NOVELTY - Treating feedstock comprising fatty acid- or triglyceride-containing component comprising at least one contaminant involves contacting feedstock with ion exchange resin to provide treated feedstock having reduced concentration of at least one contaminant.    USE - For treating feedstock comprising fatty acid- or triglyceride-containing component comprising at least one contaminant for preparing hydroprocessed biofuel from a feedstock comprising an animal fat and/or plant oil (all claimed).    ADVANTAGE - The method removes contaminants that are detrimental to the conversion of such feedstocks to hydrocarbons, and especially biofuel fractions such as diesel or aviation biofuels. The contaminants contributing to the presence of trace elements in animal fats or plant oils, as components of feedstocks, hinder the ability to catalytically convert these feedstocks, e.g. by hydroprocessing, to biofuels. The biofuels advantageously exhibit greatly reduced greenhouse gas (GHG) emissions, compared to their petroleum-derived counterparts, based on a lifecycle assessment (LCA) up to and including the ultimate combustion of the fuel composition by the end user. The biofuels have suitable characteristics, in terms of overall makeup (e.g. relatively large, minimally required, amounts of hydrocarbons within a particular boiling range) and in terms of quality (e.g. relatively small, maximally allowed, amounts of thermally unstable compounds such as oxygenates).    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) preparing (M2) a hydroprocessed biofuel from a feedstock comprising an animal fat and/or plant oil involving: contacting the feedstock with a macroreticulated, strong acid cation exchange resin to provide a treated feedstock having a reduced concentration of at least one contaminant selected from Ca, Fe, Mg, Na, P, and K; contacting the treated feedstock with hydrogen and a hydroprocessing catalyst to provide a hydroprocessed product; and separating the hydroprocessed product to recover the hydroprocessed biofuel; and    (2) a biofuel composition made by the method (M2).