Palmitic Acid
http://ajpendo.physiology.org/content/257/6/E937
Oleic acid was a more potent inhibitor than linoleic, stearic, or palmitic acids.
Most potent testosterone inhibitors in Leydig Cells Oleic > Linoleic > Stearic > Palmitic
This paper requires a more detailed read!
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Activiation of testosterone by palmitic and stearic acids
http://www.jbc.org/content/122/2/297.full.pdf
Old paper, but interesting.