For decades, dietary fat was demonized. All the western world’s health problems were caused by too much fat in our diets, doctors and researchers explained.
Based on recommendations from top medical institutions like the Mayo Clinic and Harvard School of Public Health, low-fat diets became incredibly popular in the 1980s and 1990s. Supermarket shelves were lined with non-fat cookies and fat-free ice cream, and people literally ate it up, assuming anything rid of dietary fat was “healthy.” But new research has totally flipped this old idea on its head—science now says that fats, even saturated fats, are not as bad as we once believed.
Yet even in the era when full-fat milk or cheese were deemed strictly off-limits, there was always a special carve-out for one particular type of fat. Omega-3 fatty acids made a name for themselves as “the good fat”—the only one that was okay to eat.
Fish oil supplements, one of the easiest ways to get your daily dose of omega-3s, are now a staple of every vitamin aisle. And whether you’re taking them or not (spoiler: you should be!), it’s helpful to know why, exactly, fish oil supplements is so good for your health. Read on for the full rundown.
What is fish oil?
It’s all in the name—fish oil comes from the fat found in fish. The fish don’t actually make the fats, but rather accumulate it by eating algae, krill, or other plants that produce omega-3 fatty acids. Fatty acids are classified by how many carbon atoms are in the chain. Fish oil itself is very high in two forms of long-chain omega-3 fatty acids: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). A third type, a short-chain omega-3 fatty acid called alpha-linolenic acid (ALA), is predominantly found in plant oils, but not fish. Researchers believe that most of the health benefits seen from omega-3 fats come from the two long-chain derivatives.
Omega-3 fatty acids are a necessary part of human metabolism, especially in young children. Our bodies can’t make omega-3 fatty acids—they can only be obtained through diet. Humans can convert ALA into EPA or DHA, but the process is very inefficient. For practical purposes, large quantities of EPA and DHA can only be obtained from fish or fish oil.
How do omega-3s benefit health?
Scientists and doctors are still trying to figure out exactly how omega-3 fatty acids produce the health benefits they do. The most common explanation is that omega-3 fatty acids by themselves aren’t responsible for health benefits, but that increased omega-3 consumption helps balance the ratio of omega-6 fatty acids in the body.
Omega-6 fatty acids are another class of dietary fats commonly found in meat and various plants. Both omega-3 and omega-6 fatty acids are converted into hormones called eicosanoids that regulate the body’s inflammatory responses and immune response.
Omega-6s produce more inflammatory eicosanoids than omega-3 fatty acids. And it seems that the appearance of omega-3s messes with the body’s ability to metabolize, or break down and use, omega-6s—in turn reducing the production of eicosanoids that cause inflammation. Basically, omega-3s get in the way of breaking down omega-6s, which leads to less inflammation overall. Omega-3s are also converted into eicosanoids at a slower rate than omega-6s. Because the omega-3 and omega-6 fatty acids compete to be transformed by a limited supply of enzymes into eicosanoids, decreasing the omega-6 fatty acid to omega-3 fatty acid ratio in the body would necessarily produce more of the eicosanoids derived from omega-3 fatty acids and decrease the total number of eicosanoids in the body overall.
The ratio of omega-6 to omega-3 fatty acids in western diets has shifted from a ratio of 2:1 to 20:1 by some estimates. Thus, increasing the intake of omega-3 fatty acids, particularly in the form of fish oil, can help restore the ratio of omega-6 to omega-3 fatty acids to healthier levels.
The many benefits of fish oil
When proper balance of omega-6s to omega-3s is achieved, both your body and mind both reap a number of benefits.
How fish oil benefits the heart
Supplementing with fish oil and increasing intake of omega-3 fatty acids is incredibly beneficial for heart health, affecting everything from triglyceride levels to blood pressure.
Lowers triglyceride levels
High blood pressure and increased levels of LDL cholesterol in blood is bad for cardiovascular health. There’s another type of lipid in the blood that you also need to worry about—triglycerides. Triglycerides are fats that are used to store the body’s excess energy, and they float around in your blood just like cholesterol.
Doctors aren’t sure exactly how triglycerides contribute to disease, but studies have shown a strong correlation between high blood triglyceride levels and arteriosclerosis, heart disease, stroke, high cholesterol, diabetes, and obesity.
When you get your cholesterol measured by your doctor, typically they’ll check your triglyceride and lipoprotein levels, too. Normally, blood triglyceride levels should be less than 150 milligrams per deciliter. If triglyceride levels exceed that upper limit, some cardiologists recommend fish oil in conjunction with diet and lifestyle changes.
There is strong scientific consensus that one of the primary health benefits of fish oil is its efficacy in lowering triglyceride levels. A study published in the journal “Arteriosclerosis” found that supplementing with low doses of EPA lowered triglyceride levels in men of all ages. A similar study published in the Journal of Nutritional Biochemistry found that fish oil supplementation lowered blood triglyceride levels in postmenopausal women.
One meta-analysis found that different doses of omega-3 fatty acids reduced triglycerides concentrations, especially in those with very high triglyceride levels at the outset. This research suggest the nutrient may be helpful in managing hypertriglyceridemia, or highly elevated triglyceride levels—a condition common in patients with HIV.
Another meta-analysis showed that DHA extracted from algae, rather than from fish, was also effective at reducing triglyceride levels.
Reduces blood pressure
High blood pressure, or hypertension, is bad for cardiovascular health and can cause damage to artery walls. Damaged artery walls can build up plaque faster than healthy walls, and as plaque builds up, the heart has to pump faster to pass the same volume of blood through a narrower passage.
Fish oil has been shown to reduce blood pressure and treat hypertension. In a 2013 meta-analysis of 17 studies following more than 1,500 participants, scientists found that fish oil supplementation resulted in a statistically significant reduction in blood pressure.
It’s not just extracted fish oil that can be used to treat blood pressure. According to a study published in Nutrition, eating salmon three times a week significantly reduced blood pressure in obese men. What’s particularly interesting about this study is that participants with lower levels of DHA at the start of the experiment exhibited the greatest reductions in blood pressure, implying that DHA consumption may directly affect blood pressure.
Prevents platelet aggregation
Platelets are blood cell fragments that float around in the bloodstream. Their normal function is to clump together at injury sites, forming blood clots to stop you from bleeding. However, platelets can also clump together at cholesterol plaques on the artery walls as well.
This platelet buildup can eventually block the flow of blood the heart, triggering a heart attack. Alternatively, the platelet clump can also break off and make its way to the brain, causing a blood clot or stroke.
There are several drugs that prevent the aggregation of platelets. The most popular are aspirin and statins, but research suggests fish oil might improve the efficacy of those two traditional treatments. A 2011 study published in Cardiology found that patients who took fish oil in addition to aspirin and statins exhibited a reduction in platelet aggregation compared to those who took only aspirin and statins. The study authors hypothesized that fish oil provides unique antiplatelet benefits different from the mechanism of action of aspirin and statins.
Likewise, a 2012 study found that fish oil reduced platelet aggregation in diabetes patients.
Reduces arterial stiffness
Hardening of the arteries, otherwise known as arteriosclerosis, reduces blood flow to the body’s organs and can force the heart to work harder. A number of factors contribute to arteriosclerosis, and rigid arteries can’t respond as well to changes in blood pressure caused by everything from stress to walking up the stairs. Fish oil has been shown to effectively reduce arterial stiffness, keeping pathways supple and healthy.
Another meta-analysis of 10 trials showed that fish oil supplementation significantly decreased arterial stiffness. Fish oil proved to be effective at decreasing arterial stiffness even when patients didn’t change factors like blood pressure, heart rate, or body mass index. The authors of the study concluded that the reduction in arterial stiffness, whatever the mechanism, may be at least partially responsible for the cardioprotective effects of fish oil.
Why fish oil is good for the brain
Omega-3 fatty acids, which are found in high concentrations in the brain, are crucial to healthy brain function. Research has shown that infants who don’t ingest enough omega-3s may develop vision and nerve problems. Naturally, scientists have looked at whether omega-3 fatty acids are effective at treating symptoms of mental health disorders and the evidence, while not conclusive, is promising.
Certain types may reduce symptoms of depression
In 2012, another meta-analysis found that while fish oil was not effective in treating the manic phase of bipolar disorder, it was effective at reducing the symptoms of the depressive phase—and was therefore recommended as an adjunctive treatment for the latter.
It could help reduce anxiety
Aside from depression, there’s some evidence that fish oil may have potential as an anti-anxiety treatment. In one 2011 study, healthy medical students who were given fish oil supplements showed a 20 percent reduction in anxiety symptoms versus those who were given placebos.
It’s a potential adjunct therapy for treating ADHD
Given that omega-3 fatty acids are an integral part of brain function, especially in childhood development, it is no surprise that fish oil may help kids with attention deficit hyperactivity disorder, or ADHD.
In a 2011 meta-analysis involving 699 children over 10 trials, those treated with fish oil exhibited small, but significant, improvements in ADHD symptoms. Also, a higher EPA content correlated with better efficacy—suggesting that type of fish oil can work alongside traditional drugs to treat ADHD. How does it work? The authors hypothesized that because fish oil has anti-inflammatory properties, it can alter cell membrane fluidity in the central nervous system. This, in turn, can positively impact the activity of two important neurotransmitters, serotonin and dopamine.
Where can I get fish oil?
You can easily get the benefits of fish oil without eating fish—just grab a supplement. Krill oil has the same type of omega-3 fatty acids, EPA and DHA, as fish oil. If you’d rather skip the pill and go for the real thing, make sure you choose a breed that’s high in both EPA and DHA. The following fish have the highest EPA and DHA content per serving:
Keep in mind, though, that certain fish such as mackerel, tuna, and swordfish have high levels of mercury, and should not consume more than 12.5 ounces a week. See a list of the mercury levels in common types of fish here.
Illustration by Katherine Prendergast
Photo credit: Paul Delmont