Also known as: Trimethylglycine, TMG, Betaine anhydrous, Glycine betaine, Beet extract
Performance & PowerStrong evidence
A methyl donor derived from glycine, found in beetroot and wheat bran. Works through two unrelated routes — methylation and cellular hydration — and has a modest but reasonably consistent performance literature.
Typical dose
2500.0–2500.0 mg per day
Daily with food; timing not critical
What it is
Betaine, or trimethylglycine, is glycine with three methyl groups attached. It was first isolated from sugar beet, which gives it its name, and is also found in wheat bran, spinach, quinoa and shellfish.
It should not be confused with betaine hydrochloride, a different product used to increase stomach acidity. Supplements for performance use betaine anhydrous, and the two are not interchangeable despite the shared name.
Typical dietary intake is well below supplemental doses, sitting somewhere in the region of 100-400 mg daily depending on how much wholegrain and beetroot the diet contains. Supplements typically supply 2.5 g.
How it works
Betaine's first role is as a methyl donor. It donates a methyl group to homocysteine, converting it back to methionine, which both lowers homocysteine and supports the SAMe pool used throughout the body for methylation reactions, including creatine synthesis.
Its second role is entirely separate. Betaine is an osmolyte, accumulating inside cells and protecting them against osmotic and thermal stress by maintaining cell volume. This is the proposed basis for the performance effects, particularly under heat or dehydration.
These two mechanisms are unrelated, which is unusual, and it makes the ingredient harder to reason about than most. The methylation role is well established biochemically; the performance role is more contested.
What the evidence shows
Homocysteine lowering is well established and is the least contested part of the evidence base for betaine.
Performance research is more mixed but leans positive. Several trials have reported improvements in strength, power output and training volume in resistance-trained subjects, and meta-analyses have generally identified a small benefit, particularly for muscular endurance. Other trials have found nothing.
Body composition findings are inconsistent. There is also a relevant caveat: betaine supplementation can raise LDL cholesterol in some individuals, which is worth being aware of if yours is already being watched.
Dosing
The standard dose is 2.5 g daily, used with striking consistency across the performance literature. Some protocols split this into two 1.25 g servings.
Higher doses, 3-6 g, have been used in homocysteine research but offer no established performance advantage and increase the likelihood of the cholesterol effect noted below.
Timing does not appear to matter much, since the effects are cumulative rather than acute. Take it daily with food. Trials generally ran two to six weeks before measuring outcomes. Note that betaine and choline are metabolically linked, so a diet already high in choline may reduce the marginal benefit.
Plasma betaine peaks within 1-2 hours; effects accrue over weeks
Timing
Daily with food; timing not critical
Competition status
Permitted — not on the WADA Prohibited List
Category
Performance & Power
Safety and side effects
Generally well tolerated. Digestive effects including nausea, cramping and diarrhoea are the most common complaints, usually at higher doses. Some users report a distinctive body odour at high intakes.
The consideration worth flagging is lipids. Several trials have found that betaine supplementation raises total and LDL cholesterol in some individuals, an effect thought to relate to its influence on lipid metabolism. Anyone with existing cholesterol concerns should be aware of this and consider monitoring.
Betaine metabolism can also produce trimethylamine N-oxide, or TMAO, which has been discussed in relation to cardiovascular risk, though the clinical significance remains debated.
Who should avoid it
Take care if your cholesterol is being monitored, given reported effects on LDL. Speak to your doctor before use if you take regular medication or are under medical care. Not established for use in pregnancy or breastfeeding at supplemental doses. Do not confuse with betaine hydrochloride, which serves an entirely different purpose.
This entry is provided for information only. Food supplements should not be used as a substitute for a varied and balanced diet and a healthy lifestyle. Consult a qualified healthcare professional before use if you are pregnant, breastfeeding, taking medication or under medical supervision.
