More than one serious nutritionist has pointed out that the only way to run a true, unbiased nutrition study would be to lock the participants up somewhere that everything they eat and drink could be monitored continuously. People are notorious for fudging their diaries on this subject.
There is a valid point in the OP as well: there are synergistic effects going on. Human metabolism is incredibly complex, and trying to narrow things down to a single component is fraught with complications.
Also to the OP: as has been mentioned in this forum many, many times, PSA is NOT a cancer test. Maintaining a low PSA is not, by definition, keeping cancer from developing or growing. There are common drugs and supplements (finasteride on the drug side, saw palmetto on the supplement side) that are known to depress PSA and have no effect on cancer formation or progression....in fact, while using those products, the person using them should be aware that they could be lulled into an assumption that they are cancer free because of the PSA lowering effects.
Age at Diagnosis: 56
RALP on 2/17/15, BJC St. Louis, Dr. Figenshau
58.5g, G3+4, 20%, 4 quadrants involved
PSA Non-Detect since April, 2015
My Story: www.healingwell.com/community/default.aspx?f=35&m=3300024