A large study from 2014 by Nimptsch et al found a strong inverse correlation between intake of vitamin K2 and prostate cancer [2]. Dairy foods with K2 had the most effect (K2 is soluble in butterfat).
Vitamin K2 helps remove calcium from the elastin in artery and vein walls, reducing their stiffness. Donaldson hypothesizes that K2 improves venous flow, and hence might reduce the varicoceles that lead to too much free testosterone getting to the prostate and causing enlargement.
So eat more grass-fed butter, or take a K2 supplement. At worst, you might also improve your bone strength. At best, men might prevent prostate cancer.
1: DOI: 10.1016/j.mehy.2014.12.028
2: DOI: 10.1093/ajcn/87.4.985