Pre-hydrating with glycerol

Pre-hydrating with glycerol
March 4, 2020 Marisa Michael

How do I pre-hydrate for my race?

Want to learn about a secret the pros use for hydration? Hello, glycerol, nice to meet you!

Glycerol is a substance that allows the body to hold on to a bit more fluid than you normally would. It is called a plasma expander. For this reason, until recently it was a banned substance for competitive athletes by the World Anti-Doping Agency (WADA). In January of 2018, it was officially removed from the banned list.

Why was glycerol banned?

Here’s the backstory: if an athlete is taking a substance that will expand their plasma volume, it would potentially dilute everything else (including illegal substances) in their blood. This might mask drugs or other substances during a doping test. More recent scientific studies have concluded that the dilution and masking effect is minimal and this isn’t a concern. In addition, the average person can consume glycerol on a daily basis unintentionally, which makes it hard to avoid.

Also, glycerol is a natural substance in the body. It is the backbone of triglycerides. Endurance athletes that exercise for long periods of time, like an ultra-marathoner, use fat as part of their fuel source. This fat burning, called lipolysis, can result in elevated plasma glycerol levels. So an athlete in this situation, if tested for glycerol, may test positive. For these reasons, WADA has removed glycerol from the banned substance list.

So can I use glycerol to pre-hydrate?

Well, you don’t have to over-think hydration. Most people in normal circumstances would not need to use glycerol to pre-hydrate. However, an athlete that is about to embark on a really long endurance event, especially one that takes place in heat or humidity, might want to try this. As with all new things, test it first in training! Nothing new on race day EVER!

Also, if you are at the level where you would be considering pre-hydration strategies with glycerol, seek out the help of a sports dietitian. Your hydration and nutrition shouldn’t be a DIY affair. It’s worth the time to get professional guidance.

What is the dosing protocol for glycerol?

The dosed in most studies is 1.2-1.5 g/kg body weight. It is often taken with 500 mL of aspartame-sweetened water (like Crystal Light) to make it taste better. Spreading out the dose over two hours also enhances fluid retention. Athletes stayed well-hydrated after four hours or longer of exercise. Taking 7.5g of salt with the glycerol seemed to decrease urine production (thereby retaining water longer) which was a good thing. In this study, the dosewas 7.5g of salt with 30mL/kg body weight (fat free mass) and 1.4g/kg fat free mass glycerol.

What does glycerol do for me?

Athletes found improved thermoregulatory responses (meaning body temperature regulation) when exercising in the heat, decreased thirst, improved endurance capacity, decreased heart rate, and improved peak power capacity, and improved time to exhaustion compared with a group that pre-hydrated with just water.

What are the cons to using glycerol?

One drawback is that when you have more fluid in your body, you are a bit heavier. Runners in particular like to feel light, and there is a perception that if you are heavier you will go slower. One study looked into this, and the running economy with the runners using glycerol for pre-hydration was the same as the other runners. Another concern is that side-effects can include headaches, dizziness, and nausea.

The take home message is that hyperhydration can be a useful strategy for endurance athletes during a long event, over four or more hours, especially in the heat or humidity. For normal everyday training it’s not needed. Be sure to seek advice from a qualified medical professional to guide you in your hydration strategies. Don’t try to pre-hydrate with glycerol on your own.

What if I want to pre-hydrate without glycerol?

Check out this post on pre-hydration strategies to crush your race! And use our Perfect Hydration for Athletes Course to nail your hydration plan on race day. You might also like our Endurance Fueling course.



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    ~This is general information only and is not nutrition advice. Always check with your healthcare provider before changing any diet, fluid, medication, or supplements.