Seasonal changes in phosphorus content of fish tissue as they relate to diets of renal patients.

OBJECTIVE To investigate seasonal variations in tissue phosphorus (P) levels, P to protein ratio, and P to omega-3 fatty acid (ω3-FA) ratio in 2 species of fish that are commonly consumed in Lebanon. We aim to determine suitability for dietary management of renal patients. DESIGN AND SETTING Siganus rivulatus (rabbitfish) and Diplodus sargus (white seabream) were caught in traps off the coast of Beirut and transported on ice to the laboratory during various seasons. Fillets of fish were removed, dried to constant weight at 95°C, finely ground, and stored at -20°C. Protein, P, P to protein ratio, and P to ω3-FA ratio were determined. RESULTS Compared with white seabream (carnivore), rabbitfish (algaevore) had a significantly lower mean P content (±SE) (895 ± 32 mg/100 g vs. 1,132 ± 23 mg/100 g; P < .0001), a significantly lower P to protein ratio (±SE) (10.35 ± 0.39 vs. 13.15 ± 0.34 mg P/g of protein; P < .001), and a significantly lower P to ω3-FA ratio (±SE) (2.81 ± 0.29 vs. 5.93 ± 1.05 g of ω3-FA/g of P; P < .005). P content in flesh of both species varied significantly with season (P < .0001). Rabbitfish P content was least in August and greatest in June (P < .05), whereas white seabream P content was greatest in April and least in June (P < .05). Rabbitfish muscle P to protein ratio and P to ω3-FA ratio was least in August, with a significantly greater P to ω3-FA ratio during the rest of the year. White seabream exhibited wider seasonal variation in P to protein ratio and P to ω3-FA ratio as compared with rabbitfish. CONCLUSION Because of differences and seasonal variations in P levels that exist among fish species, renal dietitians may need to identify the seasonal proximate composition of individual fish species in various habitats and formulate dietary regimens accordingly. Such advice notwithstanding, oily marine fish remain a healthy food choice for dialysis patients if the fillet is consumed without bones.