Salmon, sardines, mackerel, and herring regularly appear on lists of the healthiest foods you can eat. Much of their reputation comes down to two nutrients: the long-chain omega-3 fatty acids EPA and DHA.
There is plenty of research behind that enthusiasm. Diets containing fish have been associated with better cardiovascular health and a lower risk of cognitive decline. DHA is also an important structural component of the brain.
But there is a wrinkle that often gets lost when these findings reach social media.
A significant amount of experimental research on the benefits of omega-3s doesn’t actually ask people to eat more oily fish. Instead, researchers give participants concentrated EPA and DHA supplements and compare them with a placebo.
That’s useful for determining what particular fatty acids might do. But a capsule of isolated omega-3s isn’t the same thing as a serving of sardines.
And the distinction matters in both directions. A disappointing fish oil trial doesn’t prove that fish isn’t healthy, just as a study associating fish consumption with better health doesn’t prove that omega-3s alone deserve all the credit.
So what do we actually know about oily fish?
Why Oily Fish Gets So Much Attention
Fatty or oily fish differ from many leaner varieties because they store considerably more fat in their tissues. That makes species such as salmon, sardines, herring, and Atlantic mackerel particularly rich sources of EPA and DHA.
These fats play important biological roles. DHA is especially concentrated in the brain and retina, while EPA and DHA are involved in processes affecting cell membranes, inflammation, blood lipids, and cardiovascular function.
But fish isn’t simply an omega-3 delivery system.
It also provides high-quality protein and nutrients such as vitamin B12, selenium, iodine, and varying amounts of vitamin D. Sardines have another nutritional advantage: when canned with their soft edible bones, they can provide substantial calcium.
That’s one reason comparing fish directly with a fish-oil capsule can be misleading. One is a whole food containing numerous nutrients. The other is designed to deliver particular fatty acids.
The FDA makes a similar distinction in its guidance on fish and omega-3 supplements, noting that supplements don’t provide the protein, vitamins, minerals, and other nutrients found in fish.
What About the Brain?
The evidence surrounding fish and brain health is encouraging, although it needs to be interpreted carefully.
A 2024 meta-analysis of 35 observational studies examined fish consumption and cognitive outcomes. Compared with people reporting the lowest fish intake, those consuming the most had an 18% lower associated risk of cognitive impairment or decline. Higher fish consumption was also associated with lower rates of dementia and Alzheimer’s disease, although the researchers said more evidence was needed to strengthen those conclusions.
Those numbers sound impressive, but this wasn’t a clinical trial in which researchers randomly assigned hundreds of thousands of people to eat sardines or avoid them.
Most of the evidence was observational. People who regularly eat fish may differ in many other ways from people who rarely do. Researchers attempt to adjust for those differences, but they can’t eliminate every possible confounding factor.
So we can reasonably say that fish consumption is associated with better cognitive outcomes. Saying fish prevents dementia would go considerably further than the evidence allows.
Read More: 6 Dietary Habits That May Lower Your Dementia Risk Before Symptoms Start The Hearty Soul
Omega-3 Supplements Tell a Different Story
If omega-3s explain the association, it seems logical that putting EPA and DHA into capsules should produce similar benefits.
That hasn’t consistently happened.
A systematic review examining 24 omega-3 supplementation studies found improved cognition in only five. All four trials involving people with Alzheimer’s disease reported null results, while findings among cognitively healthy people and those with mild cognitive impairment were frequently negative or inconclusive.
Other research has reached somewhat more encouraging conclusions in certain populations or for particular cognitive measures, so it’s too simplistic to say omega-3 supplements “don’t work.”
A separate 2024 meta-analysis of 24 randomized trials involving 9,660 people without dementia, for example, found evidence of potential benefits for executive function, with results varying according to factors including dose and treatment duration.
The broader picture, however, is much less convincing than “take fish oil to prevent dementia.”
And importantly, these trials are studies of omega-3 supplementation, not studies of eating oily fish.
A Capsule Isn’t a Piece of Fish
Supplement trials typically isolate EPA and DHA in specific doses and formulations. That makes sense scientifically because researchers need to know exactly what participants are receiving.
Whole foods are considerably messier.
Someone eating sardines gets omega-3s alongside protein, minerals, vitamins, and other compounds. Eating fish might also mean they’re eating less of something else. Replacing processed meat with salmon, for example, is a different nutritional intervention from simply adding a fish-oil capsule to an otherwise unchanged diet.
Even the chemical form of omega-3s may matter.
Researchers are investigating whether different forms of DHA are transported into the brain differently, including whether DHA bound to lysophosphatidylcholine, or LPC-DHA, may offer advantages over other forms.
A clinical trial is now investigating this question by comparing LPC-DHA with another DHA formulation in older adults experiencing early signs of cognitive or memory decline. Researchers are examining whether the formulations differ in their effects on DHA levels in the blood and cerebrospinal fluid as well as several neurological biomarkers.
That’s an intriguing possibility, but the research is still developing. It shouldn’t yet be treated as the explanation for why fish consumption and supplement trials sometimes produce different results.
That Doesn’t Mean Fish Oil Is Useless
Fish oil’s reputation has arguably swung too far in both directions. It has been promoted as a near-universal wellness supplement, while critics sometimes dismiss it as useless.
The evidence is more complicated.
Omega-3 supplementation can lower triglycerides. A major Cochrane review of 86 randomized trials involving more than 162,000 participants found that increasing EPA and DHA reduced triglycerides by about 15%. It found little or no effect on overall deaths or cardiovascular events, but there was evidence of a small reduction in coronary events and coronary heart disease deaths. Most of the EPA and DHA trials involved supplements rather than oily fish.
That also highlights another problem with treating “fish oil” as one intervention. A high-dose prescription preparation of purified EPA isn’t necessarily equivalent to an over-the-counter capsule containing a mixture of EPA and DHA.
Higher doses aren’t automatically better either. The NIH Office of Dietary Supplements notes that two large clinical trials using 4 grams of omega-3s per day for several years found a slightly increased risk of atrial fibrillation among people with cardiovascular disease or at high cardiovascular risk. Omega-3 supplements can also interact with some medications.
People considering high-dose omega-3 supplements for a medical purpose should therefore discuss them with their healthcare provider.
Read More: Up to 20M Healthy Americans Who Take Common Supplement May Be at Raised Risk of Stroke and Atrial Fibrillation, Study Finds The Hearty Soul
What About Mercury?
Fish also comes with a consideration that varies considerably by species: environmental contaminants.
Methylmercury is the best-known concern. Nearly all fish contain at least traces of it, but concentrations vary dramatically. Mercury accumulates through the food chain, meaning larger, longer-lived predatory fish generally contain more.
That’s actually one advantage of several popular oily fish. FDA data place sardines, salmon, and Atlantic mackerel among lower-mercury “Best Choices.” Swordfish, shark, king mackerel, and bigeye tuna are among the species authorities recommend avoiding during pregnancy because of their higher mercury concentrations.
Pregnancy therefore isn’t a reason to automatically eliminate fish.
In fact, FDA and EPA guidance recommends that people who are pregnant or breastfeeding eat 8 to 12 ounces of lower-mercury fish per week. Fish supplies protein, fatty acids, vitamins, and minerals important during development, while choosing appropriate species helps limit mercury exposure.
The goal is to choose fish wisely, not simply avoid it.
So, Is Oily Fish Really Good for You?
Overall, the evidence points toward yes, with some important qualifications.
Oily fish provides EPA and DHA alongside protein and numerous micronutrients, and fish consumption is consistently associated with favorable health outcomes. The American Heart Association recommends eating two servings of fish, particularly fatty fish, each week, while the FDA says strong evidence supports eating fish as part of a healthy dietary pattern for heart health.
What we shouldn’t do is blur together every type of evidence.
A trial showing a benefit from concentrated EPA or DHA doesn’t automatically prove that eating mackerel produces the same effect. A negative fish-oil trial doesn’t demonstrate that salmon is useless. And an observational study linking fish consumption with lower dementia risk doesn’t prove that omega-3s prevent Alzheimer’s.
Nutrition rarely comes down to one molecule.
For people who enjoy fish, salmon, sardines, herring, and lower-mercury varieties of mackerel remain nutrient-dense choices with a strong place in a healthy diet. Sardines in particular combine omega-3s with protein and, when their bones are eaten, calcium.
Fish oil supplements may have benefits of their own, particularly for specific people and specific health goals. But swallowing EPA and DHA in a capsule and eating a serving of oily fish are not nutritionally interchangeable.
Oily fish doesn’t need to be a miracle food to be good for you. The evidence is compelling enough without pretending that every omega-3 study is really a study about fish.
Disclaimer: This information is not intended to be a substitute for professional medical advice, diagnosis or treatment and is for information only. Always seek the advice of your physician or another qualified health provider with any questions about your medical condition and/or current medication. Do not disregard professional medical advice or delay seeking advice or treatment because of something you have read here.
A.I. Disclaimer: This article was created with AI assistance and edited by a human for accuracy and clarity.