Pound for pound, spinach provides more nutrients than any other food. The nutrients in this leafy green include vitamin K, vitamin A, manganese, folate, magnesium, iron, vitamin C, vitamin B2, calcium, potassium, and vitamin B6. When it comes to cardiovascular conditioning its high magnesium and iron content increase circulation of oxygen in the blood, which is crucial for optimal performance. Spinach also boasts antioxidants vitamin A and C which can counter balance the oxidative stress of a strenuous workout. Tip: To unlock the iron content of spinach bound, cook your spinach on a medium to high heat to obtain all the nutritional benefits.