Fish oil is composed mostly of long-chain omega-3 fatty acids known as EPA and DHA. A great source of omega-3s is oily coldwater fish, such as salmon, mackerel, tuna and sardines. Unfortunately, some of these, especially wild salmon, are becoming less plentiful and may be contaminated with environmental pollutants. Purified fish oil capsules might be a better source. EPA from fish oil is anti-inflammatory, which could be helpful in preventing cardiovascular disease, according to “Cardiology in Review.” DHA is part of healthy brain tissue, and according to a 2011 study published in the “Journal of Clinical Psychiatry,” might even help alleviate mental depression.