Not that you should look to cartoon characters for food guidance, but Popeye was onto something here. Spinach is a serious energy booster, with high levels of iron, which brings fresh oxygen to your cells via your bloodstream, and even some calcium too, for bone health. This leafy green is also high in vitamins A, C, and K, and minerals like potassium and magnesium, and one study showed that spinach may help obliterate prostate cancer cells. It's so low in calories (2 per leaf), you don't have to worry about putting your waistline at risk either, says Silber. Compared to today's popular greens, spinach matches kale's nutrition, but tastes less bitter. And its vitamin and mineral content easily beats kale.