Buy Organic: Spinach

This leafy, green powerhouse is a great source of protein, vitamins A, C, E, and K, thiamin, riboflavin, vitamin B6, folate, calcium, iron, magnesium, phosphorus, potassium, copper, and manganese -- and has about 7 calories a cup. Because spinach binds with iron and calcium, reducing their absorption, enjoy vitamin-C-rich foods such as orange juice, tomatoes, or citrus fruit with spinach to aid absorption.