Calcium and phosphorus bioavailability in rats consuming oil from either raw sardines or sardines fried in olive oil

Three diets were prepared containing 8% olive oil (OO), fresh sardine (Clupea pilchardus) oil (SO), and oil from sardines fried in olive oil (FSO), respectively. After in vitro digestion, soluble (dialyzed and nondialyzed) and insoluble Ca and P fractions were determined. In vitro Ca availability tended to be higher with SO, and even more so with FSO, than with OO, while that of P increased only slightly with FSO. Growing rats consumed the diets for 28 days. Food intake and body weight increased with FSO more than with OO, but decreased markedly with SO, due to an imbalance in the n-3/n-6 fatty acid ratio. Absorption efficiencies of Ca and P were higher with SO than with the other diets during days 5-12. Because urinary Ca excretion was also greater with SO, apparent retention of both Ca and P was lower with this diet. With SO, carcass content of Ca and P was low but their concentrations were high. Apparent retention of these minerals and their carcass content were similar or higher with FSO than with OO. Therefore, although availability of Ca and P from raw and fried sardine oil diets was sufficient in vitro, consumption of raw sardine oil as the only dietary fat produced changes in calcium and phosphorus bioavailability, an effect of sardine oil which disappeared after frying in olive oil.