Could chemicals used to pump up beef cattle turn up in a top athlete's body during competition? Alberto Contador would have you believe so.
Three-time Tour de France champion Contador said last week that his positive doping test was the result of eating bad beef -- specifically a tender piece of filet mignon that one of his associates picked up in a small Spanish town just across the border from where Contador and the rest of his teammates were staying last July 20.
Authorities with the International Cycling Union say that Contador flunked a urine test that day for Clembuterol, a hormone used by athletes to boost performance, by livestock owners to boost muscle mass and by asthma patients to help them breathe better. Now Contador -- a Spanish cycling hero -- has been suspended from racing.
Does his explanation pass the smell test? And, more broadly, do the chemicals used on meat harm consumers?
Lynn Goldman is Dean of the School of Public Health at George Washington University and former EPA assistant administrator for toxic substances. She acknowledges the mantra of scientists when it comes to harmful substances: The dose makes the poison.
"If you're eating a small piece of an animal," Goldman said, "you may not get enough to make it pharmacologically significant."
Goldman says that hormones given to cows are identical to ones produced by their own bodies. The result is that it is difficult to detect the extra amount in the meat or milk for consumed by humans.
"The real controversy is over the health of the animal, not over people drinking the milk," Goldman said.
The European Union has banned farmers from using any growth hormones. Still, there have been cases of people getting sick from eating calf liver contaminated with Clembuterol in both Spain, Italy and Portugal in the 1990s, and more recently in China.
The U.S. Department of Agriculture allows Clembuterol in show horses, but not beef cattle. About 85 percent of U.S. beef receive some kind of growth hormone, such as estrogen, testosterone or estradiol, according to Michael Baker, agriculture specialist at Cornell University's animal science department.
"It's a widely used technology. It reduces fat and lean tissue," Baker said about growth hormones.
Top athletes are also looking for efficiency, fat reduction and lean muscle tissue. In fact, the "bad beef" defense isn't novel.
An Italian female mountain biker blamed her positive nandralone test in 1997 on eating Belgian beef. A German ping pong champion said his positive Clembuterol test last month was from bad Chinese meat.
As for Contador, he also said that the tiny amounts of the chemical wouldn't have given him any kind of a boost.
Goldman disagrees. "The fact is because this is a substance which shouldn't be there at all," she said.
On Friday, the French sports daily L'Equipe reported that Contador's blood sample also contained small amounts of plastic. That suggests that Contador may have used a plastic bag of his own blood in an transfusion -- a illegal practice well-known among endurance athletes.
If convicted, Contador faces a two-year ban and loss of the maillot jaune, the yellow jersey given to the Tour's winner each year.