT) uses betaine to convert homocysteine back into methionine, which then goes on to form S-adenosylmethionine (SAMe) — the body's main methyl donor for hundreds of reactions, including neurotransmitter synthesis and DNA regulation. This pathway runs independently of the folate-and-B12 remethylation cycle, which is why betaine is sometimes used clinically alongside those nutrients rather than instead of them.

What the Homocysteine Data Shows

Elevated homocysteine is an independent risk marker for cardiovascular disease, and betaine's effect on it is one of the more consistently replicated findings in nutrition research. Randomized controlled trials summarized in the American Journal of Clinical Nutrition and related homocysteine-lowering trials found that betaine supplementation reduces fasting plasma homocysteine by roughly 12–20 percent, and blunts the post-methionine-load spike by 20–40 percent in healthy adults. The mechanism is direct: more substrate for BHMT means faster conversion of homocysteine to methionine.

There's a documented tradeoff worth knowing before you supplement long-term: several of the same trials found that betaine modestly raised LDL cholesterol and triglycerides in healthy participants, which partially offsets the cardiovascular benefit of lowering homocysteine. This isn't a reason to avoid it outright, but it's a reason to treat betaine as a targeted intervention — useful if your homocysteine is actually elevated — rather than a blanket daily supplement.

The Exercise Performance Evidence

The second body of research looks entirely different. A study published in the Journal of the International Society of Sports Nutrition gave experienced strength-trained men 2.5g of betaine daily for six weeks and found significant increases in lean mass and reductions in fat mass compared to placebo, along with improved bench press training volume in the early and late microcycles. A separate trial in resistance-training-naive women found similar improvements in body composition and work capacity over nine weeks, though strength and power gains were less consistent. Betaine appears to work here through cellular hydration and osmolytic effects on muscle tissue, plus its role in creatine and carnitine synthesis — a completely different mechanism from the homocysteine story.

Dosing

For methylation support, clinical trials typically use 1.5–3g of betaine anhydrous per day, split into two doses with meals. For performance goals, the studied dose is more consistent: 2.5g per day, taken with or without food, for at least two to six weeks before evaluating results. Products like NOW Foods TMG Betaine 1000mg make it straightforward to hit either range with one to three tablets daily.

Betaine Anhydrous vs. Betaine HCl

This distinction trips up a lot of buyers. Betaine hydrochloride (HCl) is a digestive supplement used to raise stomach acidity and is not interchangeable with betaine anhydrous (TMG) for methylation or performance purposes. Read the label carefully — if a product is marketed for "digestion" or paired with pepsin, it's the wrong form. Look specifically for "betaine anhydrous" or "trimethylglycine," ideally from a third-party tested brand like Nutricost.