Five Mexican soccer players tested positive for clenbuterol earlier this year. The Mexico Football Federation cleared the five, saying contaminated meat caused the positive tests.
The World Anti-Doping Agency last month challenged the Mexico federation's decision and is appealing the case to the Court of Arbitration for Sport in Switzerland.
"We only eat chicken or fish," said fencer Nataly Silva, speaking of the athletes' routine at the government-sponsored training centre. "When we go out we don't eat meat, although we love tacos. When we ask for tacos, we ask for chicken."
Bernardo de la Garza, director of a national agency that handles sport and culture, recently asked athletes not to eat beef.
And Carlos Andrade Garin, president of the Pan American Games organizing committee, has guaranteed that meat will be safe to eat in the athletes' village.
"It is normal after what has happened that people are worried," sprinter Jorge Alonzo said. "I no longer eat meat to avoid giving a positive test. The authorities can do everything possible, but what if you go around the corner and eat a taco and you test positive? Everyone has to take care of themselves."
The Pan American Games open Oct. 14 in Guadalajara, Mexico, with 6,800 athletes competing.
Mexican President Felipe Calderon has acknowledged that contamination with clenbuterol is a problem in the country, where it is used to bulk up livestock.
The Mexico case is WADA's second high-profile challenge to a legal defence of eating tainted meat.
WADA and the International Cycling Union appealed to CAS after 2010 Tour de France winner Alberto Contador blamed contaminated steak for his clenbuterol positive, and was exonerated by the Spanish cycling federation. That case has been scheduled to be heard later this year.