A high sodium intake is a major risk factor for raised blood pressure. Consumption of fish fillet is associated with lower blood pressure in humans and other animals, whereas the effects of consuming fish residuals are less explored. To obtain high-quality fishmeal with acceptable sensory properties, the fish residuals may be washed with seawater onboard factory trawlers. This will increase the sodium content in the residuals, and whether this affects blood pressure has not yet been investigated. The primary objective of the present study was to investigate if the increased sodium content in Atlantic cod (Gadus morhua) residuals after washing with saltwater affected the development of high blood pressure in male obese Zucker fa/fa rats which spontaneously develop hypertension. Rats were fed diets containing cod protein powders prepared from unwashed or saltwater-washed backbone or head fractions (n 6/group) as 25% of total protein with the remaining 75% as casein, or casein as the sole protein source (Control group, n 6) for six weeks. Blood pressure was measured on day 0 and 40. The diets containing backbone protein powder, independent of whether this fraction was washed with saltwater or not, attenuated the blood pressure increase compared to the Control group, whereas diets containing washed or unwashed head protein powder did not affect the blood pressure development. To conclude, a diet containing cod backbone protein powder attenuated the blood pressure increase in obese Zucker fa/fa rats, and this effect was not compromised by the higher sodium content in backbones washed with saltwater.

The effects of amount and type of dietary fish proteins on plasma and liver cholesterol concentrations were evaluated in female rats. The isonitrogenous diets used contained 10 g cholesterol/kg and were carefully balanced for residual fat, cholesterol, Ca, Mg and P in the protein preparations. Cod meal, soya-bean protein or casein was incorporated into the diets as the only source of dietary protein a t three levels: either 24,48 or 72 g N/kg diet. Extra protein was added to the diet at the expense of the glucose component. In a second experiment soya-bean protein, casein, cod meal, whiting meal or plaice meal was added to the diet at a level of 24 g N/kg. When compared with casein, cod meal and soya-bean protein decreased plasma and liver cholesterol concentrations. A further cholesterol-lowering effect was achieved by increasing the proportion of either soya-bean protein or cod meal in the diet. Substitution of casein for glucose did not influence plasma and liver cholesterol concentrations. Plaice meal in the diet produced lower group mean plasma cholesterol concentrations than did whiting meal. In rats fed on the diet containing plaice meal, liver cholesterol concentrations were significantly lower than those in their counterparts fed on either cod meal or whiting meal. The present study demonstrates that different fish proteins in the diet have different effects on cholesterol metabolism and that the cholesterol-influencing properties of cod meal can be enhanced by the incorporation of higher proportions of this protein in the diet.