Trimethylglycine, a methyl donor found in beetroot, wheat bran and spinach. It converts homocysteine back to methionine and acts as an osmolyte in kidney and liver cells.
Betaine has one firmly established effect and one contested one. The established effect is homocysteine lowering: it is dose-dependent, replicated, recognised by EFSA at 1.5 g/day and used pharmacologically at much higher doses in inherited homocystinuria, where it is an approved drug. The contested one is performance — trials of 2.5 g/day in resistance-trained people report improvements in power and body composition in some studies and nothing in others. The important and rarely mentioned catch is that the doses used to lower homocysteine raise total and LDL cholesterol, which is an awkward trade for a compound sold on cardiovascular reasoning.
Grams of anhydrous betaine — distinct from betaine hydrochloride, which is a different product used to acidify the stomach — a product without this marker may not resemble what was studied.
Also known as
Betaine, TMG, Trimethylglycine, Glycine betaine
Regulation: Approved as a prescription drug for homocystinuria. Sold as a dietary supplement with no pre-market efficacy review. EFSA authorised a claim that betaine contributes to normal homocysteine metabolism at 1.5 g/day, while explicitly noting that intakes above 4 g/day may significantly raise blood cholesterol.
What the research used
The amounts, forms and durations published trials of Betaine anhydrous (TMG) actually administered.
These are the amounts published trials administered — not a recommendation, and not a dose to copy. Trial participants were screened, supervised and given a characterised preparation. What is in a retail bottle is frequently not what was studied, and the amount that suits one person is not general advice.
Studied for Homocysteine lowering
1.5–6 g
Moderate
Betaine anhydrous daily · 6–12 weeks
Dose-dependent and well replicated. EFSA authorised a claim at 1.5 g/day and simultaneously warned that intakes above 4 g/day may significantly raise blood cholesterol, which is the trade-off nobody advertises.
Studied for Strength and power in resistance training
2.5 g
Limited
Daily, often divided · 6–15 weeks
Nearly all performance trials use 2.5 g/day. Results are split between modest improvements and no effect, and the trials are small.
This is general information about food, not medical advice. It cannot diagnose, treat or replace guidance from a clinician who knows your history.
When it was taken
Each window says whether a trial compared it against an alternative, or whether it is convention and pharmacology. Most timing advice is the second kind.
None of the timings below were directly compared in a trial. They reflect how the research happened to dose, or what the pharmacology implies — which is not the same as a timing being better.
🕐Any time
Not enough
No timing comparison has been published. Trials divide the dose for tolerability rather than for any demonstrated advantage.
Timing was not directly compared. This reflects convention or how the compound behaves in the body, not a trial showing this window works better.
The evidence in depth
Best supported: Limited
What each association actually rests on, and the papers behind it. A rating describes the state of the research, not how promising the supplement sounds. How we rate evidence.
Betaine lowers homocysteine dose-dependently, which is a well-established biochemical effect. Homocysteine lowering has not translated into reduced cardiovascular events in the large trials that tested it with B vitamins, and betaine simultaneously raises LDL and total cholesterol at higher doses — so the surrogate improves while another surrogate worsens.
What may be going on: Betaine-homocysteine methyltransferase transfers a methyl group from betaine to homocysteine, regenerating methionine.
Limited evidence. Early human work, or mostly lab and animal research.
Trials of 2.5 g/day in trained people report modest improvements in power output, repetitions and body composition in some studies and no difference in others. Meta-analyses describe the evidence as inconsistent and the trials as small.
Limited evidence. Early human work, or mostly lab and animal research.
Betaine has been studied in non-alcoholic fatty liver disease on the basis of its role in methyl metabolism, with small trials producing inconsistent results. There is not enough evidence to support a liver claim.
Not enough evidence. Not enough human research to say anything useful yet.
Deep research mode adds each paper’s own conclusion and stated limitations.
Things to know
Interactions, contraindications and dose limits, most serious first. Concentrated extracts interact with medication in ways the whole plant does not, so this section carries more weight here than it does on a food page.
Too much
Raises LDL and total cholesterol at higher doses
Controlled trials show betaine raises total and LDL cholesterol dose-dependently, and EFSA attached an explicit warning to its authorised claim that intakes above 4 g/day may significantly increase blood cholesterol. Taking it to improve a cardiovascular surrogate while worsening a better-validated one is a poor trade.
Worth knowing
Not the same as betaine hydrochloride
Betaine anhydrous is a methyl donor. Betaine hydrochloride is used to acidify the stomach and carries entirely different cautions. The names are close enough that products are regularly confused.
Worth knowing
Cerebral oedema at pharmacological doses
Cases of cerebral oedema have been reported in patients treated with high-dose betaine for homocystinuria, particularly where methionine rose steeply. This belongs to supervised pharmacological use rather than supplement doses, but it is why that use is monitored.
Too much
Body odour and digestive upset
Betaine is metabolised in part to trimethylamine, and a fishy body odour is reported at higher doses. Nausea and diarrhoea occur at multi-gram intakes.
In the food catalogue
The whole-food form, where one exists. The evidence for a concentrated extract rarely transfers to the food, or the other way round — these are cross-links, not equivalents.