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.

To examine whether supplementation with low doses of fish or milk proteins would affect glucose regulation and circulating lipid concentrations in overweight healthy adults. 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. Seventy-seven participants were included in the analyses. HER and SAL did not affect glucose and insulin concentrations. COD significantly reduced within-group changes in 90 and 120 min postprandial glucose concentrations but changes were not different from HER and SAL groups. CAS supplementation significantly reduced the area under the curve for glucose concentrations (- 7%), especially when compared to SAL group, and reduced postprandial insulin c-peptide concentration (- 23%). Reductions in acetoacetate (- 24%) and β-hydroxybutyrate (- 29%) serum concentrations in HER group were more prominent compared to SAL and COD groups, with no differences between fish protein groups for α-hydroxybutyrate. Serum concentrations of α-hydroxybutyrate (- 23%), acetoacetate (- 39%) and β-hydroxybutyrate (- 40%) were significantly reduced within CAS group, and the decreases were significantly more pronounced when compared to SAL group. Serum lipid concentrations were not altered in any of the intervention groups. Findings indicate that 2.5 g/day of proteins from fish or milk may be sufficient to improve glucose regulation in overweight adults. The effects were most pronounced after supplementation with proteins from cod, herring and milk, whereas salmon protein did not affect any of the measurements related to glucose regulation. This trial was registered at clinicaltrials.gov as NCT01641055.