Effects of low doses of fish and milk proteins on glucose regulation and markers of insulin sensitivity in overweight adults: a randomised, double blind study.

Purpose: To examine whether supplementation with low doses of fish or milk proteins would affect glucose regulation and circulating lipid concentrations in overweight healthy adults.

Methods: Ninety-three overweight adults were assigned to receive 2.5 g protein/day from herring (HER), salmon (SAL), cod (COD) or milk (CAS, a casein-whey mixture as positive control) as tablets for 8 weeks.

Hydrolyzed proteins from herring and salmon rest raw material contain peptide motifs with angiotensin-I converting enzyme inhibitors and resulted in lower urine concentrations of protein, cystatin C and glucose when fed to obese Zucker fa/fa rats.

The use of angiotensin-I converting enzyme (ACE) inhibitors is a common strategy for treating kidney disease. Several amino acid sequences with ACE inhibiting activity are identified in filet and rest raw material from various species of fish, and fish protein hydrolysates could be of interest for possible treatment or prevention of kidney disease. Therefore, we hypothesized that protein hydrolysates from rest raw material from herring and salmon contained ACE inhibiting motifs, and could beneficially affect typical markers for kidney function in an obesity rat model prone to developing renal failure.

Dietary fish protein hydrolysates containing bioactive motifs affect serum and adipose tissue fatty acid compositions, serum lipids, postprandial glucose regulation and growth in obese Zucker fa/fa rats.

The world's fisheries and aquaculture industries produce vast amounts of protein-containing by-products that can be enzymatically hydrolysed to smaller peptides and possibly be used as additives to functional foods and nutraceuticals targeted for patients with obesity-related metabolic disorders. To investigate the effects of fish protein hydrolysates on markers of metabolic disorders, obese Zucker fa/fa rats consumed diets with 75 % of protein from casein/whey (CAS) and 25 % from herring (HER) or salmon (SAL) protein hydrolysate from rest raw material, or 100 % protein from CAS for 4 weeks. The fatty acid compositions were similar in the experimental diets, and none of them contained any long-chain n-3 PUFA.

A low dietary intake of cod protein is sufficient to increase growth, improve serum and tissue fatty acid compositions, and lower serum postprandial glucose and fasting non-esterified fatty acid concentrations in obese Zucker fa/fa rats.

Purpose: Studies in rats suggest that fish proteins may improve lipid and glucose regulation and could thus be a potential tool in the treatment of obesity-related comorbidities. To date, all published rat studies on dietary fish protein have been designed with 50 or 100% of dietary proteins from fish. As it is not common, nor advised, to consume fish as the only protein source in a healthy diet, mechanistic studies on the effects of diets with low dose fish proteins are needed.