Lead researcher Roel Mocking explains that up to half of patients with depression do not respond to selective serotonin reuptake inhibitor (SSRI) antidepressants. But the new study suggests people with depression who eat fish or take fish oil supplements are more likely to report such drugs are effective, Medical News Today reports.

"We were looking for biological alterations that could explain depression and antidepressant
non-response, so we combined two apparently unrelated measures: metabolism of fatty acids and stress hormone regulation,” he said. “Interestingly, we saw that depressed patients had an altered metabolism of fatty acids, and that this changed metabolism was regulated in a different way by stress hormones."
 

To reach their conclusions, the researchers measured the fatty acid and cortisol (stress hormone) levels of 70 patients with depression, comparing them with 51 healthy adults. The patients with depression were then administered a 20 milligram dose of an SSRI every day for six weeks.
 

Taking measurements of fatty acid and cortisol levels throughout the trial, the researchers found that the depressed patients who did not respond to the antidepressants tended to have abnormal fatty acid metabolism.
 

Because fatty fish is rich in fatty acids, such as omega-3 DHA, the researchers examined the fish intake in the diet of the participants. They found that the participants who ate the least fish tended to have the weakest response to antidepressants, whereas patients who had the most fish in their diet had the strongest response.
 

The team reports that participants who ate fatty fish at least once a week had a 75 percent chance of responding to antidepressants, while participants who never ate fatty fish had only a 23 percent chance of responding to them.