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If you eat fish, should you take a fish oil supplement? A dietitian explains

A registered dietitian recommends food first —and then a supplement, if needed.
The omega-­3s found in fish oil have been shown to be protective against the occurrence of many common diseases and conditions.
The omega-­3s found in fish oil have been shown to be protective against the occurrence of many common diseases and conditions. Yulia Reznikov / Getty Images

Chances are you or someone you know is taking a fish oil supplement. Fish oil is more of a veteran supplement versus the new kid on the block — and it’s also one of the most widely purchased supplements on the market. But, that doesn’t mean you know why it’s popular or why it keeps popping up in casual conversations. Here’s a primer for you.

The two main nutrients in fish oil are, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), commonly known as omega­-3 fatty acids. Omega-3 fatty acids are a type of polyunsaturated fats (aka PUFAs) and are considered “essential” fatty acids, because our bodies can’t make them on their own and we must get them from our diet or supplements. Another omega-3 you may be familiar with is alpha linolenic acid (ALA) which is found in plant sources such as flaxseed, chia seed, and walnuts. Our bodies can convert ALA into EPA and DHA but only in small amounts, unfortunately. In other words, we’re not too efficient at this process so, consuming EPA and DHA directly from foods and/or taking supplements is the best way to get these important nutrients in.

Why are EPA and DHA important?

Aside from playing important roles, DHA for vision and the nervous system and EPA for reducing inflammation, omega-­3s have been shown to be protective against the occurrence of many common diseases and conditions. A lot of research has been done on omega-3s, especially in the areas of cardiovascular disease, neurodevelopment and neuronal degeneration, cancer prevention, as well as on skin conditions and rheumatoid arthritis among others.

Cardiovascular disease:​ Omega­-3s have been shown to help keep cholesterol levels down and decrease triglyceride levels. Several systematic reviews and meta-analyses show that higher consumption of fish and higher dietary or blood levels of omega-3s are associated with a lower risk of heart failure, coronary disease, and fatal coronary heart disease. There’s a reason that fish is recommended as part of a healthy diet. It’s important to note that the evidence for the protective effect for omega-3 supplementation is stronger for people with existing coronary heart disease than for healthy individuals.

Hypertension: ​Omega-­3s have been shown to dilate blood vessels and suppress inflammation and multiple studies have shown a reduction in blood pressure due to omega-3 consumption.

Cancer:​ Omega­-3s may help control the growth of cancer cells. Researchers propose this is related to their anti-inflammatory effects. However, studies are inconsistent and vary from cancer to cancer. Although some evidence suggests that higher omega-3 intakes reduce the risk of breast and possibly colorectal cancers, additional research is still needed.

​Inflammatory diseases:​ Excessive stress, poor dietary habits, environmental toxicity, lack of sleep, and lack of exercise all contribute to low levels of chronic inflammation that often go undetected and can slowly build up for many years. This buildup is what will eventually lead to the development of chronic disease. Omega-3s have been shown to improve various inflammatory diseases (such as rheumatoid arthritis) since they’re converted to prostaglandins, natural anti-inflammatory agents.

​Mental health: ​Omega-3s have been shown to improve mental health disorders by keeping the brain and its signaling running smoothly. More research is needed here, but some studies (not all!) link omega-3s to a reduced risk of cognitive decline, Alzheimer’s disease, and dementia. People with Alzheimer’s disease have lower blood levels of DHA than cognitively healthy people.

What are some food sources of fish oil?

Well, this shouldn’t be a surprise — fish! Although amounts vary quite a bit, cold-water fish such as salmon, mackerel, tuna and herring are going to be your best omega-3 sources.

Should I take a supplement?

I always say food first, then supplement if needed. The American Heart Association (AHA) recommends eating at least two 3.5-ounce servings of fish per week and other government recommendations include replacing some meat with fish. Many people, even those who eat a healthy diet, still fall short with omega-3s and in this case supplementing is often recommended.

A typical fish oil supplement provides about 1,000 mg of fish oil. But, this doesn’t mean it’s all DHA and EPA. Brands will vary but many supplements that contain 1,000 mg will have about 120 mg DHA and 180 mg EPA. It’s also important to check supplement labels so that you’re aware of the types and amounts of omega-3s you’re buying and consuming.

Is it safe to take?

The AHA says taking up to 3 grams of fish oil daily in supplement form is considered safe. Always discuss it with your doctor first especially if you’re on any medications and/or have any underlying conditions. The recommended adequate intake is 1.6g/day for men and 1.1g/day for women. The FDA has concluded that dietary supplements providing no more than 5 g/day EPA and DHA are safe when used as recommended.

Are there any side effects?

Side effects from omega-3 fish oil may include a fishy taste (or breath!), upset stomach, and nausea.

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