kiwifruit come out top, even beating nutrient-rich citrus fruit, according to a recent study. Kiwis contain more polyphenols than oranges and grapefruit, and the golden variety contain the most antioxidants, say scientists from Japan\'s Teikyo University. Participants ate three kiwifruit a day, then had their urine tested for antioxidant levels. Researchers say kiwifruit may help prevent the development of diseases caused by oxidative stress, such as heart failure, cancer and Parkinson\'s.