Glycine vs Creatine: Which Is Better?

Summary

The video compares glycine and creatine across exercise performance, brain health, sleep, metabolism, skin and bone health, and longevity. The presenter’s overall conclusion is that creatine has stronger evidence for increasing muscle strength and exercise performance, while glycine appears to have broader potential health benefits. The video’s hypothetical scorecard ends 4–2 in favor of glycine, though the presenter notes that creatine could receive an extra point for its substantial strength and power benefits.

How glycine relates to creatine

The body uses glycine to make creatine:

• In the kidneys and other tissues, the enzyme AGAT combines glycine with a chemical group from arginine, producing guanidinoacetate.
• Mainly in the liver, GAMT adds a methyl group—supplied by SAM—to make creatine.
• Creatine travels to tissues, including muscle and brain, where it helps regenerate ATP.
• The presenter says the body loses about 2 g of creatine daily and uses roughly 0.6 g of glycine to produce 1 g of creatine.

However, taking glycine is not equivalent to taking creatine. Glycine also contributes to collagen, heme, and glutathione production, and the presenter argues that the body’s needs for these functions exceed what it makes on its own.

Comparison by health area

• Muscle and strength — Creatine advantage. Creatine increases muscle phosphocreatine, helping replenish ATP during repeated high-intensity exercise. The presenter cites a 2014 meta-analysis in which creatine added to strength training produced greater gains than placebo—about 4.4 kg more in upper-body exercises and 11.4 kg more in lower-body exercises. A 2024 meta-analysis found about 1.14 kg more lean body mass and 0.88% less fat, though the presenter cautions that some apparent lean-mass gain may be water stored in muscle.

Glycine is not generally considered a muscle-building supplement. The video describes promising but limited findings: a study in hemodialysis patients found better body-composition results with glycine than with BCAAs, and a study of glycine plus NAC in older adults reported improved grip strength and body composition. The proposed explanation involves glutathione, inflammation, and insulin sensitivity, but the presenter says it is unclear whether these findings apply to healthy gym-goers.

• Brain and cognition — Potentially different benefits from both. Creatine may support brain energy availability. Meta-analyses cited in the video report some memory benefits, particularly in older adults, but no consistent overall improvement in cognition or executive function. Glycine plays a role in neurotransmission, including at inhibitory glycine receptors and as a co-agonist at NMDA receptors involved in learning and memory. The presenter also discusses high-dose glycine research in schizophrenia and possible neuroprotective effects related to glutathione. Evidence for glycine’s cognitive effects is limited, and some cited findings used it with NAC rather than alone. The video gives a point to each supplement for their different potential effects.

• Sleep — Glycine advantage. The presenter says glycine has researched sleep benefits, while creatine has not been shown to directly improve sleep and may reduce “sleep pressure.” Both supplements are described as having promising results for fatigue or cognitive performance around sleep deprivation: a cited creatine study found that a large dose reversed cognitive decline after 21 hours awake, while glycine has been associated with less next-day fatigue and better alertness after partial sleep deprivation.

• Blood sugar and metabolic health — Glycine advantage. In evidence described in the video, 5 g of glycine taken with glucose reduced the glucose response by more than 50% compared with glucose alone, without increasing overall insulin secretion. A study in people with type 2 diabetes reportedly found that 15 g of glycine per day for three months lowered HbA1c and several inflammation markers. A small trial also found improved HbA1c when creatine was combined with exercise, but the presenter considers glycine’s evidence more direct and promising.

• Skin and bone — No score awarded. Glycine is a major component of collagen and is needed for collagen renewal. The presenter notes that research supports collagen peptides for skin, but not glycine alone. Small studies of topical creatine creams have reported improvements in skin firmness and elasticity, but the creams included other ingredients. For bone health, the video mentions animal research suggesting a possible glycine benefit, while two trials in postmenopausal women found no added bone-density benefit from creatine combined with resistance training. The presenter considers the evidence too limited to score either supplement.

• Longevity — Glycine advantage, with uncertainty. The video cites mouse research in which glycine extended average lifespan by 4–6%, while GlyNAC extended lifespan by 24%. One study of female mice reported roughly 9% longer healthy lifespan with creatine, but other creatine studies found no lifespan effect. The presenter therefore views the animal evidence for glycine as more consistent, while emphasizing that these are not human lifespan results. The presenter also says creatine can reduce the improvement in VO₂ max gained from training, which is one reason he does not take it continuously.

The presenter’s scorecard and personal approach

The score progresses as follows:

• Muscle and strength: Creatine gets a point.
• Brain health: Both get a point for different potential benefits.
• Sleep: Glycine gets a point.
• Blood sugar: Glycine gets a point.
• Skin and bone: No points, because the evidence is insufficient.
• Longevity: Glycine gets a point.

Final score: glycine 4, creatine 2. The presenter stresses that the tally is hypothetical and says giving creatine an additional point for strength and power would also be reasonable.

The presenter says he takes 10 g of glycine daily, mainly for longevity and collagen turnover, but does not take creatine every day. He says he already has sufficient muscle and strength for his longevity goals, follows an omnivorous diet that supplies creatine, and is interested in avoiding any possible effect of creatine on VO₂ max gains. He also argues that glycine is harder to obtain from food than creatine, since dietary glycine is especially associated with gelatin, skin, and ligaments. These are the presenter’s personal reasons and interpretation, not universal recommendations.

Other material in the video

The presenter promotes a health and fitness community, citing members’ reported improvements in push-ups, weight, VO₂ max, and HbA1c, as well as his own reported changes in VO₂ max, visceral fat, and a health-biomarker score. These examples are presented as testimonials rather than controlled research evidence.

Speakers and sources featured

• Speaker: The video’s single narrator and presenter, associated with the Siim Land channel. No other speaking voices are apparent in the subtitles.
• Research sources discussed: The narrator refers to studies and reviews but does not provide authors or publication titles. These include:
  • A 2014 meta-analysis of 23 creatine-and-strength-training studies.
  • A 2024 meta-analysis of 12 studies on creatine, body composition, and strength training.
  • A glycine-versus-BCAA crossover study in hemodialysis patients.
  • Research on glycine plus NAC in older adults and in people with HIV.
  • A 2023 meta-analysis and a 2024 meta-analysis of creatine and cognition.
  • Human studies of high-dose glycine added to schizophrenia medication.
  • A 2024 creatine sleep-deprivation crossover study and studies of glycine after sleep deprivation.
  • Studies of glycine and creatine in blood-sugar control, topical creatine creams, and creatine with resistance training in postmenopausal women.
  • Animal studies of glycine, GlyNAC, and creatine related to lifespan and bone density.
• Additional sources: Unnamed members of the presenter’s Top 1% Health community, whose results are cited as testimonials.