With government guidelines urging everyone to eat fish twice a week for heart and brain benefits, you might wonder: If two days of fish is good, is eating fish every day even better?
That's a question experts haven't yet completely answered. And it's a little complicated because it's not just a health issue, it's also an environmental one. Simply put, there are probably not enough fish in the sea for everyone to eat seafood all the time.
But, experts say, eating seafood more than twice a week, for most people, can be healthful.
"For most individuals it's fine to eat fish every day," says Eric Rimm, a professor of epidemiology and nutrition and director of in cardiovascular epidemiology at the Harvard School of Public Health. "And it's certainly better to eat fish every day than to eat beef every day."
However, Rimm says, there are some groups — pregnant women, for example — who shouldn't eat certain kinds of fish every day. Larger fish with longer life spans like swordfish and tuna tend to bioaccumulate toxins, such as mercury, he explains.
"And that's not great for a developing fetus," Rimm says. For the same reason, daily consumption of these types of fish is also not good for children, he adds.
Mercury is much less of a problem in smaller fish with shorter life spans, says Theresa Sinicrope Talley, a researcher with the California Sea Grant at the Scripps Institution of Oceanography at the University of California, San Diego.
Mercury won't cause lasting damage in adults, although it can cause temporary neurological effects.
"There are anecdotal reports from places where people eat fish every day of patients complaining of neurological problems, like dizziness or problems concentrating," Rimm says. "Those would be people eating maybe sushi or tuna twice a day. You tell them to stop, and sure enough, the mercury levels go down." When that happens, Rimm says, the symptoms pass.
As for the question of whether eating fish every day is even more healthy than twice a week, the science is still out on that, Rimm says.
"Most of the science isn't looking at daily consumption," he explains. "But many, many studies have shown that those who have it a couple of times a week have a lower rate of fatal heart attacks compared to those who don't eat any."
Scientists attribute most of the heart-healthy benefits of fish to omega-3 fatty acids. These nutrients have also been shown to improve cognition in adults and aid in the brain development of babies.
As for the environmental issues, they're a little thornier. Some experts have suggested that we could empty the seas of fish by 2050 if we increase the amount we eat.
"Even to get people eating fish two times a week we need to ramp up fish farming," Rimm says.
Are farmed fish as nutritious as wild caught ones? "It completely depends on the fish," Rimm says. "In some cases farm raised are healthier because they are fed more omega-3 through their feed than would a wild caught fish."
Indeed, fish farms are on the rise all around the world, says Daniel D. Benetti, professor and director of aquaculture in the department of ecosystems & society at the University of Miami. "In 2015 we passed a major milestone," says Benetti. "We are producing more seafood than beef: 66 million metric tons of seafood versus 63 million metric tons of beef."
Fish farms are also becoming more environmentally friendly. Until now, one of the biggest knocks against farmed fish concerned what farmers fed the fish - namely, other fish.
But that's changing and it's economics that drives the change, Benetti says.
Researchers have been trying to devise pelleted feeds that contain more soy than fish. As it turns out, that's a whole lot cheaper than feeding 100 percent fish meal and oil, Benetti says. The trick is to make the pellets taste good. "We fool the fish into thinking they are eating all fish meal and oil," he says.
Still, fish farms aren't the whole solution, says Talley.
Consumers should also consider broadening their gustatory horizons to include smaller fish, shellfish, mollusks, and even seaweed, she says, giving them the additional benefit of a more diverse diet—which is also healthier.