This post is prompted by a new Italian meta-analysis [1] of:
"a total of nine" "eligible studies {that} compared vegetarian, semi- and pesco-vegetarian diets with a non-vegetarian diet."
"Studies were conducted on six cohorts accounting for 686,629 individuals, and ... 1,935 cases of ... prostate cancer"
"None of the analyses showed a significant association of vegetarian diet and a lower risk of ... prostate cancer compared to a non-vegetarian diet."
(This study did not address the more pressing issue of diet & survival.)
[2] (1985 - U.S. - Seventh-Day Adventists)
This small early study reported that:
"Plasma levels of testosterone and estradiol-17 beta were significantly lower in the {vegetarians} than in the omnivores."
"Implications include the possible modification of prostate cancer risk through dietary intervention."
The authors seem to feel that (a) vegetarianism just has to be beneficial & that (b) lower testosterone [T] must protect against PCa. In fact, in matched control studies, PCa cases have lower T on average. Any benefit of a vegetarian diet might be somewhat offset by lower T. (Age itself, which is a PCa risk factor, lowers T by 1-2% per year from the early 30's.)
[3] (1999 - U.K. meta-analysis of 5 studies)
"The absence of a significant association of vegetarianism with prostate cancer mortality in the current analysis does not support the hypothesis that meat may increase the risk for this cancer"
[4] (2016 - Italy - different team than [1])
"Aim of this study was to clarify the association between vegetarian, vegan diets, risk factors for chronic diseases, risk of all-cause mortality, incidence and mortality from cardio-cerebrovascular diseases, total cancer and specific type of cancer (colorectal, breast, prostate and lung), through meta-analysis."
"Eighty-six cross-sectional and 10 cohort prospective studies were included. The overall analysis among cross-sectional studies reported significant reduced levels of body mass index, total cholesterol, LDL-cholesterol, and glucose levels in vegetarians and vegans versus omnivores. With regard to prospective cohort studies, the analysis showed a significant reduced risk of incidence and/or mortality from ischemic heart disease (RR 0.75 ...) and incidence of total cancer (RR 0.92 ...) but not of total cardiovascular and cerebrovascular diseases, all-cause mortality and mortality from cancer."
The Abstract doesn't state how PCa incidence is affected. Interesting that there was no reduction in "all-cause mortality". & apparently, no reduction in PCa mortality.
-Patrick
[1] ncbi.nlm.nih.gov/pubmed/277...
[2] ncbi.nlm.nih.gov/pubmed/401...