Proteins from different fish species and different raw materials such as fish fillets and by-products have shown promising cardioprotective effects in rodents and humans, including effects on cholesterol metabolism.

Cardiovascular disease is one of the leading causes of death worldwide and is associated with risk factors such as obesity and dyslipidemia. Primary prevention strategies for cardiovascular disease focus on reducing risk factors by lifestyle modifications and include recommendations from the American Heart Association and the British National Health Service to consume at least two weekly servings of fish.

Dietary Compositions

The amino acid composition differed between the two diets, with a slightly lower content of all indispensable amino acids in the blue whiting BWW diet compared to the control diet.

The glycine content was higher, and the ratios of lysine/arginine and methionine/glycine were lower in the BWW diet than in the control diet, whereas taurine was detected only in the BWW diet.

The fatty acid composition was similar between the diets, except for trace amounts of 20:5 n-3 and 22:6 n-3 in the BWW diet. The dietary cholesterol content was similar between the BWW diet and control diet with 0.23 and 0.24 µmol cholesterol per gram diet, respectively.

The water-soluble fish protein used in the BWW diet consisted of 36.6% peptides with molecular weights larger than 20,000 g/mol, 12.7% peptides with molecular weights in the range of 10,000–20,000 g/mol, 8% peptides with molecular weights in the range of 500–10,000 g/mol.

And 5.5% peptides with molecular weights between 200 g/mol and 500 g/mol, while the peptide fraction smaller than 200 g/mol (comprising free amino acids and miscellaneous water-soluble components absorbing light with a wavelength of 214 nm) amounted to 37.3%.

"We searched for the hypocholesterolemic motifs ALPMH, GGV, GLDIQK, HIRL, IAVPGEVA, IIAEK, LPYPR, PGPL, VAWWMY, VGVI, VGVL, VPDPR, and VYVEELKPTPEGDLEILLQK in the water-soluble protein from blue whiting and of these only GGV was identified," the researchers noted.

Cholesterol in Liver and Feces

Serum concentrations of total cholesterol, cholesteryl ester, LDL cholesterol and HDL cholesterol were significantly lower in the BWW group compared to the control group, while the serum concentration of total bile acids was similar between the two groups.

Cholesterol, HMG-CoA Reductase, and LDL Receptor Concentrations in Liver and Fecal Cholesterol and Bile Acids

The concentration of liver cholesterol was significantly lower in the BWW group compared to the control group. Concomitant with this, the BWW group had significantly lower liver concentrations of HMG-CoA reductase and LDL receptors compared to the control group. A daily fecal output of total cholesterol and bile acids were similar between the two groups.

The concentration of serum total bile acids and fecal excretion of cholesterol and bile acids were similar between the groups. To conclude, the BWW diet led to lower concentrations of serum and liver cholesterol in obese Zucker fa/fa rats, probably due to lower hepatic cholesterol synthesis.