Maybe do you like to eat tuna? Fatty tuna is the most popular food in Japanese sushi restaurants. But it has a health issue: mercury.
Mercury is a kind of heavy metal which is potentially harmful to human. In Japan, thousands of people were killed by Minamata disease which was due to mercury intoxication.
And due to the food-chain, some kind of fish like tuna, shark, and swordfish contain a significant amount of mercury compared to others. Eating such fish leads to taking mercury excessively. Especially pregnant women are encouraged to refrain from eating tuna more than a couple of piece in a day.
In addition, a recent study suggests that taking mercury is relevant to cause amyotrophic lateral sclerosis (ALS). ALS is one of the neurodegenerative diseases hard to treat.
International Business Times: High-mercury seafood like swordfish linked to incurable ALS
In real, ALS is not a common disease. Its prevalence rate is one per ten-thousand. Most people may not be willing to abandon tuna for avoiding ALS.
We should be aware of the risks in daily meal. But you need not avoid any particular foods. A balanced diet is essential.