Most research on TMG (trimethylglycine, also called betaine) has used daily doses between 1.5 and 6 grams, with the specific amount depending on the goal. For lowering homocysteine, studies show measurable effects starting at 1.5 grams per day, while athletic performance trials typically use 2.5 grams. The supplement is generally well tolerated, but it comes with a noteworthy trade-off involving cholesterol that anyone considering it should understand before starting.
What TMG Actually Does
TMG is a methyl donor, meaning it hands off a chemical group called a methyl group to other molecules in your body. Its best-understood job is converting homocysteine, an amino acid linked to cardiovascular risk when elevated, back into methionine. An enzyme called BHMT (betaine-homocysteine methyltransferase) drives this reaction, and TMG is the molecule that supplies the needed methyl group.1PubMed Central. Human betaine-homocysteine methyltransferase (BHMT) and BHMT2: common gene sequence variation and functional characterization This pathway operates primarily in the liver and kidneys. When TMG donates its methyl group, it also supports the production of S-adenosylmethionine (SAM), a compound involved in hundreds of methylation reactions throughout your body.
Dosage for Lowering Homocysteine
The most studied use of TMG supplements is bringing down elevated homocysteine. A six-week trial in healthy men and women tested three doses head to head against placebo. Daily doses of 1.5 grams reduced fasting homocysteine by about 12%, 3 grams reduced it by about 15%, and 6 grams reduced it by roughly 20%.2PubMed. Low dose betaine supplementation leads to immediate and long term lowering of plasma homocysteine in healthy men and women The effect was dose-dependent but showed diminishing returns: tripling the dose from 1.5 to 6 grams did not triple the benefit.
What stood out was TMG’s ability to blunt the spike in homocysteine that follows a protein-heavy meal. After six weeks, that post-meal spike was dampened by 23% at 1.5 grams per day, 30% at 3 grams, and 40% at 6 grams.2PubMed. Low dose betaine supplementation leads to immediate and long term lowering of plasma homocysteine in healthy men and women A separate trial using 6 grams daily for six weeks found a similar fasting reduction and confirmed that TMG was particularly effective at suppressing post-meal homocysteine rises, a scenario where folic acid, the other common homocysteine-lowering supplement, showed no benefit.3PubMed. Betaine supplementation lowers plasma homocysteine in healthy men and women
A review of the epidemiological literature confirms the general range, noting that supplementation between 1.5 and 6 grams per day reduces fasting homocysteine in both healthy people and those with elevated levels.4PubMed Central. Dietary Choline and Betaine Intakes and Risk of Cardiovascular Diseases: Review of Epidemiological Evidence For most people looking to manage homocysteine, the 1.5 to 3 gram range captures most of the benefit with fewer potential downsides, which we will get to shortly.
Dosage for Exercise and Body Composition
Athletic performance studies have almost uniformly used 2.5 grams of TMG per day, typically split into two doses. The evidence here is genuinely mixed, and it would be misleading to present TMG as a proven performance booster. A systematic review covering seven studies found that only two reported increases in strength or power after TMG supplementation, while the remaining five showed no change.5PubMed. Effects of Betaine Supplementation on Muscle Strength and Power: A Systematic Review
That said, some individual trials have reported interesting secondary findings. One study in resistance-trained men found that 2.5 grams per day improved body composition: body fat percentage, fat mass, and lean body mass all moved in the right direction compared to placebo. Arm muscle size increased, and bench press training volume improved. However, actual one-rep-max strength on the squat and bench press did not differ between groups.6PubMed Central. Effects of betaine on body composition, performance, and homocysteine thiolactone Another trial found that TMG supplementation led to roughly a 6.5% increase in total bench press volume (more reps at the same weight), but no improvements in other performance measures.7PubMed. The effects of chronic betaine supplementation on exercise performance, skeletal muscle oxygen saturation and associated biochemical parameters in resistance trained men
The honest summary is that TMG at 2.5 grams daily might provide small improvements in training volume and body composition for people doing resistance training, but the evidence for direct strength or power gains is weak. If you are looking for a reliable ergogenic supplement, the data for creatine is far stronger. TMG is more of an “interesting maybe” in the fitness space.
How Much You Get from Food
Your body gets TMG from two routes: you eat it directly, or your body makes it by oxidizing choline. Dietary sources include wheat bran, quinoa, beets, and spinach. But the typical Western diet delivers only about 131 milligrams of betaine per day on average, with cereal foods accounting for roughly 60 to 67% of that total.8PubMed. Cereal foods are the major source of betaine in the Western diet–analysis of betaine and free choline in cereal foods and updated assessments of betaine intake That is well below the 1,500 milligrams that represents the lowest dose used in intervention studies.
So can you close the gap with food? A crossover study had healthy men consume either a betaine-rich diet providing about 800 milligrams per day or a supplement of 1 gram daily (500 milligrams twice) for two weeks. Both approaches raised circulating betaine levels by similar amounts and both reduced post-meal homocysteine spikes.9Nutrition, Metabolism & Cardiovascular Diseases. Dietary and supplementary betaine: effects on betaine and homocysteine concentrations in males In another trial, a single high-betaine meal raised plasma betaine significantly within an hour, though a supplement produced a higher peak faster.10The American Journal of Clinical Nutrition. Dietary and supplementary betaine: acute effects on plasma betaine and homocysteine concentrations under standard and postmethionine load conditions in healthy male subjects
The practical takeaway: food-based betaine can raise your levels meaningfully, but getting to the 1.5+ gram range that clinical trials have used for homocysteine lowering would require either a very deliberately constructed diet or supplementation. Most people who take TMG for a specific health goal end up using a supplement.
The Cholesterol Trade-Off
This is the side effect that deserves the most attention, and it is often glossed over in supplement marketing. A series of four randomized, placebo-controlled trials found that 6 grams of TMG per day for six weeks raised LDL (“bad”) cholesterol by 0.36 mmol/L and triglycerides by 0.14 mmol/L compared to placebo. The ratio of total cholesterol to HDL cholesterol also increased. HDL (“good”) cholesterol was not affected.11PubMed Central. Effect of homocysteine-lowering nutrients on blood lipids: results from four randomised, placebo-controlled studies in healthy humans The LDL increase was already evident after two weeks, and doses below 6 grams also raised LDL, though those increases did not reach statistical significance in the studies analyzed.11PubMed Central. Effect of homocysteine-lowering nutrients on blood lipids: results from four randomised, placebo-controlled studies in healthy humans
This creates an awkward dilemma. One reason people take TMG is to lower homocysteine, which is itself considered a cardiovascular risk marker. But the supplement simultaneously nudges LDL cholesterol upward, another cardiovascular risk marker. Whether the homocysteine reduction outweighs the LDL increase for any given person depends on their baseline lipid profile, their cardiovascular risk, and what else they are doing to manage cholesterol. If your LDL is already elevated, adding 6 grams of TMG daily without monitoring your lipids would be unwise. The lower-dose range (1.5 to 3 grams) may carry less lipid impact, but the evidence is not robust enough to be certain, and periodic bloodwork is a reasonable precaution at any dose.
Other Side Effects and Tolerability
Beyond the lipid concern, TMG is generally well tolerated at doses used in research. The most commonly reported complaints are gastrointestinal in nature: nausea, stomach upset, and diarrhea, typically at higher doses. Some people notice a fishy body odor, which results from a metabolite called trimethylamine. This side effect is dose-dependent and more common at 6 grams per day than at lower doses.
No formal tolerable upper intake level has been established by major regulatory bodies for betaine as a supplement. The doses used in clinical trials (up to 6 grams per day for six weeks) have not produced serious adverse events in healthy adults. For reference, the medical form of betaine (brand name Cystadane) is prescribed at much higher doses, sometimes 6 to 20 grams per day, for people with the rare metabolic disorder homocystinuria. These patients are monitored closely, and the risk-benefit calculation is very different from someone taking a supplement for general health.
How Your Body Absorbs TMG
TMG is absorbed quickly after oral intake. A pharmacokinetic study in healthy subjects found that betaine reaches peak blood concentrations in under an hour, with an absorption half-life of about 17 minutes. The elimination half-life averaged around 14 hours, meaning levels stay elevated for a good portion of the day after a single dose.12PubMed Central. Pharmacokinetics of oral betaine in healthy subjects and patients with homocystinuria Both absorption and elimination are dose-dependent: higher doses produce proportionally higher blood levels, but they also take longer to clear.13PubMed. Orally administered betaine has an acute and dose-dependent effect on serum betaine and plasma homocysteine concentrations in healthy humans
Because blood levels stay elevated for many hours, splitting your daily dose into two servings (morning and evening) is common practice but not strictly necessary for the homocysteine-lowering effect. The trials that demonstrated efficacy used both single-dose and split-dose protocols. If you experience GI discomfort from taking the full amount at once, splitting the dose often helps.
TMG and Liver Health
TMG’s role in the liver extends beyond homocysteine metabolism. Because the liver is the primary site of betaine-homocysteine methyltransferase activity, TMG supplementation directly influences hepatic methylation and fat metabolism. A comprehensive review notes that betaine helps prevent metabolic-associated fatty liver disease and slows its progression.14PubMed Central. Beneficial Effects of Betaine: A Comprehensive Review
Animal data adds mechanistic detail. In mice fed a moderately high-fat diet, betaine treatment reduced fasting glucose, insulin, triglycerides, and hepatic fat. It both prevented and treated fatty liver in these models, with improvements in insulin resistance accompanying the reduction in liver fat.15PubMed Central. Betaine improves nonalcoholic fatty liver and associated hepatic insulin resistance: a potential mechanism for hepatoprotection by betaine An earlier rat study found that dietary betaine increased SAM levels in the liver and protected against alcohol-induced fatty liver at sufficient doses.16PubMed Central. S-adenosylmethionine generation and prevention of alcoholic fatty liver by betaine
Human data on TMG for fatty liver is still limited. A prospective study assessed TMG in patients diagnosed with non-alcoholic fatty liver disease and found results suggesting a role for betaine in treatment, though the study noted the need for larger trials to confirm the findings.17International Journal of Health Sciences and Research. Prospective study on safety and efficacy of trimethylglycine in patients with non-alcoholic fatty liver disease with or without fibrosis The liver health angle is promising but not yet strong enough to recommend TMG specifically for fatty liver outside of a clinical setting.
Who Might Benefit Most
TMG supplementation makes the most straightforward case for people with confirmed elevated homocysteine, particularly those who have not responded fully to folate and B12 supplementation. TMG works through a different enzymatic pathway than folate, so the two approaches are complementary rather than redundant. People with MTHFR gene variants, which can impair the folate-dependent pathway for recycling homocysteine, sometimes find TMG especially useful because it provides an alternative route for bringing homocysteine down. You would need a genetic test or a blood test showing persistently elevated homocysteine despite adequate folate intake to know if this applies to you.
For athletes and fitness enthusiasts, the 2.5-gram dose is low-risk and inexpensive, but expectations should be calibrated to the evidence. Small improvements in training volume are plausible, meaningful changes in maximal strength or power are not well supported. People who are already taking creatine might view TMG as a complementary supplement, since TMG spares methyl groups that would otherwise be consumed during creatine synthesis in the body.
Practical Dosing Guidance
Pulling the research together, here is how the dosage landscape breaks down by purpose:
- General methylation support: 500 mg to 1.5 g per day. This range is close to what a betaine-rich diet might provide and sits below the threshold where lipid effects have been observed in trials.
- Homocysteine lowering: 1.5 to 3 g per day. This range captures most of the homocysteine benefit with a potentially smaller impact on LDL than 6 grams.
- Exercise performance: 2.5 g per day, based on the dose used in nearly all athletic performance trials.
- Higher therapeutic doses: 6 g per day has been used in research and shows the strongest homocysteine reduction but also the clearest increase in LDL cholesterol. Lipid monitoring is advisable at this level.
TMG powder dissolves easily in water and has a mildly sweet taste, which makes it one of the more palatable supplements to take in bulk-powder form. Capsules typically contain 500 mg to 1 gram each. Taking it with food may reduce the chance of stomach discomfort, though the pharmacokinetic data suggests absorption is rapid regardless of meal timing.
Because TMG can raise LDL cholesterol and the research base on long-term supplementation in healthy people is still limited, checking a lipid panel a few weeks after starting supplementation is a reasonable step, especially if you are using doses above 1.5 grams per day. If your LDL rises meaningfully, reducing the dose or discontinuing the supplement is a simple fix, as the effect appears to be reversible based on the trial data.
TMG, Choline, and the Methyl Group Economy
TMG is sometimes confused with choline, and the relationship between them matters for dosing decisions. Your body can convert choline into TMG through a two-step oxidation process in the liver. So choline is, in a sense, a precursor to TMG. But the conversion is not instantaneous or complete, and the two molecules have distinct roles. Choline is also needed for making acetylcholine (a neurotransmitter) and phosphatidylcholine (a component of cell membranes), so not all of the choline you consume ends up as TMG.
This is relevant because some people take both choline and TMG supplements, and others wonder if choline alone is sufficient. If your goal is specifically to lower homocysteine, TMG is the more direct route since it skips the conversion step. If your goal is broader support for brain health, cell membrane integrity, and methylation, choline covers more ground but delivers less TMG per milligram. The two supplements are not interchangeable, even though they share a metabolic connection.
People who take high-dose creatine may have an additional reason to consider TMG. The body’s synthesis of creatine consumes a large share of available methyl groups. By supplying extra methyl groups through TMG, you could theoretically free up more of your body’s methylation capacity for other reactions. This is a reasonable biochemical argument, though direct clinical evidence quantifying the benefit of combining creatine with TMG in humans remains limited.