There are reports clenbuterol, a substance banned by the World Anti-Doping Agency (WADA), is being used to increase growth in Mexican livestock, including cattle, lamb, poultry and swine, and could therefore be accidentally eaten by competing athletes.

A number of cases worldwide have shown that illicit administration of clenbuterol to animals destined for food production can result in, if eaten under specific conditions, a positive sample from an athlete.

In humans, the drug is used for performance-enhancement by increasing lean muscle mass and reducing body fat and is classified by WADA under the category of other anabolic agents.

WADA has issued specific warnings about the problem in China and Mexico.

"Unfortunately, anti-doping authorities have no control over agricultural and food safety practices in these countries, and inadvertent ingestion remains an ongoing issue for athletes," the International Paralympic Committee (IPC) said in a statement.

"Both the hotels and the venues where the athletes will be staying will not serve meat (beef or pork).

"However, fish and other low-risk options will be available.

"Athletes must use the utmost care and caution if eating meat whilst travelling abroad, and should be aware of the potential for contamination."

To reduce the risk of unintentionally ingesting clenbuterol through contaminated meat, athletes are being told to choose foods from a reputable source, avoid eating liver or liver-derived products while overseas, and refrain from eating unusual or exotic meat products. 

"Athletes are encouraged to keep a detailed dietary journal whilst travelling to Mexico and China which may be helpful in recalling the details of specific meat ingestion should it be required to assist in results management," the IPC added.

"Under the World Anti-Doping Code, clenbuterol is a non-threshold non-specified substance, meaning that any amount of clenbuterol detected in an athlete urine sample is reported as a positive test.

"Therefore, it is important to note that strict liability dictates an athlete has ultimate responsibility for what is in his/her system, regardless of its origin.

"World Para Powerlifting and World Para Swimming will continue to keep the teams aware of new developments regarding this issue should there are any prior to the World Championships."

The two Championships are being staged from September 30 to October 6  as part of a large Para Sport Festival.

Around 360 of the world’s strongest Para-powerlifters from 65 countries will compete at the Juan de la Barrera Olympic Gymnasium.

More than 550 swimmers from 60 countries are expected at the Francisco Marquez Olympic Swimming Pool.

IPC anti-doping senior manager Vanessa Webb issued a similar warning to athletes regarding the consumption of meat containing clenbuterol shortly before the 2011 Parapan American Games in Mexican city Guadalajara.

The issue was also prevalent at the preceding Pan American Games and increased in magnitude in October 2011 when tests showed that the majority of the players who competed at the FIFA Under-17 World Cup in Mexico earlier that year returned positive doping tests due to contaminated meat.

A total of 19 of the 24 teams had squad members with traces of clenbuterol in their bodies.

The banned anabolic agent was found in 109 of 208 urine samples taken at the tournament, but FIFA and WADA decided not to prosecute in any of the cases because the weight of evidence pointed to meat contamination.

The United States Anti-Doping Agency (USADA) announced earlier this week that athlete Ajee Wilson had tested positive for zeranol and has been stripped of her 800 metres national record.

During its investigation, USADA held discussions with independent experts which explored the use of zeranol as a legal growth promotant in beef cattle in the US.

USADA concluded it was highly unlikely that the presence of zeranol in Wilson’s sample resulted from a source other than contaminated meat.