TMG (trimethylglycine), also called betaine, is a naturally occurring compound used primarily to lower homocysteine levels, support liver health, and improve exercise performance. It works by donating a chemical unit called a methyl group to reactions throughout the body, making it a key player in a metabolic process that influences everything from heart health to how your cells repair DNA. You’ll find TMG sold as a standalone supplement (often labeled “betaine anhydrous”) and naturally present in foods like beets, wheat bran, and spinach.
How TMG Works in the Body
TMG has two core functions: it acts as a methyl donor and as an osmolyte, meaning it helps cells maintain their water balance under stress. The methyl donor role is the one that drives most of its health benefits.
Here’s the simplified version. Your body constantly produces a byproduct called homocysteine during normal protein metabolism. High homocysteine is linked to cardiovascular problems and liver damage, so the body needs to recycle it back into a useful amino acid called methionine. TMG does this directly: it hands off one of its three methyl groups to homocysteine, converting it into methionine. That methionine then gets used to make SAMe (S-adenosylmethionine), a compound involved in over 100 chemical reactions in the body, including the synthesis of neurotransmitters, the repair of DNA, and the processing of fats in the liver.
This pathway normally relies on folate (vitamin B9) and vitamin B12 as cofactors. TMG provides an alternate route to the same destination, which is why it’s sometimes used alongside B vitamins or as a substitute when folate metabolism is impaired.
Lowering Homocysteine
The most well-documented use of TMG is reducing plasma homocysteine levels. Elevated homocysteine is an independent risk factor for cardiovascular disease, and TMG supplementation at doses of 4 to 6 grams per day lowers it by roughly 12% in healthy adults. Some studies show reductions ranging from 5% to 20% depending on the dose and baseline levels. This effect is particularly relevant for people with a genetic condition called homocystinuria, where the body cannot properly break down homocysteine, though the supplement also benefits those with mildly elevated levels from diet or lifestyle factors.
Liver Protection
TMG plays a significant protective role in the liver, where the enzyme that uses it to recycle homocysteine is most active. Chronic alcohol consumption depletes SAMe in the liver while allowing homocysteine to build up, creating a toxic imbalance. TMG restores this balance by feeding directly into the recycling pathway, replenishing SAMe levels and maintaining normal methylation activity in liver cells.
This mechanism is relevant beyond alcohol-related damage. Research identifies TMG as a preventive agent for metabolic-associated fatty liver disease (sometimes called NAFLD), where fat accumulates in the liver due to diet and metabolic dysfunction. By keeping the methylation cycle running smoothly, TMG helps the liver process and export fats rather than storing them. The protective effects are primarily tied to its ability to remove homocysteine and keep the ratio of SAMe to its byproduct (SAH) in a healthy range.
Exercise and Body Composition
Betaine anhydrous has become a popular sports supplement, typically dosed at 2.5 grams per day. A six-week trial comparing betaine supplementation to placebo during a structured resistance training program found several notable results:
- Body composition: The betaine group significantly reduced body fat percentage and fat mass while increasing lean body mass. The placebo group saw no comparable changes.
- Arm size: Upper arm muscle cross-sectional area increased in the betaine group but not in the placebo group.
- Work capacity: Bench press training volume improved by about 8% more than placebo after the first training block, and roughly 5% more by the third block.
- Power: Vertical jump power showed a trend toward improvement with betaine, though the result did not reach full statistical significance.
One important nuance: betaine did not increase one-rep max strength on the bench press or squat. The benefits appear to be more about training volume (how much total work you can do in a session) and body composition than raw strength. For people doing high-volume resistance training, this could translate to better long-term muscle growth simply by enabling more productive workouts.
Mood and Brain Health
Because TMG feeds into SAMe production, it has an indirect relationship with mental health. SAMe is involved in synthesizing neurotransmitters like serotonin, dopamine, and norepinephrine. Lower SAMe levels are associated with decreased production of these mood-regulating chemicals and a higher risk of depression. TMG helps keep the pipeline flowing by ensuring enough methionine is available for SAMe synthesis.
TMG is sometimes recommended as an alternative when someone cannot tolerate folinic acid, the standard supplement used to support methylation in clinical settings. Folate and B12 remain the primary nutritional tools for maintaining healthy methylation in the brain, but TMG offers a parallel pathway to the same goal. This makes it a useful add-on for people with certain genetic variations (like MTHFR polymorphisms) that reduce their ability to process folate efficiently.
Food Sources of TMG
You don’t need a supplement to get TMG in your diet. According to USDA analysis of 241 foods, wheat bran and wheat germ contain the highest concentrations at over 1,000 mg per 100 grams. Baked products made from wheat flour provide 33 to 226 mg per 100 grams. Spinach, beets, and seafood (both shellfish and finfish) are also good sources. On the low end, foods like ground beef, beer, and iced tea contain fewer than 6 mg per 100 grams.
That said, dietary intake alone rarely reaches the 2.5 to 6 gram range used in clinical studies, which is why supplementation is common for people targeting specific health outcomes.
Typical Doses
Dosing depends on the goal. For exercise performance and body composition, most research uses 2.5 grams per day, usually split into two doses. For homocysteine reduction, clinical studies use 4 to 6 grams per day. TMG supplements are generally taken with meals, and the compound is water-soluble, so it absorbs readily.
The FDA lists betaine as GRAS (Generally Recognized as Safe) as a food substance. There is no formally established tolerable upper intake level, but doses in the 2.5 to 6 gram range have been used in studies without serious adverse effects. The most commonly reported side effects are mild gastrointestinal symptoms like nausea, bloating, or diarrhea, particularly at higher doses. TMG can also cause a fishy body odor in some people because of how the body metabolizes it. One thing worth noting: because TMG converts homocysteine into methionine, very high doses could theoretically raise methionine levels, so balance matters.
How TMG Relates to B Vitamins and Choline
TMG doesn’t work in isolation. It sits within a broader network of nutrients that all feed into the same methylation cycle. Folate, vitamin B12, vitamin B6, choline, and zinc all play roles as either methyl donors or cofactors in this system. Your body actually makes TMG from choline through a two-step oxidation process, which is why choline deficiency and TMG deficiency tend to produce overlapping problems, particularly in the liver.
Supplementing TMG can partially compensate for low folate or B12 status because it provides an alternative way to recycle homocysteine. But it cannot fully replace these vitamins, since they serve additional functions beyond methylation. The most effective approach for people concerned about methylation capacity is ensuring adequate intake of the full set of nutrients rather than relying on any single one.