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This is general information, not medical advice. Supplements can interact with medicines and aren’t suitable for everyone, especially in pregnancy or with a medical condition. Talk to a pharmacist or doctor before starting one.
What it is
Betaine, also called trimethylglycine (TMG), is a derivative of the amino acid glycine. It is found in beetroot, spinach, quinoa and wheat products.
In the body it acts as a methyl donor, helping convert homocysteine to methionine, and as an osmolyte that helps cells hold water under stress.
It is sold as a supplement for heart health markers, liver health and exercise performance. Do not confuse it with betaine HCl, which is a stomach-acid supplement.
How it works
Betaine donates a methyl group to convert homocysteine into methionine, a pathway that is separate from the folate-dependent one. As an osmolyte it may protect cells from dehydration and stress, which is a proposed route for effects on exercise.
What the evidence says
- Strong Lowering homocysteine
Reliably lowers blood homocysteine; whether this improves health outcomes is not clearly shown. - Limited Muscle strength and power
Some studies show small improvements in power or volume of work; others show none. - Limited Body composition
Mixed results, with inconsistent changes in fat or lean mass. - Limited Liver health markers
Early research in fatty liver is mixed and not conclusive.
Evidence ratings are our plain-English summary of how much good human research exists, not a promise of results. How we rate evidence.
Dosage and timing
- Performance studies commonly use 2.5 g a day, or up to about 6 g split across the day.
- Homocysteine studies often use 4-6 g daily under clinical supervision.
- Take with food to reduce stomach upset.
- No official UK upper limit that is widely established; check current guidance. High-dose use should be discussed with a clinician.
Forms and what to look for
- Betaine anhydrous (TMG) is the form used in studies.
- Betaine HCl is a different product used to supply stomach acid; it is not interchangeable.
- Powder is cheap and dissolves easily, but taste is mildly sweet-salty.
- Check the label lists grams of betaine per serving.
What to expect, and when
- Homocysteine can fall within a few weeks.
- Any performance effects are modest and may need several weeks of consistent use.
- Many people notice nothing.
Side effects
- Nausea, stomach discomfort or diarrhoea.
- Fishy body odour at high doses.
- Raised LDL cholesterol has been seen at higher doses in some studies.
- Rarely, dizziness.
Interactions
- Methionine supplements: may raise homocysteine in some contexts when combined.
- Medicines affecting homocysteine or methylation: ask a pharmacist or clinician.
- Cholesterol-lowering medicines: monitor lipids if using high-dose betaine.
- Other methyl donors such as SAMe: combined effects not well studied.
Who should avoid it
- People with homocystinuria should only use it under specialist care.
- People with high LDL cholesterol or on lipid medicines, unless advised.
- Pregnancy and breastfeeding: not enough evidence for high doses.
- People with kidney disease, without medical advice.
Risks and safety
- High doses may raise LDL cholesterol.
- Long-term high-dose safety is not well established.
- Not on the WADA prohibited list.
- Do not confuse with betaine HCl: taking the wrong one can mean the wrong effect and dose.
Buying well: quality and testing
- Choose products labelled betaine anhydrous or trimethylglycine with grams per serving.
- Third-party testing (Informed Sport, NSF) is a plus.
- Avoid blends hiding the betaine dose.
- Check it is not betaine HCl unless that is what you want.
Bottom line
Betaine reliably lowers homocysteine and has some interest from sport, but the performance evidence is inconsistent. It may suit people with raised homocysteine under a clinician's advice, or athletes who want to experiment cautiously. Keep an eye on cholesterol if you use higher doses regularly.