Research dossier
Clinical research on TMG (Trimethylglycine)
8 trials reviewed across 5 indications.
Strongest evidence
Homocystinuria (the one FDA-approved use)
Mechanism
In the inherited disease homocystinuria (e.g. CBS deficiency), betaine remethylates the dangerously elevated homocysteine, substantially lowering plasma levels and reducing thromboembolic risk.
Worth stating clearly: prescription betaine anhydrous (Cystadane®) is FDA-approved for inherited homocystinuria, where it meaningfully lowers homocysteine and reduces complications. That is a rare metabolic disease — it does not transfer to using over-the-counter betaine for general 'methylation support' or heart health in healthy people.
Established benefit is specific to diagnosed inborn errors of homocysteine metabolism, under specialist care. Not a general-population indication.
Homocysteine lowering (with a lipid catch)
Mechanism
Betaine donates a methyl group to remethylate homocysteine back to methionine via betaine-homocysteine methyltransferase (BHMT), an alternative to the folate/B12 pathway. This reliably drops circulating homocysteine.
Betaine lowers homocysteine by ~1.2–1.3 µmol/L at 4–6 g/day — a solid, reproducible biomarker effect. The catch, proven across two analyses: at ≥4 g/day it also raises LDL (~10 mg/dL) and total cholesterol (~14 mg/dL). And critically, no trial has shown betaine reduces actual cardiovascular events — lowering homocysteine has repeatedly failed to cut heart attacks or strokes in the wider literature.
Biomarker benefit is real; clinical cardiovascular benefit is unproven and the lipid rise at homocysteine-lowering doses is a genuine downside. Most relevant for diagnosed hyperhomocysteinemia under clinician guidance — not for general 'heart health.'
Betaine and plasma homocysteine (meta-analysis)
positive · Meta-analysis
McRae, 2013, Journal of Chiropractic Medicinen=206Pooled 5 RCTs (n=206) of betaine in healthy adults. Betaine lowered plasma homocysteine by 1.23 µmol/L — roughly an 11.8% reduction from baseline. This is the cleanest, most reproducible betaine finding: it does what it says on the tin for the homocysteine biomarker.
A homocysteine reduction is a biomarker change, not a clinical outcome. No trial in this analysis measured heart attacks, strokes, or mortality. Lowering homocysteine has repeatedly failed to translate into cardiovascular event reduction across the broader B-vitamin literature.
Homocysteine-lowering nutrients and blood lipids
negative · RCT
Olthof et al., 2005, PLoS Medicinen=151The trade-off trial. 6 g/day betaine for 6 weeks lowered homocysteine but raised LDL cholesterol by 0.36 mmol/L (~14 mg/dL) and triacylglycerol by 0.14 mmol/L versus placebo. Effects appeared within 2 weeks. Lower doses (1.5–3 g/day) also nudged LDL up, though not significantly. The likely mechanism: betaine increases hepatic VLDL synthesis and export.
Healthy adults; the lipid rise is the central safety concern for betaine. Folic acid, by contrast, lowered homocysteine with no lipid penalty — a relevant alternative for homocysteine management.
Betaine and cardiovascular markers (meta-analysis)
mixed · Meta-analysis
Ashtary-Larky et al., 2021, Critical Reviews in Food Science and NutritionThe definitive risk-benefit summary. Betaine lowered homocysteine by 1.30 µmol/L but raised total cholesterol by 14.12 mg/dL and LDL by 10.26 mg/dL. No significant effect on triglycerides or blood pressure overall. The authors' own conclusion: a maximum of 4 g/day captures the homocysteine benefit without the lipid penalty seen at ≥4 g/day.
Confirms the Olthof finding at meta-analytic scale: the lipid harm is dose-dependent and clinically meaningful. This is why the 'performance' dose (2.5–3 g/day) sits deliberately below the homocysteine-lowering dose (4–6 g/day).
Strength, power and muscular endurance
Mechanism
As an organic osmolyte, betaine may support cellular hydration and protein synthesis, and as a methyl donor it may aid creatine synthesis. Proposed routes are plausible but not firmly established in humans.
Small resistance-training RCTs at 2.5 g/day show modest, inconsistent gains — more squat reps and some upper-body force/power in a few measures, but repeated null findings on vertical jump and Wingate power. The signal is real but narrow and lower-body-weighted, and several trials are industry-supported.
Most evidence is in young resistance-trained men at 2.5 g/day. Effects are modest and endpoint-selective. Not a proven ergogenic across the board.
Betaine for power performance and fatigue
mixed · RCT
Hoffman et al., 2009, Journal of the International Society of Sports Nutritionn=1214 days of 2.5 g/day betaine increased the number of squat repetitions performed and helped maintain power output across a set. But bench-press power, vertical jump, and Wingate anaerobic power did not differ from placebo. A signal in lower-body muscular endurance, not a broad ergogenic effect.
n=12, 14 days, crossover. Selective endpoint improvement (squat reps but not jump or Wingate) limits how strongly this can be read.
Ergogenic effects of betaine on strength and power
mixed · RCT
Lee et al., 2010, Journal of the International Society of Sports Nutritionn=1214 days of 2.5 g/day betaine increased bench-throw power and isometric bench force versus pre-supplementation, and increased squat reps on days 7–8. No effect on vertical jump power or Wingate anaerobic power. Effects clustered in 'selected' upper-body measures.
n=12. Some gains were within-group (vs pre-supplementation) rather than clean between-group differences, and several endpoints were null. A modest, inconsistent ergogenic picture.
Betaine on body composition and performance
positive · RCT
Cholewa et al., 2013, Journal of the International Society of Sports Nutritionn=236 weeks of 2.5 g/day betaine alongside periodized training improved body composition, increased arm size, increased bench-press work capacity, and blunted the rise in urinary homocysteine thiolactone. Power tended to improve (p=0.07) but strength did not.
Small (n=23, 11 on betaine), single training program. The most-cited 'betaine builds muscle' trial — but body-composition findings have not survived meta-analysis (Ashtary-Larky 2022 body-composition review).
Body composition (fat loss / muscle gain)
Mechanism
Proposed osmolyte and methyl-donor effects on lean tissue accretion. Mechanistically speculative for body composition specifically.
One trial (Cholewa 2013) reported improved body composition and arm size — but the 2022 meta-analysis found no significant effect on body weight, fat mass, or fat-free mass when the randomized evidence is pooled. The literature is conflicting (a 2019 meta did find fat-mass reduction), so the honest verdict is 'not established,' not 'proven.'
The 'betaine for recomposition' marketing claim is not supported by pooled trial data. Treat body-composition benefit as unproven.
Betaine on body composition and performance
positive · RCT
Cholewa et al., 2013, Journal of the International Society of Sports Nutritionn=236 weeks of 2.5 g/day betaine alongside periodized training improved body composition, increased arm size, increased bench-press work capacity, and blunted the rise in urinary homocysteine thiolactone. Power tended to improve (p=0.07) but strength did not.
Small (n=23, 11 on betaine), single training program. The most-cited 'betaine builds muscle' trial — but body-composition findings have not survived meta-analysis (Ashtary-Larky 2022 body-composition review).
Betaine fails to improve body composition (meta-analysis)
Null · Meta-analysis
Ashtary-Larky et al., 2022, British Journal of NutritionPooling the randomized evidence, betaine supplementation did not significantly improve body weight, fat mass, fat-free mass, or body fat percentage. The single-trial 'betaine recomposition' claim (Cholewa 2013) does not replicate at meta-analytic scale.
Directly contradicts the popular 'betaine for muscle gain and fat loss' marketing. The honest read: body-composition benefit is not established. (Note: an earlier 2019 meta-analysis reported fat-mass reduction, so the literature is genuinely conflicting — this is not a clean win for either side.)
Fatty liver (NAFLD/NASH)
Mechanism
Betaine supports hepatic methylation and was hypothesized to reduce liver fat and the second-hit oxidative injury in steatohepatitis — a story strongly supported in rodent models.
The one rigorous human RCT (Abdelmalek 2009) gave 20 g/day for 12 months to biopsy-proven NASH patients and failed its primary histologic endpoint. Strong animal data did not translate. There is no human evidence supporting betaine for fatty liver at supplement doses.
Negative human trial despite a far-higher-than-supplement dose. Do not use betaine to treat fatty liver.
Betaine for nonalcoholic fatty liver disease
negative · RCT
Abdelmalek et al., 2009, Hepatologyn=5555 patients with biopsy-proven NASH took 20 g/day betaine or placebo for a full year, with repeat liver biopsy. Betaine did not significantly improve the histologic steatosis score versus placebo on the primary endpoint, and failed to lower S-adenosylhomocysteine. Despite strong animal data for betaine in fatty liver, the human trial was negative.
Used a very high dose (20 g/day — far above any supplement dose) for 12 months and still failed its primary histologic endpoint. The clearest example of betaine's animal-to-human translation gap.
2 forms of TMG (Trimethylglycine) compared
Betaine anhydrous (TMG / trimethylglycine)
Well absorbed; rapidly raises plasma betaine
Best forHomocysteine lowering (4–6 g/day) and exercise performance (2.5–3 g/day)This is the form in essentially all the performance and homocysteine trials, and the form in prescription Cystadane®. 'TMG' and 'trimethylglycine' on a label mean the same molecule. Performance dosing (2.5–3 g/day) is deliberately kept below the homocysteine-lowering dose because the lipid-raising effect kicks in at ≥4 g/day.
muscle2500–3000 mgheart4000–6000 mgBetaine hydrochloride (Betaine HCl)
Releases hydrochloric acid in the stomach
Best forA digestive-acid product — NOT a TMG substituteA completely different use case. Betaine HCl is marketed to raise stomach acidity in suspected low-acid digestion; it delivers a small amount of betaine plus hydrochloric acid. It is NOT interchangeable with betaine anhydrous for homocysteine or performance, and the HCl load can irritate the stomach or worsen reflux. If a product lists 'betaine HCl,' it is not the TMG studied in the performance and homocysteine trials.
Are you deficient? Symptoms, risk groups, lab tests
Betaine is not an essential nutrient and has no RDA or upper limit. The body synthesizes it from choline, and average US dietary intake is roughly 100–300 mg/day (most sources cite ~150–200 mg/day), far below supplemental doses. Wheat bran, spinach, beets, and quinoa are the richest food sources. There is no clinically defined betaine-deficiency syndrome in otherwise healthy people.
Common symptoms
- No defined betaine-deficiency syndrome in healthy adults
- Low betaine status is mainly relevant as a contributor to elevated homocysteine
- Choline deficiency (betaine's precursor) can contribute to fatty liver, but that is a choline issue, not a betaine one
Who is at risk
Adults with elevated homocysteine (hyperhomocysteinemia)
When the folate/B12 remethylation pathway is impaired or overwhelmed, the betaine-BHMT pathway becomes more important for clearing homocysteine.
People with inherited homocystinuria
Inborn errors such as CBS deficiency cause dangerously high homocysteine; prescription betaine is part of standard management under specialist care.
Lab markers
Plasma total homocysteine
This is the marker betaine reliably moves. A lower homocysteine is a biomarker improvement — it has not been shown to translate into fewer cardiovascular events. Interpret alongside a lipid panel, because betaine at ≥4 g/day raises LDL.
- Optimal
- <10 µmol/L
- Moderate hyperhomocysteinemia
- 15–30 µmol/L
Side effects and drug interactions
Side effects
Raised LDL and total cholesterol
Common · Significant at ≥4 g/day; smaller, non-significant rises at 1.5–3 g/day
The signature betaine concern. At ≥4 g/day, betaine raises LDL by ~10 mg/dL and total cholesterol by ~14 mg/dL, likely via increased hepatic VLDL synthesis and export. This is precisely the dose range used to lower homocysteine — so the homocysteine benefit comes bundled with a lipid penalty.
Gastrointestinal upset
Uncommon · More common above 4 g/day
Nausea, bloating, diarrhea, and abdominal discomfort, particularly at the higher (4–6 g/day and above) doses and on an empty stomach.
Body / breath odor (trimethylaminuria-type)
Uncommon · Higher gram-level doses
High betaine intake can increase production of trimethylamine, producing a fishy body or breath odor in susceptible individuals.
Stomach irritation (Betaine HCl specifically)
Uncommon
The hydrochloride form delivers hydrochloric acid and can irritate the gastric lining or worsen reflux. This is a Betaine HCl issue, not a betaine anhydrous issue.
Worse with:betaine hcl
Drug interactions
Combined-effect risk
statinsezetimibeother lipid-lowering therapyBetaine at ≥4 g/day raises LDL and total cholesterol, working against the goal of lipid-lowering therapy.
If you take betaine at homocysteine-lowering doses, monitor your lipid panel. People on statins for cardiovascular risk should be aware betaine can blunt their lipid targets.
Other
folic acidvitamin B6vitamin B12These nutrients lower homocysteine through the folate/B12 remethylation pathway — without raising lipids (Olthof 2005). They are a relevant alternative or adjunct for homocysteine management.
For homocysteine lowering, folate/B12/B6 achieve the biomarker effect without the lipid penalty. Consider these before high-dose betaine for that purpose.
Other critical caveats
- Betaine anhydrous (TMG) and Betaine HCl are not the same product. TMG is the methyl donor studied for homocysteine and athletic performance. Betaine HCl is a stomach-acid product sold for digestion and is not interchangeable. Check which one a label lists.
- The lipid trade-off is the headline safety issue: at the 4–6 g/day doses that lower homocysteine, betaine raises LDL (~10 mg/dL) and total cholesterol (~14 mg/dL) per two separate analyses (Olthof 2005, Ashtary-Larky 2021). Performance dosing (2.5–3 g/day) stays below this threshold deliberately.
- Lowering homocysteine is not the same as preventing heart disease. Betaine reliably drops the homocysteine biomarker, but no trial has shown it reduces heart attacks, strokes, or death — and across the broader literature, homocysteine-lowering has repeatedly failed to cut cardiovascular events.
- The fatty-liver case is built on animal data. The one rigorous human RCT (Abdelmalek 2009) used 20 g/day for a year in biopsy-proven NASH and failed its primary endpoint. Do not use betaine to treat fatty liver.
- The body-composition / 'muscle building' claim is not supported by pooled trials. A 2022 meta-analysis found no significant effect on fat mass or fat-free mass; the literature is conflicting at best.
Frequently asked
Is betaine (TMG) the same as Betaine HCl?
No. Betaine anhydrous (TMG / trimethylglycine) is the methyl donor studied for lowering homocysteine and for exercise performance — it's also the prescription drug Cystadane® for homocystinuria. Betaine HCl is a different product: it's marketed as a digestive aid to add stomach acid, and it delivers hydrochloric acid that can irritate the stomach. They are not interchangeable. If you want the studied TMG effects, buy betaine anhydrous, not betaine HCl.Does betaine lower homocysteine?
Yes — this is its most solid effect. At 4–6 g/day, betaine lowers plasma homocysteine by about 1.2–1.3 µmol/L (~12%). The catch: at those same doses it raises LDL cholesterol by ~10 mg/dL and total cholesterol by ~14 mg/dL. And lowering homocysteine is a biomarker change, not a proven reduction in heart attacks or strokes. If your goal is homocysteine specifically, folate, B12, and B6 lower it without raising your lipids.How much betaine should I take, and for what?
For exercise performance, the trial dose is 2.5–3 g/day — deliberately below the threshold where lipids rise. For homocysteine lowering, trials use 4–6 g/day, but at that dose you accept an LDL and total-cholesterol increase. Average dietary intake is only ~150–200 mg/day, so supplements are well above food levels. Don't exceed 4 g/day casually if you care about your cholesterol.Will betaine build muscle or help me lose fat?
The evidence is weak and conflicting. Small resistance-training trials at 2.5 g/day show modest, inconsistent gains — more squat reps and a couple of upper-body power measures, but null results on jump and anaerobic power. One trial reported body-composition improvements, but a 2022 meta-analysis found no significant effect on fat mass or fat-free mass when trials are pooled. Treat 'betaine for recomposition' as unproven.Is betaine good for fatty liver?
Not based on human evidence. Despite strong results in animal models, the one rigorous human RCT gave 20 g/day for 12 months to people with biopsy-proven NASH and failed its primary histologic endpoint. There's no human support for using betaine to treat fatty liver.
References
- 01McRae, 2013 — Betaine and plasma homocysteine meta-analysis (J Chiropr Med)
- 02Olthof et al., 2005 — Betaine, homocysteine and blood lipids (PLoS Medicine)
- 03Ashtary-Larky et al., 2021 — Betaine and cardiovascular markers meta-analysis (Crit Rev Food Sci Nutr)
- 04Abdelmalek et al., 2009 — Betaine for NAFLD/NASH RCT (Hepatology)
- 05Hoffman et al., 2009 — Betaine power performance RCT (JISSN)
- 06Examine.com — Betaine (TMG / Trimethylglycine)
- 07Cystadane (betaine anhydrous) — FDA prescribing information for homocystinuria
Last reviewed2026-05-24