Shelby Houlihan is the US record holder in the 1500m and 5,000mAmerican middle distance runner Shelby Houlihan has been banned from athletics for four years after testing positive for a prohibited substance – which she blamed on a burrito.The 28-year-old says she was told in January the anabolic steroid nandrolone had been found in a doping sample.Olympian Houlihan said it may have come from eating a pork burrito, which she said could lead to a false positive for nandrolone, the night before her test.She has denied ever doping.The Athletics Integrity Unit confirmed she was handed the four-year ban by the Court of Arbitration for Sport on Friday, backdated to 14 January.”I feel completely devastated, lost, broken, angry, confused and betrayed by the very sport that I’ve loved and poured myself into,” Houlihan said in a statement on social mediaexternal-link. “I want to be very clear. I have never taken any performance enhancing substances.”Houlihan, the US record holder in the 1500m and 5,000m, said she had “never even heard” of nandrolone, which can help to increase muscle mass.”I have since learned that it has long been understood by Wada (World Anti-Doping Agency) that eating pork can lead to a false positive for nandrolone, since certain types of pigs produce it naturally in high amounts. Pig organ meat (offal) has the highest levels of nandrolone,” she said.”In the following five days after being notified, I put together a food log of everything that I consumed the week of that December 15th test. “We concluded that the most likely explanation was a burrito purchased and consumed approximately 10 hours before that drug test from an authentic Mexican food truck that serves pig offal near my house in Beaverton, Oregon. “I notified the AIU that I believed this was the source.”She added: “I did everything I could to prove my innocence. I passed a polygraph test. I had my hair sampled by one of the world’s foremost toxicologists.”Wada agreed that test proved that there was no build up of this substance in my body, which there would have been if I were taking it regularly.”The four-year ban will see Houlihan, who competed at the Rio Olympics in 2016, miss both the Tokyo 2020 and Paris 2024 Games.