Betaine (Trimethylglycine): Benefits for Homocysteine and Muscle

A look at what betaine actually does in the body, and where the supplement evidence is solid versus shaky.

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By the Ration Editorial Team · Reviewed against primary research · Updated July 13, 2026

Betaine, also called trimethylglycine, is a naturally occurring compound found in beets, spinach, whole grains, and seafood.

Your body also makes it from choline through a series of reactions in the liver and kidneys.

Chemically, it is a modified form of the amino acid glycine, carrying three methyl groups that make it useful as a methyl donor.

Betaine's best understood job is donating a methyl group to convert homocysteine back into methionine, a reaction catalyzed by the enzyme betaine homocysteine methyltransferase (BHMT)^[9][12].

This remethylation pathway runs mainly in the liver and kidneys and works alongside the folate and vitamin B12 dependent pathway for homocysteine clearance^[12].

Betaine also acts as an osmolyte, helping cells retain water and withstand physical or metabolic stress. This is part of why it has been studied in sports nutrition and, more recently, in aging research^[1].

This is where the evidence for betaine is strongest. Elevated homocysteine has long been linked to cardiovascular and cognitive risk, and betaine supplementation has repeatedly been shown to bring levels down^[10][11].

Human trials, including in people with genetic conditions that cause very high homocysteine, show consistent reductions with betaine supplementation^[10].

Animal research adds a mechanistic angle: in one study, betaine reduced homocysteine-induced brain inflammation and protected cognitive function by calming a specific type of immune cell death in the brain called pyroptosis^[2].

A 2025 narrative review ties this homocysteine-lowering effect into broader theories about betaine and healthy aging, though the authors are careful to frame this as an emerging area rather than settled science^[1].

Betaine has a following in the gym supplement world, often included in pre-workout blends^[7].

The overall consensus across six data points, when aggregated, points toward an increase in lean body mass, earning a top evidence grade in our database.

• ↑Lean Body MassAHuman trials

  Research may raise Lean Body Mass · strong agreement · 6 studies

  View 5 studies on PubMed

  • Betaine supplementation fails to improve body composition: a systematic review and meta-analysis (2022)
  • Betaine and Soluble Fiber Improve Body Composition and Plasma Metabolites in Cats with Chronic Kidney Disease (2023)
  • The effects of chronic betaine supplementation on body composition and performance in collegiate females: a double-blind, randomized, placebo controlled trial (2018)
  • Effects of Betaine Supplementation on Markers of Metabolic Flexibility, Body Composition, and Anaerobic Performance in Active College-Age Females (2023)
  • Effects of betaine on performance and body composition: a review of recent findings and potential mechanisms (2014)
• ↓HomocysteineAHuman trials

  Research may lower Homocysteine · strong agreement · 6 studies

  View 5 studies on PubMed

  • Betaine and aging: A narrative review of findings, possible mechanisms, research perspectives, and practical recommendations (2025)
  • Betaine alleviates cognitive impairment induced by homocysteine through attenuating NLRP3-mediated microglial pyroptosis in an m(6)A-YTHDF2-dependent manner (2024)
  • Betaine homocysteine methyltransferase (BHMT)-dependent remethylation pathway in human healthy and tumoral liver (2013)
  • The use of betaine in the treatment of elevated homocysteine (2006)
  • Effects of betaine intake on plasma homocysteine concentrations and consequences for health (2005)

But it is worth being honest about what the individual trials actually show, because the picture is messier than a single grade suggests.

A 2023 randomized trial in active college-age women found some improvements in metabolic flexibility markers with betaine, but body composition changes were modest^[3].

An earlier trial in collegiate women over a longer supplementation period found little meaningful difference from placebo on body composition or performance^[6].

A systematic review and meta-analysis pooling this kind of trial concluded that betaine supplementation fails to meaningfully improve body composition, directly challenging the more optimistic older narrative reviews^[5][8].

Interestingly, one of the more consistent body composition benefits comes from an unexpected place: a veterinary trial in cats with chronic kidney disease, where betaine combined with soluble fiber improved body composition and metabolic markers^[4]. That is a different population entirely and should not be read as proof of similar effects in healthy humans.

Put together, betaine's reputation as a muscle building supplement outpaces what the human sports nutrition trials actually demonstrate.

• Beets (the richest common dietary source)
• Wheat bran and wheat germ
• Spinach
• Quinoa
• Shrimp and other shellfish
• Whole grain breads and cereals

Because betaine is so concentrated in beets, beet juice and beet powder are common ways people boost intake without using a standalone betaine supplement.

In homocysteine focused research, doses have generally landed in the range of 1.5 to 6 grams per day, often split into smaller doses^[10][11].

Sports nutrition trials testing lean mass and performance have typically used around 2.5 grams per day, taken for several weeks^[3][6].

Betaine is sold as trimethylglycine (TMG) powder or capsules, and is a common ingredient in multi-ingredient pre-workout formulas alongside creatine and caffeine^[7].

Betaine is generally regarded as safe at studied doses, including in long term clinical use for homocysteine management^[10].

Reported side effects are mostly mild and can include:

• Nausea or stomach upset, especially at higher doses
• Diarrhea
• A fishy body odor in some people
• Rare reports of elevated cholesterol markers at very high clinical doses^[10]

People combining betaine with other supplements in pre-workout blends should be mindful of cumulative ingredient effects rather than assuming each component is automatically safe in combination^[7].

• People with elevated homocysteine looking to support levels alongside standard care, ideally discussed with a clinician^[10][11]
• Researchers and clinicians tracking one-carbon metabolism and methylation status^[9][12]
• Athletes curious about pre-workout formulas, with realistic expectations about body composition effects^[5]
• People interested in aging and cognitive health research, an area still described as emerging^[1][2]

Betaine's homocysteine lowering effect is one of the better established actions of any common supplement, with decades of consistent human data behind it^[10][11][12].

Its reputation for building lean muscle mass is more complicated. While pooled data in our database leans positive, several well designed trials and a dedicated meta-analysis have failed to find meaningful body composition benefits in healthy adults^[5][6].

Anyone drawn to betaine for gym performance should treat it as a minor player at best, while its role in methylation and homocysteine metabolism remains its most credible claim to fame.