Fresh-Water Fish Contain Biotoxins—Here’s the Best Way to Ged Rid of Them

We’re taught that steaming vegetables, fish, and everything in between is healthier than, say, dumping broccoli florets into a boiling water bath and letting all those good vitamins—fiber, B6, and potassium, to name a few—seep out into the H2O. And new research suggests that when it comes to fish, this couldn’t be more true: streaming tilapia and other filets keeps dangerous toxins from entering your body.

Researchers from the University of Seville took a look at whether steaming fish or boiling fish filets could better reduce cylindrospermopsin, a cyanotoxin found in some of the most eaten freshwater fish, such as tilapia. They found that while boiling fish does reduce the toxin—by about 18 percent, in fact—steaming the filets reduced it even more, to a rate of about 26 percent. What’s more, biotoxins also pass into the steaming water and avoid our bodies almost entirely—which is a very good thing.

Cylindrospermopsin impacts animals’ organs, including the liver, kidneys, heart, intestines, lungs, and brain. In humans, cylindrospermopsin can be drank, ingested, or aspirated—and symptoms include headaches, diarrhea, nausea, abdominal pain, dehydration, fatigue, dry eyes, and even kidney damage. According to the researchers, the cyanotoxin is transferred to food from water that contains it, so it can be found in everything from plant-based foods to cereals, fish, and shellfish.

“It is fundamental to continue investing research resources in this area, as the real exposure [of cylindrospermopsin] to consumers is not known, and therefore the risk is also unknown,” the researchers wrote in their study, published in Food Control.

Until then, if you don’t want to take the risk of ingesting any more of this cyanotoxin than necessary, the report suggests you steam your fish for at least two minutes. And be sure to throw out any steam water you use in your cooking—think: don’t use it for stocks, or to make a sauce—as it will have absorbed the toxin itself. The researchers say their next steps will be to test the results of other common cooking methods like grilling and microwaving in the future.