Scientists have shown that blueberries are loaded with compounds (phytonutrients) that may help prevent chronic diseases, such as heart disease, diabetes and some cancers. Blueberries may also improve short-term memory and promote healthy aging. Blueberries are a low-calorie source of fiber and vitamin C — 3/4 cup of fresh blueberries has 2.7 grams of fiber and 10.8 milligrams of vitamin C.