The hypercholesterolemic effect of cod protein is reduced in the presence of high dietary calcium

To determine the respective and interactive effects of dietary protein source and calcium level on serum, hepatic, and fecal lipid levels, 48 male New Zealand rabbits were fed purified diets varying in the source of dietary protein, namely casein, cod protein, or soy protein, at an adequate (7 mg Ca/g diet) or a high (14 mg Ca/g diet) concentration of calcium in a 3 x 2 factorial design for 28 days. Dietary proteins interacted with dietary calcium to modulate serum and low density lipoprotein (LDL) cholesterol. When combined with the adequate-calcium diet, code protein induced higher levels of serum and LDL cholesterol than casein and soy protein, induced lower serum and LDL cholesterol than when associated with an adequate concentration of calcium. These results indicate that the hypercholesterolemic effect of cod protein is reduced in the presence of high dietary calcium. Moreover, fecal lipid content was inversely correlated with serum total (p = 0.06) and LDL (p = 0.04) cholesterol in rabbits fed cod protein diets only. An increased formation of insoluble calcium phosphate in the intestine, which may result in lower fat intestinal absorption and serum cholesterol levels, may have been responsible for the decrease in serum and LDL cholesterol in rabbits fed cod protein with high dietary calcium.