Popeye’s secret weapon is not iron, but the nitrates found in spinach, say Swedish researchers from the Karolinska Institute. They found that eating 300 grams (close to 1½ cups) of spinach per day reduces the amount of oxygen needed to power muscles. The nitrates act as “a fuel additive for your muscles—it makes them run much more smoothly,” said lead scientist Dr. Eddie Weitzberg. They do so by helping increase the efficiency of mitochondria, the part of the cell that is responsible for fueling cell activity and growth. The effects are apparent after only three days of eating spinach. Nitric oxide has also been known to open blood vessels and lower blood pressure.