Source Of. One serving, or one medium ripe banana, provides about 110 calories, 0 gram fat, 1 gram protein, 28 grams carbohydrate, 15 grams sugar (naturally occurring), 3 grams fiber, and 450 mg potassium.It can help keep your cholesterol and blood pressure in check, and help ease inflammation. Green bananas are full of something called resistant starch. It acts like insoluble fiber, which is the kind that can help keep your bowels working at their best. Resistant starch also helps lower your blood sugar.