Trimethylglycine, Homocysteine, and Exercise Performance

What the evidence shows

Trimethylglycine can lower plasma total homocysteine in several controlled human studies.
Homocysteine changes have not been shown to translate reliably into better exercise performance.
Recent reviews suggest possible benefits for some lower-body strength and jumping outcomes, but not consistently for endurance, sprint power, or muscular endurance.
Endurance evidence is especially limited, with few studies and high risk of bias.
Most research involved small groups of healthy adults or athletes, so generalization to other populations remains uncertain.
Protocol differences in duration, training status, outcome testing, and study design likely contribute to conflicting results.

What trimethylglycine is being studied for

Trimethylglycine is the same compound commonly called betaine. In human metabolism, it can provide a methyl group for the remethylation of homocysteine, so researchers have examined whether supplemental betaine changes blood homocysteine concentrations.

Exercise studies have asked a different question: whether betaine changes strength, power, muscular endurance, oxygen consumption, sprint ability, or other performance measures. A lower homocysteine result should not automatically be interpreted as evidence of better athletic performance.

The two research areas overlap biologically, but they use different outcomes and often study different populations.

What human research has established about homocysteine

The clearest human finding is that betaine can lower plasma total homocysteine in some study settings. In a randomized, double-blind crossover study of 10 healthy adults with normal body weight, single oral exposures produced an acute, dose-related reduction in plasma total homocysteine at the higher tested amounts, with the reduction appearing within hours.

Longer studies have also reported lower homocysteine. A randomized trial in 42 adults with obesity used betaine alongside a calorie-restricted diet for 12 weeks. Homocysteine fell in the betaine group, but body weight and fat mass did not improve more than with the diet alone. Total and LDL cholesterol were higher in the betaine group, which adds context to the result rather than supporting a simple benefit narrative.

A later randomized crossover study in young, physically active men also reported lower homocysteine after several weeks of betaine exposure. Taken together, these trials support a biochemical effect on homocysteine, but they do not establish that lowering homocysteine improves exercise capacity or long-term health outcomes.

Which populations were studied

The human evidence is concentrated in relatively small groups of generally healthy adults or recreationally active participants.

Healthy adults with normal body weight were studied in the acute homocysteine experiment.
Adults with obesity were studied while following a calorie-restricted diet.
Young, physically active men were studied in a crossover biomarker trial.
Exercise trials have included resistance-trained men, recreational athletes, and younger competitive athletes.
Recent reviews of exercise research largely concern healthy people rather than patients with diagnosed metabolic conditions.

Women, older adults, elite endurance athletes, and people with persistently high homocysteine are less well represented in the exercise literature. That limits how confidently results can be generalized across age, sex, training level, diet, and medical status.

What the exercise evidence actually shows

The exercise findings are mixed rather than uniformly positive. A 2024 systematic review and meta-analysis included 17 chronic-supplementation studies with 317 participants, of whom 21% were female. It reported a significant pooled effect for maximal strength, particularly lower-body strength, and a smaller effect for vertical jumping after excluding a low-quality study. It did not find significant effects for upper-body strength, cycling sprint power, bench-press-throw power, or muscular endurance.

Endurance evidence is thinner. A 2025 systematic review found only five eligible studies, using three parallel-group designs and two crossover designs. Two studies reported improvements involving maximal oxygen consumption or late-stage Wingate power, while other findings concerned power, oxygen consumption, or blood lactate. The review rated all included studies as having high risk of bias and described the evidence as limited and inconclusive.

The most defensible interpretation is that betaine may influence some strength or power outcomes in selected protocols, but a reliable improvement across exercise types has not been established.

Why results differ by protocol

Different studies are not testing exactly the same intervention. Some examine an acute exposure and a short-term blood marker; others use several weeks of daily supplementation during resistance training, endurance testing, or a competitive season.

The performance tests also differ substantially. A laboratory strength test, a vertical jump, a repeated-sprint test, a Wingate test, and a cycling time trial do not measure the same physiological capacity. A result in one test cannot be assumed to transfer to another.

Important design differences include:

placebo control and randomization quality
crossover versus parallel-group assignment
supplementation duration
training status and concurrent training programs
sex, age, diet, and baseline homocysteine
whether the outcome was a direct performance measure or a physiological marker

Small samples make isolated positive findings especially vulnerable to chance, baseline imbalance, and differences in training or testing conditions.

What remains uncertain

Human research has not established that betaine’s effect on homocysteine produces a meaningful improvement in exercise performance. It is also unclear whether people with higher baseline homocysteine respond differently from people whose levels are already within a typical range.

The exercise literature needs larger, better-controlled trials with prespecified outcomes, consistent performance tests, transparent reporting, and enough women and older adults to assess whether results differ by population. Studies should also separate changes in blood biomarkers from changes that matter directly to performance.

Safety and longer-term tradeoffs remain relevant uncertainties. The obesity trial found higher total and LDL cholesterol in the betaine group, while many exercise studies were too small or too short to characterize uncommon or delayed effects. The current evidence therefore supports a measured conclusion: homocysteine lowering is better established than performance enhancement, and neither finding should be treated as a guarantee of benefit for an individual.

Sources

About this article

NootroWorld publishes research summaries, not medical advice. This article describes what studies have and have not established; it does not tell you what to take. Supplements can interact with medication, pregnancy and existing health conditions, and study populations often differ from your own situation. Discuss any personal decision with a qualified healthcare professional.