Healthy Fish Guide: How To Pick And Eat The Healthiest, Greenest Types

We all know that fish can be a great source of heart-healthy lean protein. In fact, according to the Mayo Clinic, swapping in one or two servings of fish as your protein each week can lower heart attack risk by up to one-third. That's thanks to heart-healthy omega-3 fatty acids, which help to reduce inflammation throughout the body, lower triglyceride levels and support brain health, among other benefits. The omega-3s you get from fish -- what are known as long-chain omega-3s, EPA and DHA -- are the most beneficial, according to WebMD.

But that doesn't mean eating fish can't also be fraught with concerns. Many fish species have high levels of the metal mercury -- a dangerous contaminant that can affect the nervous system. Mercury from pollution and that naturally occurs in the atmosphere both settle in our oceans, lakes and streams, where they are consumed by fish and then converted to the toxin, methylmercury. Fish that are high on the food chain consume other contaminated fish, compounding their mercury levels. The primary concern with fish and mercury is in infants and young children, whose developing nervous systems are particularly vulnerable to mercury's effects, but adults who have high exposure levels (an unlikely outcome from eating a few servings of fish) can experience significant central nervous system damage as well. Pregnant and nursing women are advised to be extremely careful about choosing the types of fish to eat.