I too have always assumed they were good. I came across a blog that I think is great. He is a proponent of Fish Oil as it acts as an anti-inflammatory. (His work is dense but digestible. If you're interested in health at all I suggest poking around a bit on there).
Well, like anything, I recently questioned whether fish oil was a miracle drug. I found an interesting article discussing fish oil in a warning light, comparing it to harmful hormone and x-ray usage in previous years. Here are some choice sections of the lengthy article. (Full article here).
"For a few decades, x-ray treatments were used to relieve inflammatory conditions, and most of the doctors who promoted the treatment were able to retire before their patients began suffering the fatal effects of atrophy, fibrosis, and cancer. (But a few people are still advocating x-ray therapy for inflammatory diseases, e.g., Hildebrandt, et al., 2003.) The fish oil fad is now just as old as the x-ray fad was at its peak of popularity, and if its anti inflammatory actions involve the same mechanisms as the anti inflammatory immunosuppressive x-ray treatments, then we can expect to see another epidemic of fibrotic conditions and cancer in about 15 to 20 years."Scary thought. I see this sort of thing in literature as a plot device -- yet here it is as medical information.
"In 2004, a study of 29,133 men reported that the use of omega-3 oil or consumption of fish didn't decrease depression or suicide, and in 2001, a study of 42,612 men and women reported that after more than 9 years the use of cod liver oil showed no protective effect against coronary heart disease (Hakkarainen, et al., 2004; Egeland, et al., 2001)."No results. There's a head-scratcher.
"When animals are fed fish oil and then exposed to bacteria, their immunosuppressed thymic (T) cells cause them to succumb to the infection more easily than animals fed coconut oil or a fat free diet. Natural killer cells, which eliminate cancer cells and virus infected cells, are decreased after eating fish oil, and T suppressor cells are often increased. More subtle interference with immunity is produced by the actions of PUFA on the "immune synapse," a contact between cells that permits the transmission of immunological information. The immunosuppressive effect of fish oil is recognized as a useful aid in preventing the rejection of transplanted organs, but some studies are showing that survival a year after transplantation isn't improved."Furthermore, in the article it was said that the test animals were very resistant to eating fishy foods. Do they know something we don't?
As with anything, proceed with caution. I personally am discontinuing fish-oil supplementation. The only real reason to take it is to improve your Omega-6 to Omega-3 ratio anyway, but those of us who eat low Omega-6's shouldn't even worry too much (more reason to eat on the Paleo Diet).
In my opinion, you should aim for a tight ratio without supplementation.
Here's a short article talking about both Omega-3's and 6's. Check it out.
This of this segment as Step 1 to fixing your ratio:
"... [to] cut down on omega-6 levels, [reduce] consumption of processed and fast foods and polyunsaturated vegetable oils (corn, sunflower, safflower, soy, and cottonseed, for example). At home, use extra virgin olive oil for cooking and in salad dressings."