Caloric restriction is one of the known triggers for porphyria attacks because it increases the demand for heme and upregulates the first enzyme in heme biosynthesis, ALA synthase-1 (ALAS1), which thus leads to a buildup of ALA and PBG since these precursors cannot be adequately utilized by the defective PBG-deaminase. Here, ALAS1 is linked to porphyria.