Fish can be an excellent part of a healthy diet, providing important nutrients like omega-3 fatty acids, which can reduce the risk of diseases such as cancer, Alzheimer’s, cardiovascular disease, dementia, age-related macular degeneration, and rheumatoid arthritis, among others. However, there are certain fish that should never be eaten. Unfortunately, due to human industrial activity, such as coal-fired electricity generation, smelting, and waste incineration, large amounts of mercury end up in our waterways and, consequently, in the fish that inhabit them. As this mercury enters the marine food chain, it bioaccumulates.

This means that when smaller fish are consumed by gradually larger fish, the mercury concentration at each level increases. Consuming too much mercury can be harmful to health and cause mercury poisoning. For this reason, the U.S. Food and Drug Administration (FDA) and the U.S. Environmental Protection Agency (EPA) have published guidelines on the amount of mercury that humans can safely ingest, and the nonprofit Environmental Defense Fund (EDF) offers suggestions on which fish should not be consumed.

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

Researchers at Wake Forest University School of Medicine say tilapia is one of the most consumed fish in the United States. The problem? It contains very low levels of beneficial omega-3 fatty acids and, even worse, very high levels of inflammatory omega-6 fatty acids.