Unknown to many athletes, supplement use could either be illegal or raise levels of certain active ingredients in their bodies above permitted limits, according to the President of the US Institute of Food Technologists.
Dr Roger Clemens, who is also Professor of Pharmacology and Pharmaceutical Sciences at the University of South Carolina School of Pharmacy, also called for tougher controls on what claims are allowed for supplements targeted at elite athletes and others.
While many supplements are legal in different countries, such as the US, they can be illegal under International Olympic Committee rules, he warned.
Also, until supplement suppliers are forced to provide evidence for their labelling and web site claims, more athletes are likely to damage their health and cause fatal harm by taking short cuts to improved performance rather than using a combination of training and a good nutritional intake, Clemens added.
Clemens was giving the annual Binsted Lecture, held as part of the Institute of Food Science & Technology's (IFST's) Spring Conference last month. His paper was titled: Nutrition's contribution to sport performance: realities and myths. The IFST's conference was on the subject of Nutrition for olympians: nutrition for all.
While controls on doping will be tight at this summer's Olympic games, many athletes will be taking supplements also known as "ergogenic aids" such as caffeine which, unknown to them can sometimes be in quantities that push the boundaries of legality. A number of supplements also have questionable benefits and could even cause long-term health damage, Clemens reported.
He said there was a lack of published peer-reviewed scientific evidence for many of these supplements, from sports drinks and multivitamins to specialist muscle tissue development aids such as creatine. "We really need to advise our athletes what are in the dietary supplements," he added.
"My concern is that many of the things we see on labels and web sites are not substantiated or supported by the evidence or any evidence whatsoever," said Clemens. "They should be required to have the evidence to support it ... It's not likely the FDA [Food and Drug Administration] will take any action on [supplements] until somebody gets hurt."
He added: "We clearly need evidence-based positioning on products that are sold on the market today … hopefully there would be some harmonisation [around the world] ultimately."
Clemens also predicted that over the next decade or so genetic profiling of athletes would become the norm in an attempt to match their fitness programmes and dietary nutrition to their DNA.