The carb composition of bananas changes drastically during ripening.
The main component of unripe bananas is starch. Green bananas contain up to 80% starch measured in dry weight.
Bananas have a relatively low glycemic index (GI) of 42–58, depending on their ripeness. The GI is a measure of how quickly carbs in food enter your bloodstream and raise blood sugar (3).
Bananas’ high content of resistant starch and fiber explains their low GI.
The nutrition facts for 1 medium-sized banana (100 grams) are (1Trusted Source):
Calories: 89
Water: 75%
Protein: 1.1 grams
Carbs: 22.8 grams
Sugar: 12.2 grams
Fiber: 2.6 grams
Fat: 0.3 grams