A slice of banana bread contains about 196 calories, 2.6 grams of protein, 32.8 grams of carbohydrates and 6.3 grams of fat, including 1.3 grams of saturated fat. Since banana bread is usually made with refined flour rather than whole-wheat flour, a slice only contains about 0.7 grams of fiber. While bananas are high in folate, vitamin B-6, vitamin C, copper, iron, magnesium and fiber, banana bread is not, since it contains a relatively small amount of banana.