FDA revoked GRAS status for partially hydrogenated oils (PHOs) as a source of artificial trans fats, effectively prohibiting their use in human food in the US. Imports of hydrogenated fats intended for food use must therefore be fully hydrogenated (essentially zero trans fat) or interesterified rather than partially hydrogenated. Importers should obtain supplier documentation confirming the modification process and trans-fat content before entry.

Oils that are refined, bleached, or deodorized but not chemically modified remain in their source heading (e.g., 1511 for palm oil). Once the oil undergoes a chemical reaction—hydrogenation, interesterification, re-esterification, or elaidinization—it moves to heading 1516. Physical processes such as fractionation or winterization do not trigger reclassification to 1516.