The present disclosure provides low trans-fatty acid fat compositions, methods of hydrogenating unsaturated feedstocks (e.g., oils), and hydrogenation catalyst compositions. One exemplary method involves producing an activated catalyst composition by heating a nickel-based catalyst to a first temperature of at least about 100.degree. C. in the presence of hydrogen and a fat component. An unsaturated feedstock may be contacted with the activated catalyst composition and hydrogenated by sustaining a hydrogenation reaction at a second temperature of no greater than about 70.degree. C. Some specific implementations of the invention permit the production of partially hydrogenated seed oils with low trans-fatty acid contents.