Pregnant women who eat fish at meals three times a week may be providing their children with brain benefits that will last for years, two new studies suggest.

Spanish scientists who tracked almost 2,000 mother-child pairs from the beginning of pregnancy through the next five years found brain function in children whose mothers ate the most fish while pregnant was improved over that of children whose mothers ate the least fish.

Meanwhile, Japanese researchers conducting a study at the Tohoku University's School of Medicine fed pregnant rats a diet that was rich in omega-6 but poor in omega-3, mimicking ratios most commonly found in human diets around the world.

Omega-6 is more commonly contained in seed oils, while omega-3 is almost exclusively found in fish; both are termed essential fatty acids because the body cannot generate them internally and they must be acquired through diet.

The researchers report the diet poor in omega-3 resulted in the rats producing offspring with smaller brains and signs of abnormal emotional behavior when they reached adulthood.

Because a baby's brain development is largely completed while it is in the womb, the brain is more susceptible to dietary deficits than other organs, the researchers point out.

Experts generally recommend a diet with a 1:1 balanced ratio of omega-6 to omega-3, but the average American's diet is often skewed heavily toward omega-6, sometimes as much as 16:1, experts say.

A concern over mercury poisoning is often cited as one reason fish is not as prevalent in the American diet as it should be, they say.

That concern is taken into account in the U.S. Food and Drug Administration's recommendation that pregnant women consume eight to 12 ounces of fish weekly.

In comparison, the European Food Safety Authority recently announced a recommendation of five to 21 ounces of fish weekly during pregnancy.

"Seafood is known to be an important source of essential nutrients for brain development, but at the same time accumulates mercury from the environment, which is known to be neurotoxic," Jordi Julvez of the Center for Research in Environmental Epidemiology in Barcelona, lead author of the Spanish study, acknowledges.

However, even when women consumed 21 ounces of fish weekly during pregnancy, there was no sign that mercury or any other pollutants associated with fish were having a negative effect that offset apparent benefits, the Spanish team says.

"I think that in general people should follow the current recommendations," Julvez says. "Nevertheless this study pointed out that maybe some of them, particularly the American ones, should be less stringent."