Marine protein, particularly in the form of fish and seafood, is a significant dietary source of omega-3 polyunsaturated fatty acids (PUFAs), such as EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). There is growing scientific evidence suggesting that these omega-3 fatty acids may have a beneficial role in supporting mental health, including the treatment and prevention of depression. Multiple observational studies have found an association between higher fish consumption and a lower prevalence of depressive symptoms. Furthermore, several randomized controlled trials and meta-analyses have indicated that supplementation with marine-derived omega-3s, especially EPA, can have a modest but statistically significant effect in reducing depressive symptoms, particularly in individuals with major depressive disorder.

The proposed mechanisms by which marine protein (through its omega-3 content) may help with depression include anti-inflammatory effects, modulation of neurotransmitter function, and improvement of neuronal membrane fluidity. However, it is important to note that while omega-3s are scientifically investigated, "marine protein" as a whole is not directly studied—rather, it's the specific fatty acid components that are researched. The evidence is stronger for supplementation with concentrated omega-3s than for increased general seafood intake, and the effect size is generally considered modest. Thus, while there is scientific support for the use of marine-derived omega-3s in depression, the evidence does not extend to all forms of marine protein, and it should not be considered a primary or sole treatment.