There’s abundant evidence that diets rich in seafood — especially fatty fish — are healthful.
That’s clear from the findings of many dozens of epidemiological (population) studies, and the generally positive outcomes of dozens of clinical studies.
Scientists presume that the health benefits flow from their omega-3s — DHA and EPA — which occur only in fish, shellfish, and algae and perform essential immune and brain functions in the body.
While a few plant foods — e.g., dark leafy greens, avocados, and walnuts — contain very small amounts of an omega-3 fatty acid called ALA, the body must convert it — very inefficiently — into DHA and EPA.
Now, the findings of a Danish study suggest that it’s wise to make seafood — not meat — the major animal-source protein in your diet.
Most evidence suggests that, even in moderation, meat is actively healthful. Rather than condemning meat, the new findings simply suggest that meat should share the stage with seafood more equally than is typical of American tables.
Danish study sees benefit in a seafood-first protein plan
The new study was conducted by researchers at the Technical University of Denmark’s National Food Institute (Thomsen ST et al. 2019).
Importantly, the University of Denmark team employed a new way to analyze the effects of replacing one type of food with another — a method that may be more reliable than the standard statistical tools.
Danish PhD candidate Sofie Theresa Thomsen created the tool used to calculate the total health impact of replacing red and processed meat with fish, up to Denmark’s officially recommended weekly intake of 350 grams of fish.
They chose these two food groups because each category of protein has apparent pros and cons:
So, their clinical study was designed to test whether replacing red and processed meat with fish would improve the Danish participants’ health and health prospects.
Before and after the study, they measured the levels of blood and other biological markers known to predict the risk for heart and other common chronic diseases.
After conducting their analysis of changes in the volunteers’ biological markers for various disease risks, they concluded that replacing some meat with seafood is a good idea.
As they wrote, “The average Dane will gain a health benefit from substituting part of the red and processed meat in their diet with fish … men over 50 and women of childbearing age in particular would benefit from such a change in diet.”
Supporting those findings, a 2016 Danish-Harvard study involving 55,171 women and men aged 50-64 years linked replacement of red meat, poultry, or lean fish with fatty fish to a lower risk of heart attacks (Wurtz AM et al. 2016).
Likewise, a more recent Danish study involving 53,163 participants linked replacement of all red meat — or just processed red meat — with fish reduced the risk of type 2 diabetes (Ibsen DB et al. 2018)
Denmark would gain 7,000 healthy years of life annually
The authors of the Danish study calculated the beneficial and adverse health effects of high-seafood versus the high-meat diets by estimating how many healthy years of life the Danish people would gain or lose, and the associated risks of dying earlier than expected.
As Sofie Theresa Thomsen said about the results of their analysis, “They show that the population can gain up to 7,000 healthy years of life annually, if all adult Danes eat fish in the recommended quantities while at the same time reducing their meat intake. This estimate includes the prevention of approximately 170 deaths from coronary heart disease per year.”
However, as she said, “… the health benefit depends on the type of fish people put on their plates, as well as the age and sex of the persons whose diet is being altered.”
She noted that the greatest health benefit comes from eating only fatty fish such as salmon, albacore tuna, sardines, sablefish, and mackerel — or a mixture of fatty and lean fish such as cod or salmon — because fatty fish contain larger amounts of beneficial omega-3 fatty acids.
Their calculations showed a smaller health gain from eating only lean fish such as cod, sole, and yellowfin tuna.
Greatest benefit seen among men over 50 and women of childbearing age
The study shows large variations in the overall health impact when the red and processed meat gives way to fish.
Everyone over the age of 50 — but the men in particular —as well as women of childbearing age will reap the greatest health benefits from eating 350 grams of fish weekly, of which 200 grams are fatty fish.
This is because men are generally at higher risk of developing cardiovascular disease, which can be reduced by replacing part of the red meat with fish that contain the omega-3s (DHA and EPA) known to help prevent cardiovascular disease.
Sofie Theresa Thomsen added this comment about pregnant women and potential mothers: “In women of childbearing age the health benefit is particularly large because the intake of fish containing healthy fish oils [omega-3s] will not only benefit the women themselves. The health-promoting properties of fish will also have a beneficial effect in the development of their unborn children, which is taken into account in the overall calculations.”
Mercury risks overblown, as usual
Oddly, despite overwhelming evidence that almost all ocean fish is safe for children and pregnant mothers, they calculated "a significant health loss if tuna is the only fish in the diet", because, as they wrote, “tuna is both low in beneficial fatty acids and can have high concentrations of methylmercury.”
Despite that statement, their calculations didn't find that mercury played a significant role in the benefits of eating more seafood: see "Mercury in fish didn’t much matter", below.
Unfortunately, their statement is quite misleading. While some species of tuna (e.g., yellowfin) are low in omega-3s, albacore tuna is extremely rich in both omega-3s and vitamin D.
And a clear preponderance of evidence shows that — excepting the very few low-selenium commercial species like shark, swordfish, tilefish, king mackerel — fetuses are not harmed when mothers eat plenty of seafood.
In fact, seafood-rich maternal diets are linked to better brain performance in young children. (See FDA Analysis Supports More Fish for Moms and Kids and Benefits of Fish to Kids Found to Outweigh Risks.)
In addition, as the team wrote, there’s another upside to eating more fish, and no downside in terms of iron intake: “… the study shows that it is possible to reduce the proportion of Danes who have an insufficient intake of vitamin D significantly by replacing some of the red and processed meat with a mixture of fatty and lean fish. The study also points out that the proportion of Danes with an insufficient intake of dietary iron will not increase despite the lowered meat intake.”
Mercury in fish didn’t much matter
The finding that replacing red and processed meat with seafood brings broad health benefits held true after the researchers accounted for the fact that fish can contain mercury or man-made pollutants like PCBs.
Why would the mercury in ocean fish not reduce the benefits of replacing red or processed meat with seafood?
With very few exceptions — primarily shark, swordfish, tilefish, and king mackerel — the risks of the mercury found in commonly sold ocean fish is very low or nonexistent.
Selenium accounts for the safety of almost all ocean fish. Mercury only harms the nervous system because it binds to the body’s internal stores of selenium, which is a critical component of the body’s own antioxidant system.
Because almost all commercial ocean fish contain more selenium than mercury, it provides enough selenium to restore the amounts “stolen” from it by the mercury in ocean fish.
For more on that topic, see Feds Advise Kids and Pregnant Women to Eat More Fish, Most Fish Rank as Very Safe on New, Selenium-Based Standard, and more articles in the Mercury & Health Issues section of our newsletter archive.
Note: Freshwater fish are riskier, because they are more likely contain more mercury than selenium. The selenium-mercury balance in freshwater fish depends on the selenium content of the surrounding soils, and whether their habitats are located downwind from coal-burning, mercury-emitting power plants. It’s not uncommon to see signs around lakes and rivers in such regions, warning people not to eat the fish.