Fish consumption as part of a balanced diet has been associated with beneficial health effects, and recent studies have shown that cod intake can improve glucose regulation and insulin sensitivity in both rats and humans.

Improved process technologies have allowed fishing vessels to utilize residuals from cod fillet production (head, backbone, skin, cuttings, and entrails) and convert this to high-quality protein powders for human consumption.

In this double-blind pilot study, 42 healthy overweight or obese adults were randomized to three experimental groups consuming tablets corresponding to 6 g/day of proteins from cod residuals as a presscake meal (Cod-PC), presscake and stickwater meal (Cod-PCW), or placebo tablets (control) for eight weeks. 

Nonesterified fatty acids concentration

The primary outcome of this study changed in metabolites related to glucose regulation in overweight or obese healthy adults after intake of proteins from cod residuals. Cod-PC supplementation decreased postprandial serum nonesterified fatty acids (NEFA) concentration and increased gene expressions of diglyceride acyltransferase 1 and 2 in subcutaneous adipose tissue compared with controls. 

Fasting insulin increased while fasting NEFA and 120-min postprandial glucose decreased within the Cod-PC group, but these changes did not differ from the other groups. In conclusion, supplementation with Cod-PC beneficially affected postprandial serum NEFA concentration compared with the other groups in overweight or obese adults.

Supplementation with Cod-PCW, which contains a higher fraction of water-soluble protein compared to Cod-PC, did not affect serum markers of glucose regulation. In conclusion, supplementation with Cod-PC had a beneficial effect on postprandial NEFA concentration in overweight or obese adults.

The observation that fasting insulin was higher after Cod-PC supplements, whereas fasting glucose was unchanged, suggests reduced insulin sensitivity.  However, since fasting and postprandial NEFA and postprandial 120-min glucose were decreased, this indicates that insulin sensitivity was not reduced after Cod-PC intake.

Supplementation with Cod-PCW, however, which contains a higher fraction of water-soluble protein when compared to Cod-PC, did not lead to changes in the investigated serum markers of glucose regulation.

These findings suggest that consuming presscake meal alone is more advantageous than consuming presscake meal added high amounts of stickwater. As a hypothesis-generating pilot study, the current results should encourage new studies to further elucidate the possible health effects of protein from the cod residual material.

The main findings of the current study are that supplementation with protein from Cod-PC decreased postprandial serum NEFA concentrations and increased gene expressions of DGAT1 and DGAT2 in subcutaneous adipose tissue in overweight or obese adults. 

The current study shows that protein from residual material from cod may affect indicators of human health and could encourage the industry to regard coproducts from fish-fillet production as nutritionally beneficial.