Betaine (TMG): Does It Actually Work?

What it is

Betaine — also called trimethylglycine, or TMG — is a naturally occurring compound found in beetroot, spinach, quinoa and wholegrains. In the body it serves two distinct roles: it acts as an osmolyte, helping cells regulate fluid and withstand stress, and as a methyl donor, supplying methyl groups that feed into homocysteine metabolism, creatine synthesis and numerous other biochemical pathways. Those two mechanisms are why it appeared on supplement formulators' radar as a potential performance compound.

The sports supplement form is betaine anhydrous — a crystalline powder usually dosed at 1.25–2.5 g per serving, often found inside pre-workouts or sold standalone.

Does it work? The evidence

Betaine earns a Grade C here — which means the evidence is limited or mixed, not that it has been disproved. That distinction matters. Several rigorous trials exist; the results just do not align cleanly.

Power and strength (Grade C). A number of controlled trials — including a 2017 review published in the Journal of the International Society of Sports Nutrition — found improvements in bench-press power, squat performance and total training volume at 2.5 g/day over 6–14 weeks. Other trials, matched in design, found no significant difference versus placebo. Meta-analyses aggregate these results into modest, inconsistent effect sizes — meaningful enough to keep betaine in the conversation, not strong enough to call it established.

Body composition (Grade C). Some trials show modest reductions in fat mass and improvements in lean body mass alongside resistance training. Again, the effect disappears in other cohorts. The signal exists; it is not robust.

For comparison: creatine monohydrate has Grade A evidence for both strength and lean mass — it is the non-negotiable foundation. Betaine is, at best, a secondary stack addition once that base is covered.

How to take it

The evidence base is built almost entirely on 2.5 g per day, typically split into two doses of 1.25 g. There is no established loading phase; effects appear to accumulate over weeks of consistent use rather than acutely.

Timing is not critical. Many people take one dose pre-workout and one with another meal. If you are buying a pre-workout that contains betaine, check the dose — anything below 1.25 g per serving is likely underdosed.

General information, not medical advice — check with a GP or pharmacist before starting, especially if pregnant, breastfeeding, under 18, or on medication.

Who should take it — and who shouldn't

May be worth considering if you:

• Are an intermediate or advanced lifter who has already optimised your protein intake, creatine, sleep and training programme.
• Compete or train in strength, power or high-volume hypertrophy contexts — the studied populations.
• Are comfortable trialling a supplement with mixed but non-zero evidence.

Skip betaine if you:

• Are a beginner — the fundamentals (protein, creatine, caffeine, sleep, structured training) will deliver far more than betaine ever could.
• Are pregnant or breastfeeding.
• Have elevated cholesterol — some individuals experience an increase on TMG, so monitor if relevant.
• Are on a tight budget — spend that £ on higher-certainty supplements first.

Betaine is not a foundation supplement. Think of it as a potential 1–2% add-on for someone whose other 98% is already built. Supplements as a whole are roughly 5% of your result — the training, nutrition, sleep and consistency underneath are the other 95%. If that 95% isn't locked in, no supplement will compensate. A free Blueprint quiz is a fast way to see where your biggest levers actually are.

Safety & interactions

Betaine anhydrous has a reasonable safety record at 2.5 g/day in healthy adults. The most commonly reported side effects are:

• GI discomfort — nausea or loose stools, particularly at higher doses or on an empty stomach.
• Fishy body odour — caused by excess trimethylamine production, similar to what some people experience with choline or fish oil supplements.
• Cholesterol elevation — a subset of trial participants showed increases in total cholesterol. If you have dyslipidaemia or are monitoring cardiovascular risk markers, track your levels before and after starting.

There are no serious known drug interactions at the studied dose, but the methyl-donor activity means theoretical interactions with medications that affect one-carbon metabolism (e.g., methotrexate) cannot be fully ruled out — consult your GP or pharmacist if relevant.

How to buy it well

Betaine is inexpensive as a standalone powder. When buying:

• Look for third-party testing — Informed-Sport certification is the gold standard for athletes in tested sports, ensuring the batch is free from prohibited substances and accurately labelled.
• Dose matters — confirm 2.5 g total daily is achievable from your chosen product; many pre-workout blends underdose it.
• Standalone vs blend — a pure betaine anhydrous powder gives full dose control and is typically cheaper than a fancy pre-workout built around it.

If you are already taking creatine and beta-alanine, betaine is one of the more plausible next additions in a sports stack — but apply the same label scrutiny you would to any compound.

The verdict

Betaine is Situational. The mechanistic rationale is credible, the safety profile is acceptable, and some controlled trials show genuine strength and body-composition benefits at 2.5 g/day. But the literature is inconsistent enough that it does not belong on the same level as creatine, adequate protein or caffeine.

If you are an experienced lifter with your fundamentals fully dialled in and you want to experiment with a low-risk add-on, betaine is a reasonable candidate. If you are still building your foundation, the money and attention are better spent elsewhere.

Supplements are the final 5% — the coaching, programming, nutrition and recovery underneath do the heavy lifting. Want to get that 95% right? Book a free consultation and we will map out exactly what you need.