In general, foods are grouped together based on phosphorus bioavailability by source as plants, animals, and food additives. 7 Although differences in phosphorus bioavailability between plants and animals have been shown to be clinically relevant, 8 phosphorus bioavailability estimates are largely based on chemical composition and digestibility, which may not reflect the bioavailability in vivo. With this commentary, we attempt to bring attention to this issue byexploring the available data on the proportion of plant-, animal-, and food additive-based phosphorus excreted in urine during controlled-feeding studies.