What is the science behind Saw palmetto? How does it actually work?

The main active ingredients responsible for the action of saw palmetto extracts are fatty acids and these are typified by the substance beta-sistosterol which is the marker phytochemical usually used for standardisation.

Saw palmetto extracts have been shown to possess a variety of physiological actions – the one that is most relevant to its use in men with an enlarged prostate is as an inhibitor of 5-alpha-reductase. This review paper will give you more information https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4002402/.

I hope that this is of some help to you.