The theory that supplements of the carbohydrate metabolite pyruvate can improve endurance during aerobic exercise has been well and truly exploded by a Canadian trial, which examined the effects of increasing dosages of pyruvate in nine recreationally active subjects and seven well-trained cyclists.

Pyruvate has been marketed as a slimming and ergogenic supplement on the basis of studies suggesting that, in combination with another carbohydrate metabolite called dihydroxyacetone, it can enhance weight loss and boost endurance performance. However, only two studies have examined the effects on aerobic endurance in humans and both have used a combined high dosage (100g), which is not only expensive but also tough on the digestive system. Commercially available pyruvate supplements do not contain dihydroxyacetone and are recommended at a considerably lower dosage (3-6g) than those used in scientific studies; yet they are still advertised as a 'scientifically-proven' ergogenic aid.

The scientists responsible for the current trial started from the premise that there was no way pyruvate could affect muscle metabolism during exercise unless its levels were first boosted in the bloodstream. They wanted to find out first whether modest single doses of pyruvate significantly increased blood pyruvate concentrations and, secondly, whether lower dosages available in commercial preparations had any impact on performance in well-trained individuals.

The trial was thus divided into two separate studies:

* In study 1, nine recreationally active people consumed (on three separate occasions) 7, 15 and 25g of pyruvate and were monitored for four hours afterwards to establish any effect on blood metabolites;
* In study 2, seven well-trained cyclists were treated with either 7g of pyruvate or a placebo (dummy preparation) for one week and then cycled at 74-80% of their maximal oxygen consumption until exhaustion to assess the difference in performance times.

Both studies delivered resoundingly negative results. In study 1 pyruvate consumption failed to significantly raise blood pyruvate concentrations and had no effect on selected indices of carbohydrate or fat metabolism. In study 2 there was no difference in performance times between the subjects dosed on pyruvate and those on placebo.

'It is possible,' conclude the researchers, 'that dosages of pyruvate of 25g or greater may elicit an ergogenic effect that was not apparent in the present study.' But there would probably be no point in studying such doses since 'daily consumption of 25g or greater of pyruvate is clearly prohibitive both in terms of cost and potential side effects'.

J Appl Physiol 89: 549-556, 2000

Isabel Walker