Wake Forest researchers say popular fish contains potentially dangerous fatty acid combination

"The ratio of arachidonic acid (AA) to very long-chain n-3 PUFAs (EPA and DHA) in diets of human beings appears to be an important factor that dictates the anti-inflammatory effects of fish oils," the researchers write. They cite numerous studies, including a recent one that predicts "that changes in arachidonic acid to EPA or DHA ratios shift the balance from pro-inflammatory [agents] to protective chemical mediators … which are proposed to play a pivotal role in resolving inflammatory response" in the body.

For their study, the authors obtained a variety of fish from several sources, including seafood distributors that supply restaurants and supermarkets, two South American companies, fish farms in several countries, and supermarkets in four states. All samples were snap-frozen for preservation pending analysis, which was performed with gas chromatography.

The researchers found that farmed tilapia contained only modest amounts of omega-3 fatty acids – less than half a gram per 100 grams of fish, similar to flounder and swordfish. Farmed salmon and trout, by contrast, had nearly 3 and 4 grams, respectively.

At the same time, the tilapia had much higher amounts of omega-6 acids generally and AA specifically than both salmon and trout. Ratios of long-chain omega-6 to long-chain omega-3, AA to EPA respectively, in tilapia averaged about 11:1, compared to much less than 1:1 (indicating more EPA than AA) in both salmon and trout.

The article notes that "there is a controversy among scientists in this field as to the importance of arachidonic acid or omega-6:omega-3 ratios vs. the concentration of long-chain omega-3 alone with regard to their effects in human biology." Those issues are raised in an editorial in the same issue of the Journal.

The Wake Forest article anticipates that criticism and notes that one human study involving AA showed a probable gene-nutrient connection to coronary heart disease in a specific group of heart disease patients. In another study, four subjects were removed after consumption of high amounts of AA due to concerns about the effect of the acid on their blood platelets.

Floyd H. "Ski" Chilton, Ph.D., professor of physiology and pharmacology and director of the Wake Forest Center for Botanical Lipids, is the senior author of the Journal article. He said that in next month's Journal, he will publish a rebuttal to this month's editorial.

"We have known for three decades that arachidonic acid is the substrate for all pro-inflammatory lipid mediators," Chilton said in an interview. "The animal studies say unequivocally that if you feed arachidonic acid, the animals show signs of inflammation and get sick.