Glycerol is a substance that allows for more effective hydration. Typically used before events, glycerol improves the body’s retention of water by reducing urinary output after consuming fluids.
As a supplement it has not received a lot of attention by competitive athletes and their coaches as it was previously banned by the World Anti-Doping Agency (WADA).
However, that changed in 2018 when WADA removed it from its banned substances list.
What is Glycerol?
Glycerol is a 3-carbon sugar alcohol that forms the backbone of triglycerides.
This fact is actually really relevant to why it was removed from the WADA banned substances list.
Endurance athletes that exercise for long periods of time such as Ironman triathletes and ultra-endurance runners use fat as a fuel source.
During this type of exercise, carbohydrates, which the body can only store a limited amount of, will often run out. The athlete’s body will then be forced to increase the percentage of utilisation of fat stores for the energy required to complete the training or event.
To be used as energy, triglycerides undergo lipolysis. Basically, the triglycerides are broken down subsequently resulting in a higher blood level of glycerol.
So an athlete who is using fat as their predominant fuel source in an event may actually test positive for glycerol even if they were not supplementing the substance.
As such, WADA decided to remove it as a banned substance.
Glycerol is naturally occurring in many foods but is also used as an emulsifier, humectant, sweetener, low-energy filler or thickening agent, and preservative by the food industry.
Interestingly, it is also a common ingredient in non-food items such as soaps, pharmaceuticals, cosmetics and skincare.
How Does Glycerol Enhance Hydration?
Glycerol consumed orally, typically as part of a beverage, creates an osmotic gradient that favours fluid retention.
This means that the kidneys, which are responsible for fluid excretion and maintaining fluid and electrolyte balance, will reabsorb more water as the water passes through them.
Thereby reducing urinary output and allowing the body to be more hydrated than what is normal (i.e. hyperhydrated).
Studies have shown that up to 1L of extra body water is achievable through sufficient glycerol supplementation.
The effects of glycerol supplementation last for up to 4-hours.
Combining Glycerol & Sodium For Hyperhydration
Using sodium and other electrolytes as a way to improve hydration has been a critical part of sports nutrition for a long time.
Unlike glycerol, sodium has never been banned by WADA so it has been the go-to hydration agent to assist with fluid retention.
However, now that athletes can use glycerol, both sodium and glycerol can be combined to maximise pre-event hydration.
The following diagram illustrates the fluid retention achieved through three common hyperhydration strategies.
- WIH = Water induced hyperhydration
- GIH = Glycerol induced hyperhydration
- SIH = Sodium induced hyperhydration
- G+SIH = glycerol & sodium-induced hyperhydration
As you can see both sodium and glycerol assist significantly with water retention. But when combined there is 72% more water retention than consuming water alone.
This could be a huge benefit for athletes who struggle to maintain sufficient hydration when starting in a euhydrated state (normally hydrated).
Why Would You Want To Be Hyperhydrated?
Research shows that losing just 2% or more of your body weight through fluid losses can have a significant impact on performance.
There are a lot of reasons why an athlete may lose this much fluid including,
- Being unable to replace fluids adequately during an event due to issues with tolerability and/or accessibility to fluids
- Particularly hot and humid conditions causing a very high sweat rate
- An athlete has an individually high sweat rate, above what is expected
Whilst you can work on tolerating a higher fluid intake during exercise, many of these issues cannot be helped. Especially in regards to environmental conditions and accessibility to fluids.
In these cases, hyperhydration could be very beneficial to an athlete and prevent them from reaching a level of dehydration that would be detrimental to their performance.
Essentially, athletes would be able to tolerate higher fluid losses without a reduction in performance.
What Does The Research Say?
Glycerol & Cardiovascular benefits
Eight individual studies looking at pre-exercise glycerol hyperhydration showed positive benefits in relation to cardiovascular function.
These benefits included reductions in exercising heart rate, increased cardiac filling and stroke volume, and better maintenance of plasma volume.
In other words, glycerol induced hyperhydration may reduce the strain on the cardiovascular system during exercise.
This makes sense considering that one of the downfalls of being dehydrated is that the heart has to work harder to pump blood around the body. Leading to a higher heart rate which can only be sustained for short periods of time.
Theoretically, the reduced cardiovascular strain allows increased oxygen and nutrient delivery to working muscles as well as enhanced removal of waste products.
Glycerol & Thermoregulation
Another benefit of glycerol induced hyperhydration appears to be its thermoregulatory effects.
Research has shown that sweat rate actually increases 14-50% when an athlete is hyper-hydrated with glycerol. Such increases, in theory, should result in better evaporative cooling and reduced core temperature.
Furthermore, some studies have indicated that a reduction in temperature is seen with glycerol supplementation prior to exercise.
The largest reduction in temperature seen in current literature was accompanied by a 33% increase in sweat rate.
Contrastingly, an increase in sweat rate does not always equal better thermoregulation. Another study showing a 50% increase in sweat rate following glycerol-induced hyper-hydration did not show reductions in core temperature.
Although researchers believe this may have been due to a very high humidity in that particular study.
Glycerol & Perceived Exertion
Undertaking long-duration, high-intensity exercise in the heat induces both severe physiological stress and psychological stress.
This psychological stress is directly correlated to the rate of perceived exertion (RPE).
If an athlete feels like they are working really hard, they are likely to struggle with the mental aspect of performance more.
Whilst research is mixed, the majority of studies investigating glycerol supplementation and RPE have shown that athletes are able to maintain a higher work rate without feeling like they are actually working any harder.
This is likely due to the reduction in dehydration as well as the cardiovascular and thermoregulatory functions of glycerol hyperhydration.
Glycerol & Getting a Better “Pump”
Whilst traditionally glycerol has been used mostly in endurance sports where dehydration is a common problem, the supplement industry has found another reason to use it.
Given that glycerol increases the vascular movement of water it can actually be used to get a more pronounced “pump” when strength training.
The jury is still out on whether a good pump leads to actual increases in strength and muscle mass but for many gym-goers, the satisfying feeling of a good pump is all they are after.
What makes glycerol an intriguing pump booster is that it takes a different route to most effective pump-inducing ingredients.
Most pump boosters increase nitric oxide production which helps increase vasodilation.
Glycerol, on the other hand, increases vascularity by drawing additional water into the muscles. This means that it can work alongside and in combination with more typical pump boosters.
How To Use Glycerol
There are several ways that glycerol supplementation can be incorporated into an athlete’s hydration plan.
The most common is pre-event hyperhydration as previously discussed.
However, you can also use glycerol during and after exercise to assist with maintaining adequate hydration levels and re-hydrating quickly post-event.
Many athletes complete multiple, intense training sessions on a daily basis or are expected to compete at events where they need to repeat maximal performance efforts in a single day.
When there is little time for recovery between training sessions or events, using glycerol to rehydrate can be an effective strategy.
Rehydration is a vital component of recovery but it can take time to effectively rehydrate after an event. Supplementing with glycerol can speed up this process by reducing the urinary output of fluids.
In regards to using glycerol during exercise, it is likely unnecessary in most cases where hyperhydration prior to the event has occurred.
But in some circumstances where fluid availability is low, for example, only being able to drink during a half time break, it could make sense to use a glycerol containing beverage.
You will basically be getting the most bang for your buck with the limited amount of fluids you are able to drink.
Another reason would be in circumstances where the event time is particularly long like a full-length ironman or multi-day endurance event.
Nonetheless, drinking and retaining fluid at a greater rate than required to replace sweat losses is not recommended. Meaning that you should not gain weight during an event.
This could potentially happen if you were to hyper hydrate prior to the event and also supplement with glycerol during. Particularly if your fluid intake is adequate.
Not a lot of research has been done into glycerol supplementation during an event without hyperhydration pre-event. It is typically recommended that pre-event hyperhydration is the more appropriate option since you need to have a fairly high fluid intake with glycerol, which may not be possible during exercise.
You will also want to wait at least 30 minutes after finishing the recommended fluid intake with glycerol to allow for some urinary excretion.
Doing it during the event may lead to having to stop to urinate which is often not ideal.
The below guidelines published in the peer-reviewed journal Nutrition Reviews provides a great summary on how to use glycerol for hydration in sport. Note they have been altered to make them easier to interpret.
|Purpose of glycerol use||Guideline|
|Pre-exercise hyperhydration||• Only undertake a pre-exercise glycerol hyperhydration protocol if the exercise is likely to induce a reduction in body weight (BW) of >2%.|
|• Consume a glycerol dose of 1.2g/kg of body weight with 26mL/kg of fluid. |
|EXAMPLE: 75kg athlete would consume 90g of glycerol added to 2L of fluids over the course of 60 minutes at least 30 minutes prior to exercise/event. Ideally, fluids would be a carbohydrate-electrolyte beverage but can also be water. A set of calibrated scales should be used to measure glycerol dose.|
|Glycerol rehydration during exercise||• If pre-exercise hyperhydration has taken place, you can consume 0.125g/kg BW of glycerol with 5mL/kg BW worth of fluids.|
EXAMPLE: 75kg athlete would consume 10g in 350-400mls of fluids
|• Drinking fluid at a rate greater than that required to replace sweat loss (leading to a net weight gain during exercise) should be avoided. Therefore, if an athlete is hyperhydrated before exercise lasting 75 min or less, very little fluid would be needed during exercise under most conditions, and the consumption of glycerol with any fluid is not recommended.|
|• If no pre-exercise hyperhydration has taken place, then a larger dose of glycerol with fluid during exercise is warranted. Therefore, we recommend athletes consume 0.4g/kg BW glycerol with fluid during each of the first 4h of exercise. |
EXAMPLE: 75kg athlete would consume 30g of glycerol each hour for the first 4-hours of the event with the amount of fluid that can be tolerated
|Glycerol rehydration post-exercise||•Glycerol use post-exercise should only be used when rehydration has to occur quickly. Consume 1.5L of fluid for each 1 kg of weight loss.|
|• Add 1.0g/kg BW of glycerol to each 1.5L of fluid consumed.|
EXAMPLE: 75kg athlete who had 1L of sweat losses would consume 1.5L of fluids with 115g of glycerol
|• If there is a long duration between successive exercise bouts, then rehydrate with water and meals and follow the pre-exercise hyperhydration recommendations before the next exercise session.|
|General recommendations||• Try using glycerol in training before attempting to use it during competition.|
|• If side effects are encountered, discontinue use or try to personalize the above recommendations by consuming a small dose of glycerol|
Potential Side Effects of Glycerol
Glycerol is generally very well tolerated. Even more so than sodium supplementation. In hydration research, only three of twenty-eight studies reported side effects from glycerol supplementation. And even so, only 1-4 participants from each study experienced side effects.
Although unlikely, it is possible for glycerol to result in:
- Gastrointetinal discomfort
- A laxative effect
- Body mass gain impairing performance
That is why it should always be tested in a training setting prior to use for an event.
Another caveat or potential drawback of glycerol use would be the calories provided by glycerol. Glycerin is a sugar alcohol that contains 4.32kcals per gram. That is slightly more than the calories provided by a gram of carbohydrates or protein.
Using the example of the 75kg athlete using glycerol to hyper hydrate prior to an event, they would be consuming almost 400kcals through the glycerol alone using 90g in their fluids. If they were also using a carbohydrate-rich fluid, they may be getting 800-1000kcals just by using this protocol.
If this protocol was being used in an event every couple of months, the additional calories would likely not be a concern. However, if an athlete was to use this regularly in training it may lead to unwanted weight gain over time.
Where Do You Get Glycerol?
“Glycerol can be purchased in Australia from supermarkets, pharmacies, and chemists under the name of glycerine. It should be noted that the description on the bottle can cause confusion, as it is listed for use as an emollient to soften roughened skin. Glycerol is safe to ingest.” – Australian Institute of Sport
Hydration is one of the key puzzle pieces of optimal performance. Even fluid losses of more than just 2% of a person’s body weight have been shown to have significant detrimental impacts on performance.
There are many circumstances in which athletes, even with a thorough hydration plan and pre-event hydration, cannot replace enough of their fluid losses during an event.
Its in these circumstances, glycerol can be a particularly useful supplement. It allows athletes to become hyperhydrated and therefore sustain larger fluid losses before experiencing decreases in performance output.
Outside of pre-event hyperhydration, glycerol can also be used to maintain hydration during an event (typically ultra-endurance events), quickly and effectively re-hydrate between events where the window for recovery is small and also to provide a better ‘pump’ when strength training.
Glycerol can be found in your local chemist and supermarkets under the name, Glycerine. Refer to the use and dosage guidelines above if you want to trial glycerol supplementation for yourself.