Regular PP readers will be well aware of the antioxidant debate that’s currently raging in sport science circles. In a nutshell, there is some confusion over whether athletes require antioxidant supplements (vitamins C and E, the carotenoids and selenium) to help protect them from the increased damage to cells that inevitably occurs when the body has to process large amounts of oxygen – ie during vigorous exercise. Some studies have indicated that antioxidant supplementation can indeed afford protection, while others have found not only that they offer no protection but that high levels of certain antioxidants can actually increase oxidative damage and even impair performance!

A new study has examined this issue from a completely different perspective by looking at what happens to athletes when they switch from a healthy, antioxidant-rich diet to a more processed antioxidant-poor diet. Seventeen trained athletes underwent two identical exercise tests (a period of submaximal exercise followed by exercise to exhaustion) under two different conditions:

• while consuming their normal healthy diet, which was analysed by the researchers and found (as expected) to be rich in naturally occurring antioxidants;
• after two weeks on a low-antioxidant diet, containing only about a third of the antioxidants present in their normal diet.

After each test, blood samples were taken to see how the diets affected the efficiency of the athletes’ antioxidant defence systems and the amount of circulating isoprostane (a biochemical marker produced in the body as a result of oxidative damage).

The researchers found that on the low antioxidant diet isoprostane concentrations were 38% higher after submaximal exercise, 45% higher after exhaustive exercise and 31% higher one hour post-exercise than they were on the high antioxidant diet. Furthermore, although exercise time to exhaustion was not affected by the diets, the athletes’ rate of perceived exertion was increased on the low antioxidant diet at all exercise intensities. Although measurements of athletes’ antioxidant defence capacities on the two diets weren’t significantly different, they tended to be lower on the low-antioxidant diet.

The researchers concluded that, while there appeared to be no reason to recommend antioxidant supplements to athletes participating in acute high- intensity exercise while consuming naturally antioxidant-rich diets, supplementation might be beneficial for those consuming low-antioxidant diets for prolonged periods of time.

Med Sci Sports Exerc 2005; 37(1): 63-71

Andrew Hamilton