Soccer's governing body FIFA is alarmed at the number of players taking food supplements and has warned of the risks of failing dope tests by taking non-approved products.
Chief medical officer Jiri Dvorak told FIFA's website that around 35 percent of players at World Cup level were regularly taking food supplements, with that figure rising to almost 50 percent at under-17 and under-20 level.
Dvorak said that many players did not seek medical advice and risked failing doping tests as a result.
"The marketing strategies of the producers of food supplements are influencing the behaviour of footballers and
athletes in general," said Dvorak.
"From different surveys we know that about 60 percent of under-16 athletes in the U.S. are using nutritional supplements daily and all of them believe they will increase their performance.
"It is well established and proven that many of the food supplements are contaminated by prohibited substances such as anabolic steroids and other substances"
FIFA's chief medical officer Jiri Dvorak
"This is definitely not based upon the scientific evidence or literature, which says the opposite."
Dvorak said he was both surprised and alarmed that athletes were not seeking specialist advice.
"The same scientific studies also show that 70 percent of these young athletes do not seek adequate advice from a nutritional specialist physician, they just take it and believe it will improve their performance."
Dvorak also warned that players risked failing doping tests by taking supplements.
"It is well established and proven that many of the food supplements are contaminated by prohibited substances such as anabolic steroids and other substances.
"This is, of course, very dangerous because if the athlete is subject to a doping control test and is regularly using that kind of contaminated supplement, he or she can test positive for doping.
"Therefore, FIFA has issued a serious warning to football players not to take any food supplements that have not been passed by national drug and food administrations."
Dvorak added that there had been reports meat products in some countries, including Mexico and China, contained anabolic steroids.
More than 100 players at last year's under-17 world championship in Mexico failed doping tests due to the presence of the banned substance clenbuterol in contaminated meat.