Why did Andre Berto test positive for Nandrolone?

The boxer Andre “The Best” Berto tested positive for the steroid Nandrolone. The drug testing was conducted by the Voluntary Anti-Doping Agency (VADA).
 He had to meet Victor Ortiz on June 23, 2012 in Los Angeles. He agreed to submit to random drug testing before the fight. Both “A” and “B” urine samples indicated about intake of the anabolic steroid Nandrolone.
It was already the second time this month, when the VADA tested boxers and caught them taking steroids. The first boxer that tested positive this month due to tests conducted by the VADA was Lamont Peterson. He was scheduled to fight against Amir Khan. It is quite ironically that Peterson requested random blood and urine testing. A carbon isotope ratio test conducted by the VADA manifested that testosterone of exogenous origin was in this fighter’s system certain weeks before the match.
Financial position of certain companies was affected due to tests conducted by the VADA. For example, Golden Boy Promotions lost essential potential profit due to Lamont Peterson’s positives. It was determined by the CEO of the company Richard Schaeffer that the company lost 250, 000 dollars.
The cancelation of the fight between Andre Berto and Victor Ortiz will probably not influence greatly on financial position of certain promotional companies because another boxer will possibly replace Andre Berto and will meet Ortiz.
The boxer Andre Berto didn’t explain what had caused his positives. This boxer hired the attorney Howard Jacobs who would represent and defeat him.
Berto noted that he had never administered steroids. So, he confirmed that he investigated with his attorney what could cause positives for steroids. Andre Berto concluded that he had never cheated; he achieved success in sport due to hard work and dedication.
The attorney Howard Jacobs was hired by numerous other sportspersons that turned out to be victims of contaminated dietary supplements.
It is claimed that since Nandrolone has too long half life and it is detected easily, it is not very popular among doping athletes. But it has been shown many times that several dietary supplements contained the compound nandrolone that led to positives for steroids. But since sometimes not each substance is written on the label, athletes become victims of contaminated dietary supplements.