A fresh banana gets about 75 percent of its weight from water, according to the USDA. The drying process removes about 96 percent of this water content, making dehydrated bananas a far more concentrated source of calories and nutrients than the source fruit. Ounce for ounce, dehydrated bananas are about four times higher in fiber, potassium, carbohydrates, sugar and calories than the fresh variety. They're only slightly higher in vitamin B-6, however, largely because it's a water-soluble vitamin. Dehydrated bananas are actually about 20 percent lower in vitamin C, a water-soluble vitamin that's particularly sensitive to heat.