December 15, 2017
Salmon slices seasoned with lemon, sesame oil and parsley

Catch the Health Benefits of Fish

by Berkeley Wellness  |  

Compared to people who don’t eat fish, those who do tend to live longer and enjoy lower risks of cardiovascular disease, and may even boost their brain health. Fish is the best source of two omega-3 polyunsaturated fats—eicosapentenoic acid (EPA) and docosahexenoic acid (DHA)—linked to health benefits. Fish also contains vitamins, minerals, and other fats that may work with the omega-3s to protect the heart and overall health.

Rich in protein and low in saturated fat, fish can also replace less-healthful foods in your diet such as red meat. The benefits of fish generally outweigh potential risks from contaminants (such as mercury and PCBs; see Cautions About Fish Consumption) that may be present, especially if you eat mostly smaller fish (lower on the food chain) and vary your intake.

Here are answers to key questions about fish and your health.

How does eating fish help to protect your heart?

Observational studies consistently show that people who eat more fish, especially fatty fish, are at reduced risk for heart attacks, stroke, and other coronary problems than those who eat less. Exactly how fish could reduce the risk is not clear, and such studies have built-in limits (see inset below). Research, some done in the lab, has found that omega-3 fats in fish oil help prevent arrhythmias and blood clots, reduce inflammation, make arteries more flexible, lower triglycerides (substantially, when taken in high doses), and reduce blood pressure (modestly). Other factors may also be involved.

A meta-analysis published in Mayo Clinic Proceedings in January 2017 looked at 16 observational studies on omega-3 fats and events associated with coronary artery disease, notably heart attacks. These studies looked mostly at fish consumption rather than fish oil pills. Overall, people consuming the most omega-3s had an 18 percent reduction in coronary risk.

Those findings align with a large study in the journal Circulation: Heart Failure, which included only women. Those who ate five or more servings a week of baked or broiled fish (but not fried) over a 10-year period had a 30 percent reduced risk of heart failure, compared to women who ate less than one serving a month. Fattier fish such as salmon, higher in omega-3 fats, were most protective.

Perhaps the strongest evidence for the cardiovascular benefits of eating fish—and how those might translate to longevity—came from a 2013 study in the Annals of Internal Medicine. The study involved 2,700 healthy Americans over 65 (most in their seventies), whose blood levels of marine omega-3 fats were measured. People taking omega-3 supplements were excluded, so the blood levels were a marker for fish intake. After 16 years, the researchers correlated these omega-3 levels with the number of deaths, adjusting for other dietary, lifestyle, and cardiovascular factors. This was the first large study of healthy people that used an objective measure of omega-3 intake (as opposed to self-reports of fish intake, which are much less reliable) to evaluate the effect on mortality rates.

People with the highest initial omega-3 blood levels were 27 percent less likely to die during the 16 years of the study than those with the lowest blood levels, with the greatest reduction seen in deaths from cardiovascular disease (notably those caused by abnormal heart rhythms). As a result, they lived 2.2 years longer, on average.

You don’t have to go overboard to get the benefits. The researchers estimated that the biggest increase in omega-3 blood levels would come from eating about two servings (3 to 4 ounces each) of fatty fish a week.

What are omega-3 fats?

The omega-3s found in fish get their name from their chemical structure: Like all organic molecules, these fats are made up of long chains of carbon atoms. In less-healthy saturated fats, all the possible bonds on these carbon atoms are occupied by hydrogen atoms (hence saturated). Monounsaturated fats, like those in olive oil, have one (mono) “open” carbon bond, while polyunsaturated fats such as omega-3s have several (poly). The first unsaturated spot in omega-3s occurs three from the end—therefore, “omega-3.”

Omega-3s in Fish: Top Picks

Here are the best seafood choices in terms of their heart-healthy omega-3 content.

How much omega-3s do you need?

You can eat no fish and get none of its omega-3 fats and still stay perfectly healthy, especially if your overall diet is good. The U.S. has no official recommended dietary intake (RDA) or Daily Value for the omega-3s fats in fish, EPA and DHA, because they are not “essential” nutrients—that is, the body can make them, in limited amounts, from an omega-3 fat found in plant foods, called alpha linolenic acid.

Other health authorities across the world have issued EPA/DHA recommendations—which vary widely, reflecting the uncertainty about how much is needed for optimal health and disease prevention. For instance, several countries in Europe recommend 250 milligrams of EPA/DHA a day, on average, for healthy adults. Australia and New Zealand recommend less (160 milligrams), France more (500 milligrams). Russia tops the list, at 1,300 milligrams daily.

In 2016, the Global Organization for EPA and DHA Omega-3s, a U.S.-based trade association, endorsed a daily recommendation of 500 milligrams. That’s in line with the recommendation of the Academy of Nutrition and Dietetics.

If you eat at least two servings of fatty fish a week—what the American Heart Association recommends for general heart health—it’s fairly easy to get an average of about 250 milligrams a day (more or less, depending on your selections and portion sizes). But Americans tend to favor less-fatty types such as canned light tuna, whitefish, and shrimp.

Are less-fatty varieties such as tilapia worth eating?

Even if you choose varieties relatively low in omega-3s, putting more fish on your plate can be good for you. For most people, consuming more fish and other seafood means eating relatively less of the pizzas, hamburgers, processed meats, and fried foods that make up so much of the typical Western diet. Those entrée choices tend to be much higher in saturated fat and sodium than meals centered on seafood (unless, of course, you slather on creamy sauces or dunk your seafood in butter).

Tilapia is a good example. This white-fleshed freshwater fish is mild in flavor, which makes it appealing to people who don’t like “fishy” fish. It’s the world’s second most farmed fish (after carp) and the fourth most consumed type of seafood in the U.S. (after shrimp, tuna, and salmon). But if you’re looking for a lot of heart-healthy omega-3 fats, tilapia is not the best choice: It has very little fat—2 to 3 grams per 3.5-ounce serving, of which less than 0.2 grams is omega-3s (in contrast, both wild and farmed salmon have more than 1.5 grams of omega-3s per serving). Farmed tilapia is particularly low in omega-3s because its diet is predominantly corn- and soymeal-based, in contrast to the omega-3-rich algae and other aquatic plants that wild tilapia feed on.

Tilapia has gotten a lot of bad press in recent years, in part because of those low omega-3 levels. But most experts agree that if you enjoy mild-flavored, affordable tilapia, it’s still a better choice than most main dishes. After all, tilapia is relatively low in calories (130 per serving, cooked), sodium (55 milligrams plus salt added in cooking), and saturated fat (1 gram, plus any added in cooking) and rich in protein (26 grams). Compare that to the 560 calories, 1,000 milligrams of sodium, and 8 grams of saturated fat in a typical fast-food burger, which has about the same amount of protein.

Does eating fish help to protect your brain?

The evidence that eating fish helps protect the brain is not as strong as for cardiovascular benefits. Many studies have found that what’s good for the heart is also good for the brain, whose functioning depends on a healthy blood flow. Moreover, DHA is a key structural component of the brain.

Most published observational studies have found a relationship between greater fish intake and reduced incidence of cognitive decline, including Alzheimer’s disease. Among the first was the Rotterdam Study, published in 1997 in Annals of Neurology: People (ages 55 and older, cognitively healthy initially) who ate the most fish (at least 5 ounces a week, on average) had a 50 percent lower risk of developing dementia (primarily Alzheimer’s disease) after two years of follow-up. The PAQUID Study in France, published in 2002 in BMJ, found that older adults who ate at least one fish meal weekly were 35 percent less likely to develop Alzheimer’s over seven years. And the CHAP Study, published in 2005 in Archives of Neurology, observed reduced decline in global cognition over six years among people over age 65 who ate fish at least weekly.

Another approach to investigating the fish-brain connection is to measure omega-3 concentrations in the blood. In research published in 2006 in Archives of Neurology, scientists looked at 899 participants in the long-running Framingham Heart Study, all over age 76 and initially free of dementia. Those with the highest DHA levels had only half the dementia risk of those with the lowest DHA after nine years.

Data from the Cardiovascular Health Study, published in Neurology in 2008 and with a follow-up in the Journal of the American Heart Association in 2013, linked omega-3s and fish intake with greater brain volume (brain shrinkage is associated with increased cognitive decline) and fewer brain abnormalities. Researchers used MRI scans to compare the brains of those who ate fish weekly with those of non-fish eaters. The beneficial associations were found for eating baked and broiled fish, but not fried fish.

Concerns about mercury—a known neurotoxin—were allayed by an unusual 2016 study in the Journal of the American Medical Association. Researchers looked at brain autopsies of 286 people (average age 90) and correlated the findings with the subjects’ seafood intake during the years before death. Among the 23 percent of subjects with a key genotype (ApoE4) associated with Alzheimer’s risk, those who had eaten seafood at least once a week showed fewer signs of dementia-related brain changes than those who ate little or none; no effect was seen in those without the genotype. Reassuringly, though mercury levels in the brains increased with seafood intake, this was not associated with dementia-related signs.

Results from clinical trials—the gold standard of scientific research—on fish and cognition have yielded mixed results. Most such trials have relied on supplements of fish oil rather than actual fish (see Alternatives to Eating Fish).

Casting Doubt on Observational Fish Studies

Most studies suggesting health benefits from eating fish have been observational. In contrast, nearly all clinical trials have used fish oil capsules, and most have had disappointing results.

What about rheumatoid arthritis?

A 2017 study published in Arthritis Care & Research found that people with rheumatoid arthritis who consumed more fish suffered less pain and swelling. Rheumatoid arthritis is an autoimmune disease that causes inflammation in joints and various organs. Researchers asked 176 participants about their consumption of non-fried fish, then compared those responses to a “disease activity score.” As fish intake went up, average scores for joint pain and swelling went down. The association held even when results were adjusted for other health and behavioral factors, as well as fish oil supplement use.

Can eating fish help to prevent diabetes?

Some researchers are hopeful about this, but studies thus far have not found consistent benefits. A 15-year study published in Diabetes Care in 2009, for example, failed to find any beneficial effect of total fish consumption, type of fish, or EPA and DHA intake on the risk of type 2 diabetes.

The American Diabetes Association recommends fish as a healthy choice for people who already have the disease. And eating fish may help protect against other health problems often associated with diabetes. An English study reported that fish consumption lowers abnormal levels of protein in the urine—a sign of kidney disease—in people with diabetes.

Another study, published in JAMA Ophthalmologyin 2016,suggested that if you have type 2 diabetes, eating fatty fish may reduce the risk of diabetic retinopathy, a complication of diabetes that often causes blindness. This was a new analysis of data from the Spanish PREDIMED trial of potential benefits of the Mediterranean diet and focused on 3,400 participants (average age 67) who had type 2 diabetes. Researchers correlated participants’ intake of omega-3 fats from seafood with their risk of diabetic retinopathy over a six-year period. Those consuming at least 500 milligrams of marine omega-3 fats a day, on average—equal to about two or three servings of fatty fish a week—were 50 percent less likely to develop retinopathy than those consuming less than that.

Are there other possible eye benefits from eating fish?

The retina is rich in omega-3s, which could also be why some research suggests that eating fish may help reduce the risk of age-related macular degeneration (AMD), the leading cause of blindness among older Americans. A 2016 meta-analysis of previous studies, published in the journal Nutrients, concluded that as fish consumption increased, risk of AMD decreased.

Also see Tips for Smart Seafood Shopping.