Glycerol is a sweet liquid that acts like a sponge in your body. When consumed with water or a sports drink, glycerol causes greater fluid retention than drinking water alone. Hyperhydration* before exercise can reduce, delay or eliminate the negative effects of dehydration.
Although there is general agreement that glycerol enhances fluid retention, its effectiveness in enhancing performance is controversial. Some research suggested that taking glycerol with water before exercise enhanced endurance, while other studies found no benefit or advantage over water alone. Glycerol is well-tolerated and has been reported to be safe at an oral dose of 1 gram per kilogram body weight along with water every 6 hours.
Negative side effects reported include: nausea, vomiting, bloating, and light-headedness. Also, there is no information yet available on the effects of taking large volumes of glycerol over a long period of time.
* Hyperhydration is a procedure that introduces extra fluid in the body before activity to prevent dehydration. Hyperhydration can be especially helpful when you work out in the heat.