It’s important to eat fatty fish several times a week, but many people don’t do that. Therefore, they take fish oil.
In this very good article you write the following: For example, supplementing with vitamin D, fish oil, or multivitamins don’t seem to be beneficial for most people at reducing risk of heart disease, certain types of cancer, or most other conditions outside of certain medical situations.
Why does fish oil not work?
I’m not sure I agree that “it’s important to eat fatty fish several times a week”. Rather, I think the dietary pattern and other factors that allow an individual to eat fish regularly are likely more important than unique benefits of fish itself. Still, I would rate fish as very healthy if forced to rate it.
As far as “why does fish oil not work?” I’m not sure how to answer that exactly. Lots of things don’t work, as evidenced by no significant clinical effect on a specific outcome or set of outcomes in a particular population. For fish oil, supplementing OTC fish oil does not seem to reduce risk of heart disease, diabetes, joint pain, etc.
Prescription fish oil isomers, e.g. Vascepa and similar, do likely offer a benefit for heart disease risk reduction, specifically in those with pre existing disease.
We have a dedicated podcast to this very topic: