Greatist’s #WTFis series looks at new trends in health and fitness to explain what the heck they are, why people care, and if they live up to the hype.

As far as supplements go, fish oil capsules have been marketed as the MVP of the bunch: They’re chock-full of polyunsaturated omega-3 fatty acids, which boast benefits like reducing the risk heart disease, lowering blood pressure, stopping cognitive decline, and even alleviating asthmaFish oil: what is the role in cardiovascular health? Brinson BE, Miller S. University of North Carolina Eshelman School of Pharmacy, Chapel Hill, NC, USA. The Journal of Pharmacy Practice. 2012 February; 25(1):69-74.Docosahexaenoic acid-concentrated fish oil supplementation in subjects with mild cognitive impairment (MCI): a 12-month randomized, double-blind, placebo-controlled trial. Lee LK, Shahar S, Chin AV, Yusoff NA. Nutrition Science Program, School of Health Care Sciences, Faculty of Health Sciences, Universiti Kebangsaan Malaysia, Kuala Lampur, Malaysia. Psychopharmacology. 2013 February; 225(3):605-12.Protective effect of fish oil supplementation on exercise-induced bronchoconstriction in asthma. Mickleborough TD, Lindley MR, Ionescu AA, Fly AD. Human Performance and Exercise Biochemistry Laboratory, Department of Kinesiology, Indiana University, Bloomington, IN, USA. Chest. 2006 January; 129(1):39-49.. Do the health claims behind fish oil hold water, or are they as slippery as the marine animals themselves?

Photo: jcoterhals

The Lowdown

The popular pills contain oil pressed from actual chunks of fish that have been steamed, separated, and purified. Appetizing, right? The fishy oil contains a concentrated dose of omega-3 fatty acids, plus some added vitamin E to prevent spoilage. Some pill manufacturers boost (possible) health benefits by adding other vitamins and minerals like calcium, iron, or vitamins A, B, C, or D into the mix. Most capsules contain 1,000 mg of fish oil, although the actual dosage of omega-3 fatty acids in each pill varies between brands, usually from 200 mg to 600 mg.

Omega-3 fatty acids (often just called omega-3s) are essential healthy fats the human body can’t produce but requires for functions as diverse as controlling blood clotting, forming cell membranes, absorbing vitamins, and keeping skin and hair healthy. There are two main categories of omega-3s: ALA (alpha-linolenic acid), which comes from vegetarian sources like flaxseed, nuts, and various vegetable, nut, and seed oils, and EPA and DHA (eicosapentaenoic acid and docosahexaenoic acid — try saying that five times fast), which we can get via fatty fish and algae. Salmon, herring, mackerel, and anchovies are particularly good sources of these EPA and DHA omega-3s. (A note to vegetarians: The body can convert some ALA fatty acids to EPA and DHA, so it’s possible to skip the flounder and still get the benefits.)

Although they’re often lumped together (and usually mixed up inside fish oil capsules or gummy vitamins), EPA and DHA do different jobs in the body. EPA works as an anti-inflammatory throughout the body, including the brain. DHA is essential in the maintenance and creation of fluid cell membranes. Both types of omega-3 fatty acid can reduce triglyceride levels and increase “good” HDL cholesterol in the body. Fish oil’s alleged benefits have made it a one-stop shop for a number of medical problems — regardless of whether or not the science behind it is legit. Because of its beneficial associations with lowering triglycerides and increasing good cholesterol, fish oil has a strong (although perhaps overexaggerated) link to heart health, and it’s often recommended to those at risk of heart attacks and strokes. EPA’s link to brain blood flow means it’s become a home remedy-type treatment for depression, ADHD, Alzheimer’s, and other brain disorders. Fish oil is also prescribed to keep eyes moist and treat glaucoma and age-related macular degeneration.

The Buzz — Why Do People Care Now?

There’s something a bit fishy about all the health claims surrounding these magical, health-boosting pills, and last year, scientists harpooned some of fish oil’s purported benefits. A team of Greek researchers analyzed 20 studies on fish oil that, when combined, looked at more than 68,000 patients. They found that, based on results from these 20 studies, fish oil supplements did not lower risk of stroke, death, or cardiovascular disease (including heart attack)Association between omega-3 fatty acid supplementation and risk of major cardiovascular disease events: a systematic review and meta-analysis. Rizos EC, Ntzani EE, Bika E, Kostapanos MS, Elisaf MS. Lipid Disorders Clinic, Department of Internal Medicine, University Hospital of Ioannina, Ioannina, Greece. JAMA: The Journal of the American Medical Association. 2012 September 12;308(10):1024-33.n-3 fatty acids in patients with multiple cardiovascular risk factors. Risk and Prevention Study Group, Roncaglioni MC, Tombesi M, Avanzini F, Barlera S, Caimi V, Longoni P, Marzona I, Milani V, Silletta MG, Tognoni G, Marchioli R. The New England Journal of Medicine, 2013 May 9. 368 (19): 1800-8.. Recent research has also debunked the idea that omega-3s can altogether prevent cognitive decline and dementia in older adultsOmega 3 fatty acid for the prevention of cognitive decline and dementia. Sydenham E, Dangour AD, Lim WS. Cochrane Injuries Group, London School of Hygiene and Tropical Medicine. London, UK. The Cochrane Database of Systematic Reviews, 2012 June 13;6.. Scientists from Yale were unwilling to totally reject the idea that fish oil can treat depression, but they concluded swallowing extra omega-3 fatty acids had a “small, non-significant benefit” for curing the bluesOmega-3 fatty acids for the treatment of depression: systematic review and meta-analysis. Bloch MH, Hannestad J. Department of Psychiatry, Yale University School of Medicine, New Haven, CT, USA. Molecular Psychiatry, 2012 December;17(12):1272-82..

It’s important to remember that omega-3s don’t exist in a vacuum. The body requires both omega-3s and their close cousins, omega-6 fatty acids, to function properly. These days, the average Westerner consumes between 10 and 25 times more omega-6s (usually in the form of vegetable oils) than omega-3s. Studies have shown that a ratio closer to 2:1 or even 1:1 is best for healthThe importance of the ratio of omega-6/omega-3 essential fatty acids. Simopoulos AP. The Center for Genetics, Nutrition, and Health, Washington, DC, USA. Biomedicine & Pharmacotherapy. 2002 October; 56 (8):365-79.. The imbalance of omega-6s and omega-3s can result in inflammation, which causes many of the disorders that fish oil can “cure.” In many cases, fish oil is recommended to correct the imbalanced ratio, stanching inflammation that’s caused by a dietary overload of omega-6s.

Getting too jazzed about the miracle pills can have negative effects, too: Overdosing on the supplement (according to Greatist Expert Eugene Babenko, that means popping over 20 grams of fish oil a day) can have side effects like nausea, nosebleeds, headaches, short-term memory loss, high blood sugar, and a weakened immune system. Recent studies have also linked high doses of omega-3s with increased prostate cancer risk, but the theory is so new and untested that it’s hard to say if fish oil is at all to blamePlasma phospholipid faty acids and prostate cancer risk in the SELECT trial. Brasky TM, Darke AK, Song X, Tangen CM, Goodman PJ, Thompson IM, Meyskens FL Jr, Goodman GE, Minasian LM, Parnes HL, Klein EA, Kristal AR. The Journal of the National Cancer Institute. 2013 July 10..

Fish oil isn’t just controversial in the medical arena — the capsules of fish juice raise the same environmental and health issues that a tasty fillet grilled salmon or dish of tuna tartare mightFish oils, coronary heart disease, and the environment. Greene J, Ashburn SM, Razzouk L, Smith DA. Mount Sinai Medical Center, New York, NY, USA. The American Journal of Public Health, 2013 February 14.. A significant percentage of all fish oil comes from a stinky member of the herring family called Atlantic menhaden. It’s loaded with omega-3 fatty acids, which is both a blessing and a curse. Menhaden is lower in harmful mercury, dioxins, and PCBs that contaminate many of its fishy friends like tuna or farmed salmon. But, perhaps thanks to the popularity of fish oil supplements, the fish is now a hot commodity and wild populations have plummeted in the menhaden’s favorite coastal hangouts.

The Verdict

Right now, researchers still don’t know exactly how fish oil affects healthy bodies. While some of fish oil’s claims have been debunked in the lab and by prominent docs, other studies are still proving that the stinky substance might, in fact, help keep us healthy in the long run.

The question of whether to take fish oil supplements remains a toughie.Greatist Expert Dr. John Mandrola explains that nearly all pro-fish oil research is a bit murky (dare we say, fishy?) because different studies routinely use varying strengths of omega-3s. These days, most docs (including the American Heart Association) recommend getting plenty of omega-3s by eating at least two servings of fish per week. Adding healthy oils and fats to the diet via other sources doesn’t hurt, either.

For a more specific “yes or no” answer, talk to your doctor, and study up on the subject beforehand. If the recent media uproar about fish oil has taught us anything, it’s that the supplement might make a difference for certain conditions, but it probably won’t cure everything that ails us.

Do you take fish oil supplements? Has new research surrounding fish oil affected your decision? Tell us about it in the comments below or tweet the author @SophBreene.