Fish oils come from fatty fish, also known as oily fish; specifically the tissue of fish such as trout, mackerel, tuna, herring, sardines, and salmon.
The fillets of oily fish contain up to 30 percent oil, but this figure varies. White fish, on the other hand, only contain high concentrations of oil in the liver, and have much less oil overall.
Apart from omega-3 fatty acids, oily fish are a good sources of vitamins A and D. Whitefish also contain these nutrients, but at much lower concentrations.
Health experts commonly tell people that oily fish have more health benefits than white fish. However, their recommendations have never been compellingly proven in large clinical trials.
Many health authorities around the world advise people to consume either plenty of oily fish or to take supplements, because of the supposed health benefits. Studies over the last 10 years have produced mixed results regarding the benefits of the dietary intake of fish oils.
Some people confuse fish oils and cod liver oil - they are different. Fish oils are extracted from the tissue of deep sea oily fish such as tuna, mackerel, herring, and salmon. Cod liver oil, by contrast, is extracted solely from the livers of cod.
Fish oils contain higher amounts of omega-3 fatty acids than cod liver oil, but lower amounts of vitamins A and D.
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Fast facts on fish oils
Here are some key points about fish oils. More detail and supporting information is in the main article.
What are omega-3 fatty acids?
Omega-3 fatty acids are types of fat commonly found in plant and marine life. There are two types that are plentiful in fatty fish:
Eicosapentaenoic acid (EPA) an omega-3 fatty acid that is found in fatty fish. When people refer to omega-3 fatty acids in fish, they are usually referring to EPA.
EPA is a precursor to chemicals involved in blood clotting and inflammation (prostaglandin-3, thromboxane-2, and leukotriene-5). Fish do not produce EPA, they obtain it from the algae that they eat.
DHA (docosahexaenoic acid) is an omega-3 fatty acid that is a major component of the human retina (in the eye), sperm, and cerebral cortex (in the brain).
Forty percent of all the polyunsaturated fatty acids (PUFAs) in the brain consist of DHA. DHA also makes up 60 percent of the PUFAs in the retina and half of the neuron's plasma membrane weight. Additionally, breast milk is rich in DHA.
Possible health benefits of fish oils
Research into the health benefits of fish oils has been contradictory.
Over the last 10 years, there have been dozens of studies on fish oils and omega-3 oils. Some have backed up health claims, while others have not.
1) Multiple sclerosis (MS)
Fish oils are said to help people with MS. However, a study carried out by researchers from University Hospital in Bergen, Norway, found that omega-3 fatty acids do not help people with MS.
2) Prostate cancer
One study found that fish oils may reduce the risk of developing prostate cancer if a low-fat diet is also followed; however, another linked omega-3 levels to a higher risk of aggressive prostate cancer.
A study published in the Journal of the National Cancer Institute found that high fish oil intake raises the risk of high-grade prostate cancer by 71 percent and all prostate cancers by 43 percent.
3) Post-natal (post-partum) depression
Fish oils consumed during pregnancy may help protect mothers from post-partum depression. According to Dr. Michelle Price Judge of the University of Connecticut School of Nursing: "DHA consumption during pregnancy at levels that are reasonably attained from foods has the potential to decrease symptoms of postpartum depression."
4) Mental health benefits
A pilot study carried out in 2007 suggested that fish oils may help young people with behavioral problems, especially those with attention deficit hyperactivity disorder (ADHD).
The 8-week study demonstrated that children who consumed 8-16 grams of EPA and DHA per day, showed significant improvements in their behavior (rated by both their parents and the psychiatrist working with them).
5) Memory benefits
Omega-3 fatty acid intake can help improve working memory in healthy young adults, researchers reported in the journal PLOS One.
However, the benefits of fish oils for cognitive function in older populations may be less impressive. A study by researchers at the University of Iowa suggested that high levels of omega-3 are of no benefit to cognitive decline in older women.
6) Heart benefits
Omega-3 fatty acids found in fish oils may protect the heart from mental stress.
A study study published in the American Journal of Physiology revealed that people who took fish oil supplements for longer than 1 month had improved cardiovascular function during mentally stressful tests.
7) Protection from Alzheimer's disease
Claims were made for many years that regular fish oil consumption would help prevent people from developing Alzheimer's disease. However, a major study in 2010 found that fish oils were no better than placebo at preventing Alzheimer's.
In contrast, a study published in Neurology in 2007 reported that a diet high in fish, omega-3 oils, fruit, and vegetables reduced dementia and Alzheimer's risk.
8) Protection from vision loss
Adequate dietary consumption of DHA protects people from age-related vision loss, Canadian researchers reported in the journal Investigative Ophthalmology & Visual Science.
A 2014 study published in the Journal of Neurology, Neurosurgery & Psychiatry claims epilepsy patients could reduce seizure frequency by consuming low doses of omega-3 fish oil every day.
The research team at the University of California-Los Angeles (UCLA) School of Medicine, says their findings may be particularly useful to epilepsy patients who no longer respond to medication.
10) Schizophrenia and psychotic disorders
In what was believed to be the first study of its kind, researchers revealed the omega-3 fatty acids found in fish oil may be effective for reducing the risk of psychosis.
The study, published in Nature Communications, details how a 12-week intervention with omega-3 supplements substantially reduced the long-term risk of developing psychotic disorders.
11) Benefits for the fetus
Omega-3 consumption may help boost fetal cognitive and motor development.
In a study published in 2008, scientists found that omega-3 consumption by the mother during the last 3 months of pregnancy improved the baby's sensory, cognitive, and motor development.
Do fish oil supplements offer heart benefits?
Does omega-3 benefit heart health?
Many people believe that a high consumption of omega-3 oils can benefit the heart. However, studies have produced mixed results.
Heart benefits found - a 2011 study, carried out by researchers at Michigan Technological University, found that fish oil consumption can improve blood flow by reducing triglyceride levels, as well as slowing down the growth rate of atherosclerotic plaques.
No heart benefits found - on the other hand, a review of 20 studies involving almost 70,000 people, found no compelling evidence linking fish oil supplements to a lower risk of heart attack, stroke, or early death.
Fish oils help patients with stents in their arteries - people with stents in their heart who took two blood-thinning drugs as well as omega-3 fatty acids were found to have a lower risk of heart attack compared with those not on fish oils.
Are low Japanese heart disease rates linked to high fish oil consumption?
Researchers from the University of Pittsburgh Graduate School of Public Health set out to determine why the incidence of heart disease in Japan is much lower than in America, Canada, Western Europe, and Australasia.
They reported that omega-3-rich fish consumption in Japan is much higher than in other developed nations. The authors believe that this is a main contributor to its relatively low rate of heart disease.
The scientists explained that the difference cannot be explained by genetic factors. Third and fourth generation Japanese-Americans have either the same or higher rates of hardening of the arteries (atherosclerosis) than the rest of the American population.
Study lead author Dr. Akira Sekikawa said:
"Our study suggests that very high levels of omega-3 fatty acids have strong properties that may help prevent the buildup of cholesterol in the arteries. Increasing fish intake to two times a week for healthy people is currently recommended in the United States.
Our study shows much higher intake of fish observed in the Japanese may have strong anti-atherogenic effect."
Japanese adult males consume approximately 3.75 ounces (100 grams) of fish each day. Their U.S. counterparts eat fish no more than twice a week.
North American diet deficient in omega-3 oils
Americans and Canadians eat too much meat and not enough fish, researchers from the University of British Columbia reported in the American Journal of Clinical Nutrition in 2008.
The authors added that the North American lifestyle means people are not getting adequate amounts of dietary omega-3 fatty acids. They emphasized that pregnant and breast-feeding women particularly need to ensure that they consume plenty of omega-3 oils.
They found that North American babies did not do as well on eye tests if they were deficient in omega-3 fatty acids while their mothers were pregnant.
Which foods are rich in omega-3 fatty acids?
The following foods are rich in omega-3 fatty acids:
- Oily fish - anchovies, herring, sardines, salmon, trout, and mackerel
- Perilla oil
- Eggs (especially ones that have "high in omega-3" written on the shell)
- Chia seeds
- Radish seeds, sprouted raw
- Fresh basil
- Leafy dark green vegetables, such as spinach
- Dried tarragon
How can vegans make sure their omega-3 fatty acid intake is sufficient?
Without proper planning, vegans and vegetarians have a much higher risk of being omega-3 deficient than humans who eat animal-sourced proteins.
The risk of not consuming enough omega-3 fatty acids is higher for vegans than vegetarians. Vegans may obtain their necessary omega-3 supplies by either taking supplements or adding plant-sourced omega-3 foods to their diet.
Several foods have omega oils added to them, such as margarines and spreads.
Flaxseed and rapeseed oils are very high in omega-3 fatty acids, while soybean and walnut oils are high in omega-6 fatty acids. Individuals should remember not to cook these delicate high omega-3 oils at a high temperature.