I'm trying to get information on trans fat. Organisms that need fluidity at low temps are richer in more unsaturated, lower-melting, fatty acids.
Fats are glyceryl triesters of fatty acids.
Hydrogenation saturates the double bonds, alkene back to alkane, and raises the melting point of the products. The double bond oxidatively adds to the nickel metal catalyst. This gives you cis starting materials again. Reverse the reaction, reductive elimination, after a 180 degree rotation of the chain. This gives you trans isomers back.