Lifestyle changes are reportedly common following a PCa diagnosis, including a "healthier" diet. I suspect that most would not seek expert advice, because we all "know" what is healthier: more fruits & vegetable, less meat, less fat, more whole grains, & so on. Ask one's doctor for dietary advice, & the familiar boilerplate wording will likely be trotted out. & I almost forgot "drink 8 glasses of water every day".
The Harvard Medical School churns out inoffensive publications, offering health advice. Here is something from March :
"Can adopting a healthier diet help fight prostate cancer? That’s a question men newly diagnosed with prostate cancer often ask their doctors."
"Several studies have shown that in countries where men eat a typical “Western” diet containing a large amount of meat, the incidence of prostate cancer, especially aggressive prostate cancer, is higher than in countries where plant-based foods are a primary part of the diet. Unfortunately, these studies weren’t designed to prove cause and effect. So for now, definitive answers about prostate cancer and diet aren’t yet in — although researchers are actively studying this topic."
"Investigators have launched a federally funded national study to see whether a diet that’s higher in plant-based foods and lower in animal-based foods than the typical Western diet will help control tumor growth in men with early-stage prostate cancer."
"Participants in the Men’s Eating and Living (MEAL) study will try to eat nine servings of fruits and vegetables daily — significantly more than the three to four servings consumed each day by the typical American man — as well as two servings of whole grains and one serving of beans or other legumes."
& so on.
Why am I disgusted? The MEAL intervention study  began in January 2011 (so it isn't news) & ends in June next year. Intermediate findings have not been published. & yet, the Harvard people seem to be promoting the diet. Why? Presumably because the diet seems so healthy. LOL
A sample menu is provided . In addition to the 3 meals, we get 3 snacks. More food than I could eat in a day, but without the snacks, how could we get our quota of fruit?
The MEALS study involves men on active surveillance, & you can't safely extrapolate findings from that kind of study to metastatic disease.
What we do have (in PubMed) is a bunch of epidemiological studies that looked at fruit & PCa risk, & an intervention study, like MEALS, in men without PCa :
 (2000) "No associations were found between fruit intake and prostate cancer risk."
 (2000) "Intake ... of fruits was not related to risk"
 (2002) "Dietary intervention over a 4-year period with reduced fat and increased consumption of fruits, vegetables, and fiber has no impact on serum PSA levels in men. The study also offers no evidence that this dietary intervention over a 4-year period affects the incidence of prostate cancer during the 4 years."
 (2004) "No significant associations between fruit ... consumption and prostate cancer risk were observed." Huge study: 130,544 men in 7 countries
 (2004) This study identified 3 dietary patterns:
"prostate cancer risk was not associated with the vegetable-fruit or red meat-starch pattern, but higher intake of the Southern pattern showed a reduction in risk"
"although the red meat-starch pattern was not associated with prostate cancer, intermediate intake of the vegetable-fruit pattern showed a slight elevation of risk [RR, 1.5 ...]"
 (2008) (Australian) "A decreased prostate cancer risk was observed with increasing intakes of vitamin C-rich vegetables, including bell peppers and broccoli. Fruit, other vegetables and vitamin A intakes did not appear to be strong factors in the development of prostate cancer in this study."
 (2010) (Japanese) "no association was observed for intake of either fruits or vegetables (total or any subtype) with localized or advanced prostate cancer"
 (2014) (European) "no clear indication that the risk for prostate cancer is related to intakes of ... fruit"
Another big study: 150,000 men in eight European countries.
No doubt the gurus will continue to advise us that fruits belong in a PCa diet, but a null effect on PCa risk doesn't give me much hope for the MEALS study, or for any effect on metastatic PCa.
A common problem with epidemiological dietary studies is a lack of nuance. Corn oil & lard becomes "fats"; strawberries & bananas are "fruits", & so on. Can't I find something good to say about fruit? Yes - but very little:
 (1995) Giovannucci's study that began the lycopene industry. Most seemed to ignore the reference to strawberries. Rich in fisetin.
Pomegranate studies look interesting, but whole pomegranates aren't likely to show up in epidemiological or intervention studies. The two Pantuck studies are inconsistent:
 (2006) Juice. "Mean PSA doubling time significantly increased with treatment from a mean of 15 months at baseline to 54 months posttreatment"
 (2015) Extract. A PSADT "increase from 12.9 months at baseline to 14.5 months". The placebo group did better.