Trimethylglycine (TMG), also called betaine, is a naturally occurring compound found in foods like beets, spinach, and wheat. It plays a genuine role in several important body processes, and doses up to 6 grams daily are considered safe for most adults. Whether it’s “good for you” depends on what you’re hoping it will do. The evidence is strong for some uses and weaker for others.
What TMG Does in Your Body
TMG’s main job is donating a molecular building block called a methyl group during a critical recycling process in your cells. Specifically, it helps convert homocysteine, a potentially harmful amino acid, back into methionine, a useful one. This matters because methionine goes on to produce SAM-e (S-adenosylmethionine), a compound your body uses for hundreds of reactions, from building neurotransmitters to repairing DNA to processing fats in the liver.
TMG also works as an osmolyte, meaning it helps cells maintain their water balance under stress. This is especially important in the kidneys, where cells in the inner medulla face a punishing environment of high salt and urea concentrations. Betaine accumulates inside these cells to keep them from shrinking or losing function. The same protective mechanism operates in liver cells and, to some extent, in the brain.
Homocysteine and Heart Health
High homocysteine is a well-established marker of cardiovascular risk, and TMG reliably lowers it. At doses of 4 grams per day or more, TMG is actually a cornerstone treatment for people with genetic conditions that cause dangerously high homocysteine levels, such as homocystinuria and certain MTHFR deficiencies.
Here’s the catch: lowering homocysteine hasn’t translated into fewer heart attacks or strokes in the general population. Several large clinical trials (HOPE-2, NORVIT, VITATOPS) used B vitamins to reduce homocysteine by 20 to 32 percent and found no meaningful reduction in heart attacks, coronary heart disease, or death from any cause. Current evidence does not support routine homocysteine-lowering for people without a diagnosed deficiency. TMG can bring homocysteine down, but that number dropping on a lab test doesn’t appear to protect your heart in the way researchers once hoped.
Liver Protection
The liver is where TMG’s benefits look most promising. A large body of research shows betaine has protective effects against multiple forms of liver disease, including non-alcoholic fatty liver disease (NAFLD), alcohol-related liver damage, drug-induced liver injury, and even liver fibrosis. The mechanisms are broad: TMG reduces fat accumulation in liver cells by promoting fatty acid breakdown, dials down inflammatory signaling, eases a type of cellular stress called endoplasmic reticulum stress, and improves insulin resistance.
Much of the fat-clearing effect traces back to that same methyl-donor function. By converting homocysteine to methionine in the liver, TMG supports the production of compounds the liver needs to package and export fat rather than storing it. If you’re concerned about liver health, particularly fatty liver, TMG is one of the more evidence-backed supplements available.
Athletic Performance
Betaine has become popular in pre-workout supplements, typically at doses of 2.5 to 5 grams. The research is encouraging but not overwhelming. In one study of 16 male collegiate athletes, 5 grams per day for six weeks produced significant improvements in bench press, half squat, overhead press, and sumo deadlift strength compared to their own baseline. An overhead medicine ball throw, a proxy for power output, improved with a moderate effect size.
The limitation: when the betaine group was compared directly against the placebo group at the end of the study, there were no statistically significant differences on any measure. That’s an important distinction. It suggests the improvements may be real but modest enough that small studies can’t reliably detect them. The good news is that betaine supplementation had no negative effect on blood lipid profiles in these athletes, so it’s unlikely to cause harm in a fitness context at standard doses.
Mood and Cognitive Function
The link between TMG and mental health is indirect but plausible. TMG supports the production of SAM-e, and SAM-e has demonstrated antidepressant effects in animal research. In mice exposed to chronic stress, SAM-e reversed depression-like behaviors, increased brain-derived neurotrophic factor (a protein that supports brain cell growth), and improved the physical structure of synapses in the hippocampus.
The key caveat is that these studies used SAM-e directly, not TMG. Taking TMG should increase SAM-e production to some degree, but how much SAM-e actually rises in the brain from an oral TMG supplement hasn’t been well quantified in humans. Some people take TMG specifically as a cheaper, more stable alternative to SAM-e supplements, and anecdotal reports of mood improvement are common, but controlled human trials on TMG for depression or cognitive performance are lacking.
Dosage and Food Sources
Most supplement protocols use 1.25 to 3 grams taken twice daily, for a total of 2.5 to 6 grams per day. Doses up to 6 grams daily are considered safe for adults. For children, doses up to 150 milligrams per kilogram of body weight per day have been used safely.
You also get TMG from food, though the amounts are much smaller than what supplements provide. Wheat and wheat-based products are the richest sources, containing over 1,000 milligrams per 100 grams. Baked goods range from 33 to 226 milligrams per 100 grams depending on the product. Spinach, beets, and seafood (both shellfish and finfish) are also reasonable sources. Meats, poultry, fruits, nuts, and wine contribute very little, generally under 6 milligrams per 100 grams. A typical diet provides somewhere between 100 and 400 milligrams of betaine daily, well below supplement doses.
Side Effects and Risks
TMG is well tolerated at standard doses. The most commonly reported side effects are mild gastrointestinal symptoms like nausea, diarrhea, and stomach discomfort, which tend to resolve by splitting the dose across meals.
The one side effect worth watching is cholesterol. At doses above 4 grams per day, TMG has been shown to increase total cholesterol and LDL cholesterol. This is particularly relevant because the doses used clinically for homocysteine reduction (4 grams and up) overlap with the range where LDL rises become a concern. If you’re already managing high cholesterol, this trade-off matters. Lower doses in the 2.5 to 3 gram range, which are common in fitness-oriented supplementation, appear less likely to cause this effect, though monitoring is reasonable if you plan to take TMG long-term.
Who Benefits Most
TMG is most clearly useful for people with diagnosed homocysteine metabolism disorders, where it’s used as a medical treatment. Beyond that clinical niche, the strongest everyday case is for liver health, particularly if you have or are at risk for fatty liver disease. The athletic performance benefits are real but modest, roughly comparable to creatine’s more subtle effects. And the mood connection, while biologically logical, needs more human data before anyone can call it reliable.
For most healthy people eating a varied diet, TMG supplementation is safe and may offer incremental benefits, but it’s not a transformative supplement. If you decide to try it, staying at or below 6 grams daily and keeping an eye on cholesterol levels is a reasonable approach.