How we rate
“Strong” = several concordant meta-analyses or systematic reviews. “Moderate” = one synthesis, or several controlled trials. “Limited” = early trials only. The rating is about the quality of the studies, not about how useful the supplement is.
Glycerol
Taken with plenty of water before exercise, glycerol causes more fluid to be retained. Older trials find slightly more endurance, recent trials find nothing anymore, even in the heat.
Benefits
- Pre-exercise water retention: compared to the same amount of water alone, it causes an extra 7.7 mL of fluid per kilo of body weight to be retained (meta-analysis).
- Half-marathon in the heat: in 13 runners, glycerol and salt caused an extra 1189 mL of fluid to be retained and plasma volume to increase by 9.0%, without changing the time.
- Endurance: in the meta-analysis, endurance performance improves by 2.62%, but based on only 4 studies.
- Cycling to exhaustion: in a 1996 trial, 93.8 minutes instead of 77.4, and 123.4 instead of 99.0 with a sugary drink during exercise, with a slower heart rate by 2.8 to 4.4 beats per minute.
- Cycling time trial in the heat: in 8 cyclists, 5% more work in the free part of the effort.
- Triathlon in the heat: in 10 triathletes, the time only lengthened by 1 min 47 s between a tepid day and a hot day, compared to 11 min 40 s under placebo.
Precautions
Rare side effects: nausea, digestive discomfort, dizziness, and headaches. Anti-doping: the World Anti-Doping Agency added it in 2010 to its list of prohibited substances, as a masking agent; if you are tested, check the current list. Detection: one review notes that a dose much lower than that of the trials can already be found in the urine. Extra weight: with creatine for 7 days, runners gained 0.90 kg, mostly water, without losing running economy. Limitations: recent trials find nothing: neither on a half-marathon, nor on 5 km in the heat, nor cycling in the heat in 2025, nor in high-level race walkers. No better than water in other trials: 1 hour of cycling in the heat, 2 hours of cycling at 25 °C while drinking during exercise, tennis tests. If you drink enough during exercise, one review finds no advantage on body temperature, sweat, or heart rate. Reviews consider performance gains inconsistent and call for more data. Trials are small (6 to 17 people), almost all in endurance; none in bodybuilding.
Recommended dosage
1 to 1.2 g per kilo of body weight, diluted in 21 to 26 mL of fluid per kilo, before exercise.
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How to take it
- Before exercise: a review advises 1.2 g per kilo in 26 mL of fluid per kilo, drunk over 60 minutes and finished 30 minutes before the start.
- Always with plenty of fluid: it is the water drunk with it that glycerol helps to retain; on its own, it is useless.
- With salt: in 15 young men, salt and glycerol together caused 1435 mL to be retained, compared to 729 mL with glycerol alone.
- Salt alone does better: in 17 men, it caused 1144 mL to be retained compared to 795 mL with glycerol.
- During and after exercise: the review suggests 0.125 g per kilo during, and 1 g per kilo in every 1.5 L drunk after, with less data.
- To rehydrate quickly: in 7 wrestlers, a glycerol drink did not rehydrate better than water nor restore power.
Did you know?
In 2010, the World Anti-Doping Agency added glycerol to its list of prohibited substances: the water it causes to be retained dilutes the blood, to the point of potentially masking doping.
What the studies say
A meta-analysis concludes that glycerol-induced hyperhydration increases fluid retention more effectively than water alone. This strategy is also associated with an improvement in endurance performance of approximately 2.62%. However, more data are needed for definitive conclusions on its ergogenic role.
Goulet ED, Aubertin-Leheudre M, Plante GE, Dionne IJ. — International journal of sport nutrition and exercise metabolism (2007) — View the source study
Pairs well with
For information only: not a substitute for medical advice. Dietary supplements are not a replacement for a varied, balanced diet. Learn more