If you’ve gone fishing for information about any number of health conditions, you’ve likely dredged up something about fish oil.

While it has been touted as a wonder nutrient, you might wonder whether there’s a difference between fish, cod liver and krill oils.

Taking the mystery out of fish oil

Integrative naturopath Marta Browne said “fish oil” was a catch-all term for any oil made from fish, regardless of the type or part of the fish used. Herring, tuna, sardines, mackerel and anchovy are common sources.

Cod liver oil comes from the livers of cod. Krill oil comes from krill, a shrimp-like crustacean that is rich in omega-3 fatty acids.

While fish oil is high in omega-3s, it contains little vitamin A and D. Cod liver oil has fewer omega-3s, but is rich in vitamins A and D.

Accredited practising dietitian Sally Marchini said krill oil was most similar to fish oil. In fact, one study showed that taking krill oil and fish oil led to a similar increase in blood levels of omega-3 fatty acids, even though krill oil has only about two-thirds of the levels that fish oil does.

Which oil is best?

This depends on whether you’re looking to increase fatty acid or vitamin intake, Ms Browne said.

People looking primarily for a vitamin A and D supplement – such as indoor, office, or shift workers – would benefit more from a classic cod liver oil supplement.

People with eczema or acne in need of fatty acids, known as EPA/DHA, would benefit from a cold-processed fish oil or krill oil.

Do your research: The various oil supplements have many claimed benefits, but they don’t all necessarily stack up. Photo: Getty

Known benefits of fish oils

Numerous clinical trials have looked at supplementation with fish oils for inflammatory and autoimmune diseases such as rheumatoid arthritis, psoriasis, lupus, multiple sclerosis and migraines. Many of these showed significant benefit, including reduced disease activity and less use of anti-inflammatory drugs.

Fish oils have also been credited with helping to treat mood disorders and diabetes, and prevent some cancers. The Cancer Council, however, advises that is not yet enough evidence to draw any definite conclusions.

Omega-3s are also essential for heart health – just be sure to eat fresh fish, rather than supplements. A recent Cochrane review found that fish oil supplements had no effect on the risk of heart attack, stroke or death from cardiovascular disease.

Wherever possible, real food is always best, Ms Marchini said. She recommends three to four serves of deep sea fish a week (preferably of smaller varieties, which contain less mercury).

Ms Browne agreed, saying supplements should be used only to “fill in the gaps”.

When choosing supplements, be wary of dose and quality, as these can vary.

Ms Browne also noted that higher therapeutic doses (about 3000 milligrams a day) might have side effects. A qualified health professional can help with assessing your diet and, if necessary, recommending a quality supplement.

Keeping fish oil fresh

Fish oils can become rancid if they are not stored properly. To prevent the oil from decomposing:

• Store in a cool, dark place
• Check the use by date regularly
• Taste and smell the oil, or chew the gel cap slightly. If it smells like rotting fish, it’s time to throw away the capsules.