Also in health news, pregnant women have often been told to increase their intake of fish for the benefit of the babies. But according to a recent U.S. study, they had better stay away from tuna, which has been found to contain high levels of mercury. And its consumption during pregnancy can lead to birth defects and other complications.

While it is very common to hear that eating fish makes smart babies, the concept is challenged by a recent US study, which claims that consuming too many tuna cans can lead to negative brain development of fetus.

The study says that tuna cans of large fish such as longfin tuna and oil fish actually contain mercury, a heavy metal, which is very toxic.

The key is in the food chain.

Medium-sized fish eat small fish, they end up becoming food of large tuna.

Finally, they are food for human.

Eating too much of mercury-containing tuna may affect brain development of fetus or children.

According to local doctors, eating seven pieces of raw fish or a tunafish can per week is considered overconsumption.

But any amount less than that should be fine.

If you want to improve your nutrition, smaller fish is a better choice.