Fish can be an excellent part of a healthy diet, providing important nutrients like omega-3 fatty acids which can lower your risk for diseases like cancer, Alzheimer’s, cardiovascular disease, and dementia, age-related macular degeneration, and rheumatoid arthritis, among others. However, there are certain fish you should never eat. Unfortunately, because of human industrial activity like coal-fired electricity generation, smelting, and the incineration of waste, large amounts of mercury are ending up in our waterways, and subsequently, the fish that swim in them. As this mercury gets into the marine food chain, it “bioaccumulates.”

This means that when smaller fish get eaten by gradually larger fish, the concentration of mercury at each level becomes greater. Consuming too much mercury can be not safe to your health, and cause mercury poisoning. For this reason, the US Food and Drug Administration (FDA) and the US Environmental Protection Agency (EPA) have issued guidelines regarding how much mercury is safe for humans to ingest, and the non-profit Environmental Defense Fund (EDF), provides suggestions for which fish you shouldn’t eat.

1. Tilapia

Did you know that in some regards, eating tilapia is worse than eating bacon? In fact, the shift to eating more farmed fish like tilapia is leading to highly inflammatory diets, according to a 2008 study published in the Journal of the American Dietetic Association.

Wake Forest University School of Medicine researchers say tilapia is one of the most widely consumed fish in America. The problem with that? It contains very low levels of beneficial omega-3 fatty acids and, perhaps worse, very high levels of inflammatory omega-6 fatty acids.