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Head-to-head evidence comparison — which supplement is right for you?
Caffeine wins 2 of 3 categories. Both are solid choices — the best pick depends on your specific goals.
Verdict
Likely helps
22 of 25 studies with measurable effects showed benefit.
Top outcomes
Verdict
Mostly mechanism / observational
2 of 2 studies with measurable effects showed benefit.
Top outcomes
Shared outcomes (1)
Outcomes where both Caffeine and Glycerol have evidence — compare verdict strength side-by-side.
100-200mg
Morning, 30-60 minutes before exercise
Pill/capsule for precise dosing
1-1.5g per kg body weight
1-2.5 hours before endurance exercise, Consume with large volume of fluid (1-2L)
Glycerol powder (65% concentration typical)
15-45 minutes
30-60 minutes
30-60 minutes
30-60 minutes
During exercise (1-3 hours post-ingestion)
During exercise in heat
During exercise
1-2 hours post-ingestion
Effect of Acute Caffeine Intake on the Fat Oxidation Rate during Exercise: A Systematic Review and Meta-Analysis
Nutrients (2020) · Meta analysis · n=2020
A subsequent meta-analysis was performed using the random effects model to calculate the standardized mean difference (SMD).
The effects of caffeine intake on weight loss: a systematic review and dos-response meta-analysis of randomized controlled trials
Critical reviews in food science and nutrition (2019) · Meta analysis · n=606
Thirteen RCTs with 606 participants were included in the meta-analyses.
Effect of Caffeine and Nitrates Combination on Exercise Performance, Heart Rate and Oxygen Uptake: A Systematic Review and Meta-Analysis
Nutrients (2024) · Meta analysis · n=95
The meta-analysis revealed that caffeine and nitrates supplementation (CAF+nitrates) did not enhance performance in time trials (TTs) over the CAF alone (g = -0.06; 95% CI = -0.46 to 0.35; p = 0.78) or nitrates alone (g = 0.29; 95% CI = -0.12 to 0.70; p = 0.17).
Nutritional Ergogenic Aids in Combat Sports: A Systematic Review and Meta-Analysis
Nutrients (2022) · Meta analysis
In this regard, abilities including the number of attacks, reaction time, handgrip strength, power and TTE, among others, were improved.
The effect of pre-exercise oral hyperhydration on endurance exercise performance, heart rate, and thermoregulation: a meta-analytical review
Applied physiology, nutrition, and metabolism = Physiologie appliquee, nutrition et metabolisme (2024) · Meta analysis
Meta-analysis determined overall effect size (Hedges' g), and meta-regression the influence of independent moderators (ambient temperature, hyperhydration agent, exercise mode, extent of hyperhydration).
Meta-analysis: Effects of glycerol administration on plasma volume, haemoglobin, and haematocrit
Drug testing and analysis (2013) · Meta analysis
The meta-analysis revealed that the increase in plasma volume was 3.3% larger (95%-CI: 1.1-5.5%) after glycerol administration when compared to fluid only.
Based on multiple meta-analyses showing 3-6mg/kg optimal dosing. Performance benefits plateau around 200-300mg with increased jitteriness at higher doses.
Based on meta-analysis showing hyperhydration effects on endurance. Conservative effectiveness given limited direct glycerol performance studies in the provided evidence. GI side effects increase notably at higher doses.
AI-estimated from published studies. Interpret as directional guidance.
Caffeine has a higher evidence score (9.5/10 vs 7.5/10) and wins in 2 of 3 categories.
For athletic performance, Caffeine has a higher relevance score (90 vs 65).
No known interactions between Caffeine and Glycerol have been documented in our database. However, always consult a healthcare provider before combining supplements.