Variety among food groups — fruits, vegetables, grains, proteins, dairy and healthy fats — as well as within each food group allows for the greatest abundance of nutrients and phytochemicals in your diet. If you eat three pieces of fruit a day, make one of them citrus for the high vitamin C content and the lignans (a prebiotic fiber) in the white fibrous sections of the fruit. Your second fruit should be a berry for its high anthocyanin and carotenoids content, important cancer-fighting phytochemicals. Then choose your third from among the wide variety of other fresh fruits available seasonally in your market. Susan Kleiner, PhD, RD, is an international columnist and a speaker on the subjects of nutrition, sports and fitness.