Bovine colostrum - highly-concentrated milk that is the first food a cow gives its calf - boosts athletes' immune systems and blood levels of a chemical known as "insulin-like growth factor 1" (IGF-1).
This growth factor is similar to the body-building substances in Human Growth Hormone (HGH), which it is illegal for athletes to use.
The International Olympic Committee is trying to devise tests which will detect whether an athlete has been using HGH, and the whole issue will be considered next February at a specially-convened conference in Lausanne, Switzerland, aimed at unifying the detection of drug abuse in sport.
But finding ways of distinguishing between naturally-occurring substances that may enhance performance and drugs may be complex.
One proposed test for HGH could lead to "clean" athletes who are using bovine colostrum testing positive because of the growth factor levels in their blood.
That would throw the IOC's testing regime into confusion and open it to devastating legal challenges.
That prospect is met with derision by Dr Jennifer Rees, who runs the Glasbury-based company Biomass, the principal distributor of bovine colostrum products in the UK. "It's something that you take as a food, and your body makes what it can from it," she said. "If you ban this, do you stop athletes drinking milk or eating liver? It's only a concentrated form of that."
Tests on bovine colostrum by the University of Jyvaskyla in Finland, published last year in the Journal of Applied Physiology, found that sprinters and jumpers who drank 125ml daily of bovine colostrum in a "blind" trial had higher levels of immune system components and IGF-1 than those on normal milk.
"You can't overdose on it. You'd take two cupfuls a day for hard training," said Dr Rees. "Athletes take it for the benefits to their immune system - they push so hard that they're always liable to get something."
It was first tried by the Finnish cross-country ski team. The the Australian cycling team has also used it.
Tests in 1994 by the IOC confirmed that the Biomass's product contained no banned substances.
However Richard Budgett, director of medical services at the British Olympic Association, said: "The new tests for HGH may go looking for levels of IGF-1. What they will really be looking for is an abnormal picture in terms of the growth factor level. You would have constant testing both during competitions and outside competitions of athletes' blood, and form a picture of the chemicals' levels over time."
But he admitted that any test "has to be 100 per cent certain. You can't have just 95 or 99 per cent. It has to be absolutely solid against a court challenge, because nowadays that's what you'll get if you say someone has failed a test."
The problem in trying to detect HGH abuse is that 25 minutes after it has been injected, its level in the blood has halved.
Furthermore, because the body generates HGH naturally, the injected form and natural forms are indistinguishable. Only by analysing variations in the levels of chemicals associated with HGH could doctors determine whether an athlete was doping.
The IOC is wrestling with a growing problem in trying to police its "banned list" that now includes at least four substances for which no reliable test exists. They are IGF-1 (when taken directly), HGH, insulin (which breaks down sugar into energy stores for muscles) and erythropoietin (EPO), which promotes red blood cell growth.
The discovery of stores of EPO among cycling teams by police during this year's Tour de France triggered a furore. On Saturday there were reports that members of the Parma football team could have been involved in the use of EPOs.
The use of Creatine, another completely legal substance, also provoked controversy when it was disclosed that it was injected into England's footballers during last summer's World Cup.
The substance, which occurs naturally in the body and is classed as a dietary supplement, was used by the hurdler Colin Jackson as an experiment before the 1992 Olympics.
It reduce soreness and muscle stiffness after exercise, and many athletes regard it as a safe and legal alternative to anabolic steroids. Mixed with glucose, it helps muscles work harder and longer, enabling athletes to train more intensively.
Creatine, an animo acid manufactured by the liver, kidney and pancreas, can be bought in chemist shops.
- More about:
- British Cycling Federation
- International Olympic Committee - IOC
- Performance-Enhancing Drugs