The Glycerol Controversy
Ellen Coleman, RD, MA, MPH © 2004

In 1997, the United States Olympic Committee announced the addition of glycerol to the banned substances list. The USOC ban is based on glycerol being classified as a diuretic, since in high doses (1 to 2 g per kg) it can be used to "make weight."

Glycerol hyperhydration may also confer an unfair athletic advantage by reducing heat stress. Several studies have suggested that glycerol hyperhydration increases plasma volume and sweat rate, thereby reducing body temperature and improving performance during prolonged exercise in warm weather. Glycerol may provide more substrate energy (glycerol is broken down to dehydroxyacetone).

In one of the first studies, T. Lyons (a graduate student) and colleagues at the University of New Mexico in Albuquerque found that glycerol hyperhydration was more effective than water hyperhydration in reducing the thermal stress of moderate exercise in the heat (see Lyons, 1990). The subjects consumed either 1 g of glycerol per kg along with 21.4 ml of water per kg (glycerol trial) or 21.4 ml of water per kg (water trial). Two and one half hours after fluid ingestion, the subjects exercised on a treadmill at 60% of VO2Max in dry heat (42 degrees C) for two hours. The urine volume prior to exercise was decreased in the glycerol trial compared to the water trial, indicating a glycerol-induced hyperhydration. During exercise in the heat, the glycerol trial caused an elevated sweat rate and lowered body temperature compared to the water trial.

In a later double-blind, crossover study, Paul Montner, M.D. and colleagues at the Veterans Administration Hospital in Albuquerque, New Mexico evaluated the effect of glycerol hyperhydration and carbohydrate oral replacement solution (ORS) on thermoregulation and endurance performance (see Montner, 1996). In the first part of the study, the subjects consumed either 1.2 g of glycerol per kg along with 26 ml of water per kg (glycerol trial) or 26 ml of water per kg (water trial) before exercise. The subjects cycled on two separate days at 65% of VO2Max in a neutral laboratory environment. Glycerol hyperhydration was associated with a significantly longer endurance time (93.8 minutes) and lower heart rate (2.8 beats/minute) compared to water hyperhydration (77.4 minutes).

Next: "Part 2"