Its not the presence of fish, it is the absence of stuff
I have not researched this area thoroughly enough, but it would also make sense that it is the absence of other things in the diet of those who choose to eat more fish, rather than the presence of fish by itself that might contribute to “improvements” in things like triglicerides in patients who choose to adhere to a cerain diet or take a supplement.
Once again, this is just an opinion, but it seems to me that patients who choose to modify their lifestyle in any way benefit tremendously from whatever the food additive/vitamin/supplement they choose to add to their diet (Especially if they also exercise, lose weight, and eat less in general). I am not aware of any adverse effects of consuming fish oil, omega 3 or anything in that category, but I would rather recommend a person walks a little more and eats a little less than take any form of supplement.
Here are a few exaples of quotes from abstracts that I have read on the subject:
“Because of the suboptimal quality of the studies included into the meta-analysis and the absence of data in patients receiving statins, these results do not justify adding fish oils systematically to the heavy pharmaceutical assortment already recommended in CHD patients.”- Am J Prev Med. 2005 Nov;29(4):347-52.
“This meta-analysis shows that consumption of ALA might reduce heart disease mortality. However, the association between high intake of ALA and prostate cancer is of concern and warrants further study.” -J Nutr. 2004 Apr;134(4):919-22.
And probably the most famous of these meta-analyses—-
“There was no difference in summary estimates between dietary and non-dietary interventions of n-3 polyunsaturated fatty acids for all endpoints. CONCLUSION: This meta-analysis suggests that dietary and non-dietary intake of n-3 polyunsaturated fatty acids reduces overall mortality, mortality due to myocardial infarction, and sudden death in patients with coronary heart disease.” - Am J Med. 2002 Mar;112(4):298-304. - Note - here, the fact that there is no difference b/w dietary and non-dietary interventions is especially suspicious since dietery interventions are historically prone to low yield results (See latest JAMA diet studies, where weight loss is marginal and temporary even for those who choose to adhere to the diet)