Grapefruits get the thumbs up from every nutritionist, myself included. I love to kick off my day with a pink grapefruit that I peel thickly, cut into segments and add a thin sprinkle of brown sugar. Nothing nicer before my muesli! Like other citrus, grapefruits are packed full of vitamin C, providing an entire day's needs in just half an grapefruit. This vitamin can enhance iron absorption, speed up wound healing and reduce the risk of a heart attack.