TMG (Trimethylglycine) UK Guide: What It Does, Who Needs It, When to Add It
TMG stands for trimethylglycine, also sold as betaine anhydrous. It is a small molecule made from the amino acid glycine plus three methyl groups, and its job in the body is to donate one of those methyl groups when the methylation cycle needs help clearing homocysteine.
In practical terms, TMG matters for three groups of UK buyers: people taking a high daily dose of NMN or NR, people with raised homocysteine on a blood test, and people with genuine methylation issues such as MTHFR variants. Everyone else can get plenty from beetroot, spinach, wheat germ and prawns.
This guide is written to be honest about where the evidence is strong (homocysteine reduction), where it is mixed (liver support) and where it is thin (mood, weight loss, cognition). We link to peer-reviewed trials rather than podcasts, and we flag where the sensible daily dose sits for a UK adult in 2026.
Key Takeaway
TMG (trimethylglycine) lowers plasma homocysteine in a dose-dependent way at 1.5 to 6 g a day, and is the specific methyl donor that offsets the methylation "tax" a high daily NMN dose puts on the body. Most UK adults on a varied diet do not need it, but anyone taking 500 mg or more of NMN, or with raised homocysteine, should consider 500 to 1,000 mg TMG daily alongside a methylated B12.
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In this article
- What is TMG (trimethylglycine) and why does it matter?
- What does TMG actually do in your body?
- Why do NMN users add TMG to their stack?
- What does the evidence say for homocysteine?
- Does TMG actually support liver health?
- What is the sensible daily TMG dose?
- When should you take TMG, and with what?
- What UK foods give you TMG naturally?
- Who should skip or be careful with TMG?
- How does TMG compare to choline?
- Frequently asked questions
- The bottom line for UK buyers in 2026
What is TMG (trimethylglycine) and why does it matter?
TMG is short for trimethylglycine, and on a supplement label you will also see it as betaine anhydrous. The two names describe the same molecule: glycine plus three methyl groups attached to its nitrogen, which is where the "tri-methyl" comes from.
Chemically, TMG is a natural compound found in beetroot (which is where the name betaine comes from, after the Latin Beta), spinach, quinoa, wheat germ and shellfish. In the body it acts as an osmolyte, helping cells manage water balance, and as a methyl donor in the methionine cycle (Craig, 2004, DOI: 10.1093/ajcn/80.3.539).
The methylation cycle is one of the most important background reactions in human biochemistry. It attaches methyl groups to DNA, neurotransmitters, hormones and detox pathways, and it depends on a small pool of methyl donors that includes folate, B12, choline and TMG.
What does TMG actually do in your body?
TMG has two well-established jobs. First, it donates one of its three methyl groups to convert homocysteine back into methionine, which is important because chronically high homocysteine is linked to cardiovascular risk. This reaction is catalysed by the enzyme betaine-homocysteine methyltransferase (BHMT), which sits mostly in the liver and kidneys (Ueland, 2011, DOI: 10.1007/s10545-010-9088-4).
Second, it works as an osmolyte, stabilising proteins and cell membranes under stress. This is why TMG sometimes shows up in performance and hydration products, though the evidence for exercise benefit is much thinner than for homocysteine.
What TMG does not do reliably in humans is boost mood, burn fat or "detox" the body. Product marketing often stretches those claims, but the clinical evidence sits behind homocysteine and, at higher doses, some liver enzyme markers.
Why do NMN users add TMG to their stack?
This is the reason TMG suddenly appeared on UK longevity shelves. When your body raises NAD+ using NMN, the excess nicotinamide is eventually cleared by methylation, using up methyl groups from S-adenosylmethionine (SAM). If you take 500 mg or more of NMN a day for months, that clearance pathway runs a bit hotter than it evolved for.
Podcasters like David Sinclair popularised the idea of "methyl-donor tax" and started pairing NMN with TMG to top up the SAM pool. The biochemistry is sound and TMG's methyl donation via BHMT does help regenerate methionine, which in turn regenerates SAM. It is a sensible add-on, not a cure for a well-documented harm.
At typical 250 mg NMN doses, most people do not need TMG. Above 500 mg NMN, especially long-term, adding 500 to 1,000 mg TMG a day is a reasonable insurance policy, and pairing it with a methylated B12 keeps the whole one-carbon cycle stocked. If you already take a combined product like our NMN Complex with Resveratrol, the 600 mg of TMG in the full serving already covers this.
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What does the evidence say for homocysteine?
This is the strongest use case for TMG. In a 2003 dose-response trial, healthy adults taking 1.5, 3 or 6 g of betaine a day for one-week periods saw fasting plasma homocysteine fall by roughly 5%, 10% and 14% at each dose. The 3 g dose is the pragmatic middle, and the drop was highly significant against baseline (Olthof et al., 2003, DOI: 10.1093/jn/133.12.4135).
A 2013 meta-analysis pooling five randomised trials with 133 participants confirmed the finding: betaine at doses from 1 to 6 g a day reduced plasma homocysteine by an average of 1.23 to 1.58 µmol/L, again in a dose-related manner (McRae, 2013, DOI: 10.1016/j.jcm.2012.11.001). The effect held whether homocysteine was raised or already within range.
What the Research Says
Olthof and colleagues (J Nutr, 2003) gave 34 healthy men and women 1.5, 3 or 6 g of betaine (TMG) for consecutive one-week periods and measured fasting plasma homocysteine. Homocysteine fell in a clear dose-response manner (roughly 5%, 10% and 14% at each step). Six grams a day was the largest reduction, but the 3 g dose is usually enough for a normal-range adult who simply wants insurance against the higher end of the reference range.
For context, high homocysteine is measured in the UK as a blood test through your GP (usually a private "add-on" test, or ordered on the NHS if there is a specific clinical indication). Alongside TMG, the other lever is folate plus B12: our methylcobalamin B12 guide and methylfolate guide cover the two other pieces.
Does TMG actually support liver health?
The liver story is more mixed than the marketing suggests. TMG is genuinely made in the liver from choline, and it supplies methyl groups for hepatic detox reactions, so the mechanism is real. But the outcome trials are less impressive than podcasters imply.
A 2009 randomised placebo-controlled trial in Hepatology gave 55 people with biopsy-proven non-alcoholic fatty liver disease (NAFLD) 20 g of betaine a day for 12 months. Steatosis (fat accumulation) improved on liver biopsy, but the ballooning, inflammation and fibrosis scores that define the more serious NASH stage did not improve significantly (Abdelmalek et al., 2009, DOI: 10.1002/hep.23239).
In plain terms: betaine helped clear fat from the liver, but did not reverse the deeper injury that matters for long-term outcomes. It is a reasonable adjunct for someone with early fatty liver who is also fixing diet and alcohol, and it is not a substitute for the primary interventions. If liver support is your main reason for shopping, our dedicated milk thistle for liver health UK guide covers the wider picture, and our Liver Complex bundles choline (a TMG precursor) with silymarin, NAC and 12 other botanicals.
What is the sensible daily TMG dose?
The label doses in the trials are the honest benchmark. The Olthof 2003 study used 1.5 to 6 g, most consumer capsules aim at 500 to 1,000 mg, and combination products like our NMN Complex land at 600 mg per full serving on the practical assumption that most buyers will not tolerate the taste of 3 g of loose betaine powder every morning.
The table below sets sensible targets by goal and evidence grade. All doses are for adults, taken with food, and combined with dietary betaine from beetroot, spinach or wheat.
| Goal | Sensible daily TMG | Evidence grade | Trial length used |
|---|---|---|---|
| Lowering raised homocysteine | 1.5 to 3 g | Strong (multiple RCTs) | 6 to 24 weeks |
| Methyl donor support alongside high-dose NMN | 500 to 1,000 mg | Mechanistic, no long-term human trial | Ongoing while NMN is taken |
| Fatty liver adjunct | 1 to 2 g | Mixed (steatosis yes, NASH no) | 12 months |
| Exercise performance / power output | 2.5 g | Modest, mixed by protocol | 2 to 15 days |
| General "healthy" adult, no specific issue | Skip capsules, hit food targets | Weak beyond food intake | Not applicable |
When should you take TMG, and with what?
Timing is not fussy. TMG is water-soluble and stable, so take it with a main meal to blunt the mildly fishy taste some people notice with powders, and to slow absorption a little.
If you take a methylated multivitamin or a folate plus B12 stack, take TMG in the same window. The methylation cycle uses all three, and there is no benefit to spacing them out.
If you take NMN in the morning, take TMG in the morning too. Pairing them lines up with the Sinclair-stack rationale and it keeps supplement admin simple. Our when to take NMN UK guide covers the timing detail for the NAD+ side of the stack.
What UK foods give you TMG naturally?
Most UK adults eating a varied diet get 100 to 400 mg of betaine a day without trying, which is one reason capsules are unnecessary for the general population. The richest UK sources are beetroot, spinach, quinoa, wheat germ and prawns.
A rough guide by 100 g serving, drawn from the food composition data cited in the Craig review: cooked spinach ~600 to 700 mg, wheat germ ~1,300 mg, quinoa ~600 mg, beetroot ~120 to 250 mg, prawns ~80 mg (Craig, 2004, DOI: 10.1093/ajcn/80.3.539). A single 100 g portion of wheat germ or spinach exceeds most consumer TMG capsule doses.
The practical read is that if you eat beetroot, greens and whole grains regularly, you already hit the range where TMG supplements move homocysteine. If your diet leans processed and low in these foods, a modest capsule dose is a reasonable insurance policy.
Who should skip or be careful with TMG?
TMG is well tolerated for most adults at 500 to 3,000 mg a day. The one consistent side effect from higher doses is a modest rise in total and LDL cholesterol, which showed up in the Olthof 2003 study and has been confirmed in later meta-analyses.
Worth Knowing
TMG at doses above 3 g a day has been shown to raise total and LDL cholesterol by 5 to 10% in healthy adults. If you have known high cholesterol, familial hypercholesterolaemia or existing cardiovascular disease, stay under 1 g a day, take it with your statin routine, and speak to your GP if a lipid panel is due. This is a real, documented side effect of the higher doses used for homocysteine and NAFLD trials, not a marketing scare.
Skip TMG entirely if you are pregnant or breastfeeding (no human safety data), under 18, or on kidney dialysis. The BHMT reaction happens in the liver and kidneys, so anyone with advanced chronic kidney disease should treat TMG as a discuss-with-clinician supplement rather than an over-the-counter add.
Anyone with confirmed MTHFR C677T variants should still start with a methylated folate plus methylated B12 stack first, then add TMG only if a subsequent homocysteine test is still raised. Adding methyl donors on top of methyl donors without a target measurement can push homocysteine too low and drive fatigue or mood shifts in a minority of people.
How does TMG compare to choline?
Choline and TMG sit next to each other in the methylation cycle. Choline is oxidised in the liver to betaine (TMG), which is then used to methylate homocysteine. If you take choline, you make TMG downstream; if you take TMG, you skip the oxidation step.
The practical differences are dose, cost and side effect profile. Choline has a UK EFSA-authorised claim for "normal liver function" at 82.5 mg per portion, which is why our Liver Complex is dosed to that threshold. TMG does not have a food supplement authorised health claim in the UK.
For homocysteine, TMG has more direct human trials; for liver support, both are reasonable but neither replaces alcohol under 14 units a week and a Mediterranean diet. For NMN pairing, TMG is the specific molecule the biochemistry names, so it is the more literal fit. See our milk thistle liver guide for how choline slots into a wider liver-support stack.
Key Takeaway
If you take standalone NMN at 500 mg a day, add 500 to 1,000 mg of TMG plus a methylated B12 and you have covered the methylation-tax question sensibly. If you take a combination product like our NMN Complex, the 600 mg TMG and 150 mcg methylcobalamin are already in the serving, so no separate TMG is needed.
Frequently asked questions
Is TMG the same as betaine anhydrous?
Yes. TMG (trimethylglycine) and betaine anhydrous are two names for the same molecule, and the two words are used interchangeably on UK supplement labels. Betaine HCl is a different product used for stomach acid support and is not the same thing.
Do I really need TMG if I take NMN?
At 250 mg NMN a day most people do not need extra TMG, and a normal diet plus a methylated B12 usually covers methylation demands. At 500 mg or more of NMN long-term, adding 500 to 1,000 mg TMG is a sensible insurance policy that fits the underlying biochemistry.
What is the best time to take TMG?
Take TMG with a main meal, ideally the same meal as your NMN or methylated B-vitamin stack. Morning with breakfast is the simplest routine and keeps admin low. There is no evidence that splitting the dose across the day helps.
Can TMG lower homocysteine on its own?
Yes. Randomised trials from 1 to 6 g of betaine a day show a dose-dependent drop in plasma homocysteine of around 5 to 14% (Olthof, 2003). It works best when folate and B12 status are also adequate, because the methionine cycle uses all three.
Does TMG raise cholesterol?
At doses above 3 g a day, TMG has been shown to raise total and LDL cholesterol by roughly 5 to 10% in healthy adults. At the 500 to 1,000 mg doses used in most consumer capsules the effect is small to negligible, but anyone with known high cholesterol should stay at the low end and monitor with a lipid panel.
Is TMG safe in the UK long-term?
TMG is legal as a food supplement in the UK and is well tolerated at 500 to 3,000 mg a day in adults. Avoid during pregnancy and breastfeeding due to lack of safety data, and speak to your GP if you have advanced kidney disease or existing cardiovascular disease.
Can I get enough TMG from food?
Most UK adults on a varied diet get 100 to 400 mg of betaine a day. Wheat germ, spinach, quinoa, beetroot and prawns are the richest sources. If those foods are regular in your week and your homocysteine is in range, you do not need a supplement.
The bottom line for UK buyers in 2026
TMG is not a universal add-on. It is the right supplement for a specific person: someone taking 500 mg or more of NMN long-term, someone with a raised homocysteine result, or someone with an MTHFR variant whose folate plus B12 stack has not moved the number enough.
For everyone else, TMG is a nice-to-have that a good UK diet already covers. Spinach, beetroot, quinoa and wheat germ do the same job as 500 mg of betaine anhydrous, without the taste, cost or cholesterol nudge.
If TMG does fit your profile, the sensible move is either a combination product like our NMN Complex that already includes 600 mg of TMG plus methylated B12, or standalone NMN plus a separate TMG capsule if you want to fine-tune the dose. Both are legitimate stacks; the combination is usually better value.
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