Branched fatty acids are of great interest in the oleochemical industry for many high-end applications due to their interesting physicochemical properties. In the last decades, research has focused mainly on the use of ferrierite (FER) as catalyst for the isomerization of fatty acids into these branched fatty acids. With the use of FER, high yields of branched fatty acids can be obtained. FER is however expensive, and additives are necessary to obtain a high selectivity toward branched fatty acids. In this letter, we focus on the use of ZSM-5, a much cheaper zeolite, which has been extensively studied in the past for other reactions. Five commercial ZSM-5 samples and one hierarchical ZSM-5 sample were tested for the isomerization of fatty acids into branched fatty acids. The results clearly show that the accessibility of Brønsted acid sites is of utmost importance for their catalytic activity. Thanks to the introduction of mesopores in the zeolite crystals of ZSM-5, creating a hierarchical zeolite, a superior catalyst was obtained with a multifold activity increase, without compromising in branched fatty acid selectivity, that is capable of competing against the state-of-the-art FER zeolite.