There’s little question that fish contain environmental pollutants such as mercury and PCBs with, generally, bigger fish such as shark and tuna containing more and smaller fish like sardines containing less. That’s been common knowledge between health researchers for a while now. The real question is whether that translates into any of the major degenerative diseases in people (such as cancer or diabetes).
Well, sadly, in the case of diabetes it does appear to be the case.
Here’s a great video by Dr. Michael Greger summarizing the science between diabetes risk and fish consumption:
As he mentioned in the video, besides the pollutants, the causal link could also very well be the oxidative stress causing n-3 fatty acid content of the fish. That obviously goes against the mainstream opinion on diet but one can certainly find smart people that would support that notion and as far as I’ve seen the research on fish oil seems to be quite mixed.