How Fish Oil Works

How Fish Oil Works

Fish oil is a substance derived from fatty fish. It is found in fish tissues and their belly cavity, and fillets may contain up to 30% fish oil.

Examples of fatty fish include sardines, anchovies, herring, salmon, tuna, halibut, trout, and mackerel.

Large predatory fish like sharks and swordfish also provide a large source of fish oil, but because of their position in the food chain, they accumulate toxic substances like mercury which come from the microalgae and smaller fish they eat. They are, therefore, not recommended as a source of fish oil.

How Fish Oil Works

Oily fish are a good source of the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These fatty acids are precursors of important substances in the body called eicosanoids that are known to reduce inflammation, a process that is associated with many diseases. They are also known to inhibit blood clotting, making fish oil useful for certain heart conditions.

Omega-3 fats are known as polyunsaturated fatty acids, and they play an important role in normal growth and development. They are also known as “brain food” because they are vital for brain function.

These critical fats have become popular because of their potential to reduce the risk of heart disease.

Thouh they are essential for health omega-3 fatty acids, like EPA and DHA, are important for health are not synthesized by the body. They have to come from foods in the diet such as fatty fish. The American Heart Association (AHA) therefore recommends eating 3.5 ounces cooked, oily fish at least 2 times a week. 1

Eating one serving (3.5 ounces) of oily fish provides about 1 gram of omega-3 fatty acids, although this may vary according to the type of fish. Salmon provides about 1.1-1.9 grams of fatty acids per 3-ounce serving while canned tuna only yields 0.17 – 0.24 grams.

Why People Take Fish Oil

Many people eat fish and take fish oil supplements for the various benefits they offer. Doctors and health providers may also advise patients to take them because research has shown that fish oil may be effective for:2

  • Lowering triglyceride levels by 20% to 50%
  • Preventing heart disease in healthy people
  • Reducing the risk for heart attacks and death in people with heart disease
  • Reducing high blood pressure
  • Reducing the risk for stroke
  • Improving symptoms of neurologic or psychiatric disorders like bipolar disorder, psychosis, and ADHD
  • Reducing the risk for cancer
  • Lowering cholesterol levels
  • Reducing the risk for age-related eye disease
  • Reducing the risk for recurrent miscarriages
  • Slowing down the progression of kidney disease

Many research studies are still investigating the possible benefits of fish oil for other conditions including:

  • Alzheimer’s disease and other neurologic conditions
  • Allergies and other skin conditions
  • Crohn’s disease and ulcerative colitis


Omega-3 fatty acids are essential fatty acids that are not manufactured by the body and therefore must be taken from the diet and from supplements. These fatty acids may be derived from a variety of food sources including fatty fish and other seafood, nuts and seeds, and certain vegetables. Oily fish are probably the best sources of these essential fatty acids.

Different people may need varying amounts of fish oil to derive the benefits it offers. Although the AHA recommends eating at least 3.5 ounces of fish (which contains approximately 1 gram of omega-3 fatty acid) twice a week for healthy people, people with special needs may have to take more in the form of supplements to obtain its therapeutic effects. In these cases dosing for fish oil supplements is based on the amount of EPA and DHA and not on the total amount of fish oil.3

The US Food and Drug Administration states that consuming up to 3000 mg of DHA/EPA per day from all sources (diet and supplements) is generally considered safe for most adults.4 Higher doses should be taken only with medical supervision. This is especially true for people who take fish oil for therapeutic purposes, such as a part of treatment for high triglyceride levels.


  1. Fish 101. AHA.
  2. Fish Oil. Medline Plus.
  3. Omega-3 Fatty Acids. UMMC.
  4. Can you overdose on DHA and EPA? DHA/EPA Omega-3 Institute.