Athletes shouldn't be able to explain away positive tests by blaming them on dietary supplements or contaminated foodstuffs, says the International Olympic Committee's top anti-doping official.
The chairman of the International Olympic Committee's medical committee Arne Ljungqvist says if athletes eat normally and live normally they won't test positively.
He says of the 5,000 tests carried out at the Beijing Olympics there were about 10 positive tests.
Ljungqvist was speaking in the wake of a warning about supplements last month from Sweden's Sports Council.
In a statement on its website the council warned elite athletes that such products were best avoided as there was no way of knowing what went into them.
Ljungqvist says it's an unregulated market and athletes should to contact their doctor if they felt they needed supplements, as it was the only way to be sure that they didn't fall foul of anti-doping legislation.