Popeye had it right:!

Popeye's taste for a can of spinach before a fight has a genuine scientific basis, researchers have found: the leafy green vegetable really can boost your muscle power.

It was thought the iron content of spinach accounted for its status as a superfood. But researchers at the Karolinska Institute in Sweden have found that the inorganic nitrate it contains is the secret of its strength-giving property.

Source - Independent