Not all forms of dietary phosphorus are equal: an evaluation of postprandial phosphorus concentrations in the plasma of the cat

Phosphorus is present in diets as naturally occurring P from raw materials or added as an inorganic salt. However, little is known about postprandial kinetics of P absorption in cats. Here, we describe several studies quantifying postprandial kinetics following the ingestion of diets of varying composition. Briefly, cats were fed a meal consisting of 50 % of their metabolic energy requirement in a randomised crossover design. A pre-meal baseline blood sample was taken via cephalic catheter and repeated measurements taken regularly up to 6 h post-meal to assess the whole blood ionised Ca, plasma P and parathyroid hormone concentrations. A diet containing 4 center dot 8 g total P/4184 kJ (1000 kcal), 3 center dot 5 g P from sodium dihydrogen phosphate (NaH2PO4)/4184 kJ (1000 kcal) and Ca:P 0 center dot 6 caused a marked increase in plasma P from baseline to a peak of 1 center dot 976 (95% CI 1 center dot 724, 2 center dot 266) mmol/l (P <0 center dot 001), whereas a diet containing 3 center dot 38 g total P/4184 kJ (1000 kcal), no added inorganic P and Ca:P 1 center dot 55 resulted in a postprandial decrease in plasma P (P = 0 center dot 008). Subsequent data indicate that added inorganic P salts in the diet above 0 center dot 5 g P/4184 kJ (1000 kcal) cause an increase in plasma P in cats, while diets below this do not. The data presented here demonstrate that sources of added inorganic P salts cause a temporary postprandial increase in plasma P in a dose-dependent manner, prolonged in diets with Ca:P <1 center dot 0. Dietary P derived from natural food ingredients (e.g. meat or vegetable matter) does not appear to have any effect on postprandial plasma P.