Beet it: Could betaine help you set a new personal gym record? Original paper

Betaine, or trimethylglycine, is a naturally occurring byproduct of sugar beet refinement. In addition to beets, betaine is found in wheat, spinach, and shrimp.^[1] Betaine has two major physiological roles in the body: it acts as an osmolyte (i.e., it regulates water balance in cells) and a methyl group donor. Some evidence suggests that supplementation with betaine enhances exercise performance, but the evidence is mixed. Fewer studies have evaluated the effect of supplementation with betaine on endocrine function, but betaine has been shown to increase IGF-1 and decrease cortisol in response to acute bouts of resistance exercise.^[2]

Adapted from Zeisel et al., 2003^[1]

In this 14-day randomized crossover trial, 10 adolescent male handball players (average age of 16) without prior resistance training experience supplemented with either 2.5 grams of betaine or placebo daily. At the end of each supplementation period, the participants performed 5 sets of leg press followed by 5 sets of barbell bench press. For both exercises, the participants used 80% of their 1-repetition maximum (1RM), performed each set to volitional fatigue, and rested for two minutes between sets. There was a 5-minute rest interval between exercises. The interventions were separated by a washout period of 30 days.

Venous blood samples were collected before each supplementation period and before and after the resistance exercise sessions. The outcomes assessed were repetitions performed on the leg press and bench press and plasma levels of total testosterone, cortisol, and lactate.

Compared to placebo, betaine increased repetitions performed on the leg press (36 vs. 25) and bench press (36 vs. 26). Additionally, compared to placebo, betaine increased resting total testosterone levels and decreased cortisol and lactate levels. Following the resistance exercise sessions, betaine decreased cortisol levels and lactate and increased total testosterone, compared to placebo.

Although the participants were instructed to refrain from strenuous physical activity 48 hours before the resistance exercise sessions and to consume the exact same diet during this period, diet and physical activity were not standardized during the rest of the 14-day interventions.

Baseline testosterone levels were on the lower end of the normal range for 16–18-year-old boys, which may have influenced the results.

Studies that have investigated the effect of supplementation with betaine on resistance exercise performance have produced mixed results. However, the experimental designs and the assessed outcomes have also widely varied between these studies.

Researchers have speculated that betaine may have an ergogenic effect in resistance exercise protocols that challenge muscular endurance with high levels of metabolic stress,^[3] such as those employing short rest periods and higher training volumes. This hypothesis is supported by the results of the present study, among others.

A 2-week study published in 2011 reported that supplementation with betaine increased the number of repetitions performed in the machine bench press.^[4] The participants performed 10 sets using 50% of 1RM. Each set was performed to volitional fatigue, and there was a 2-minute rest interval between sets. In a study published in 2018, supplementation with betaine increased the amount of training volume performed over the course of an 8-week resistance exercise intervention.^[5] The resistance exercise program included two lower body sessions per week and one upper body session. Each session consisted of multiple exercises performed for 3 sets of 8–12 repetitions to volitional fatigue, with 1–2 minutes of rest between sets.

However, a 6-week study published in 2020 reported that supplementation with betaine did not improve performance on the Bergeron Beep Test,^[6] which involves performing 7 thrusters, 7 pull-ups, and 7 burpees in less than one minute (with the remainder of the minute used for rest) until exhaustion.

Several mechanisms have been proposed to explain betaine’s potential ergogenic effect. Perhaps the most compelling is betaine’s effect on lactate levels. Lactate levels are correlated with anaerobic power output.^[7] The present study showed that supplementation with betaine reduced lactate levels after exercise, which is notable because significantly more work was performed in this condition compared to the placebo.

In agreement with this result, other studies have reported that supplementation with betaine increased the amount of work performed without producing greater lactate levels.^[4][8] Lactate levels are associated with the development of fatigue during high-intensity resistance exercise,^[9] so attenuating the rise in lactate levels may explain betaine’s potential ergogenic effect.

How exactly betaine reduces lactate levels is unclear. Through its role as a methyl donor, betaine is involved in converting homocysteine into methionine, which is then used to form s-adenosylmethionine, a substrate used to synthesize creatine. Therefore, supplementation with betaine could increase skeletal muscle phosphocreatine content, shifting ATP synthesis during exercise away from glycolytic metabolism and toward the breakdown of phosphocreatine, reducing lactate production. However, though this effect has been shown in livestock,^[10] it has yet to be demonstrated in humans.^[11]

Another idea is that betaine enhances mitochondrial respiration,^[12][13][14] and thus increases lactate breakdown. Betaine’s potential ergogenic effect may also stem from its role as an osmolyte — it helps to sustain cellular hydration in the face of physiological stressors like exercise, and as a consequence, maintains a favorable environment for muscle contraction.^[3]

Betaine appears less likely to benefit resistance exercise performance when only 1–3 sets to volitional fatigue are performed,^[15][16] although positive results have been reported, or when high intensities (more than 80% of 1RM) and long rest intervals (more than 2 minutes) are used.^[16][17] Furthermore, supplementation with betaine failed to enhance maximal strength or power in most studies.^[18]

With respect to endocrine function, a 2021 study of youth professional soccer players (average age of 15) reported that supplementation with betaine throughout a 16-week season increased testosterone levels and improved participant testosterone to cortisol ratio, compared to a placebo.^[19] However, there were no differences between groups for changes in growth hormone or IGF-1 levels. In addition, a 2-week study published in 2013 found that supplementation with betaine increased IGF-1 and growth hormone and decreased cortisol levels following the completion of a full-body workout.^[2]

As it stands, supplementation with betaine seems to improve resistance exercise performance in protocols that generate high levels of metabolic stress, as well as markers of endocrine function, but further research is needed to confirm these findings.