Banana Nutritional Facts: Sugar, Carbs, and Glycemic Index

Banana are a great source of nutrients, but can have a high glycemic index.

Bananas are a very good source of vitamin B6 and a good source of vitamin C, potassium, and manganese. One medium banana has 17 percent of your daily value of vitamin C, a vitamin which helps you grow and repair tissue as well as heal wounds and maintain bone and dental health. Vitamin C also helps the body make collagen, an important protein for making skin, cartilage, tendons, ligaments, and blood vessels.

Green, or unripe, bananas also contain resistant starch, which has been shown to contribute healthy bacteria in our colons. 

In addition to having approximately 1.3 grams of protein, a medium-sized banana also has quite a bit of sugar. If you are following a low-carb diet, you may want to limit how many bananas you eat and measure your portions since a medium-sized banana is not very big. In fact, most store-bought bananas are much larger.

While it may not seem appealing, a banana's peel is edible. Banana peels are very nutritious and contain high levels of vitamin B6, B12, magnesium, and potassium. Banana peels are not as sweet as the banana fruit but can be eaten virtually the same way you would eat the inside of a banana. Although you can eat the peel raw, most people prefer to cook it.

Carbohydrate, Fiber, and Sugar Counts for Bananas

  • ½ cup sliced bananas: 15 grams effective (net) carbohydrate, 2 grams fiber, 9 grams of sugar, and 67 calories.
  • 1 medium banana (7 inches to 7¾ inches long): 27 grams effective (net) carbohydrate, 3.1 grams fiber, 14 grams of sugar, and 105 calories.
  • 1 large banana (8 inches to 8 and 7/8 inches long): 31 grams effective (net) carbohydrate, 3.5 grams fiber, 17 grams of sugar, and 121 calories.
  • 1 extra-large banana (9 inches or longer): 35 grams effective (net) carbohydrate, 4 grams fiber, 19 grams of sugar, and 135 calories.

    Glycemic Index for Bananas

    The glycemic index (GI) of bananas depends on how ripe the bananas are. A lot of the carbohydrate in green bananas comes in the form of a kind of resistant starch which we lack the enzyme to digest. As the fruit ripens, the starch is converted into readily available sugars.

    One study of "under-ripe" bananas came up with a glycemic index of 30. One of "slightly under-ripe bananas" that were "yellow with green sections" produced a GI of 42, while another of "over-ripe" bananas was 52. However, most studies of bananas haven't specified the ripeness and have come up with GIs ranging from 46 to 70. An average of 52 is usually assigned to bananas.

    Glycemic Load of Bananas

    • ½ cup of sliced banana: 6
    • banana (7 inches to 7¾ inches long): 10

    Storing Bananas

    Did you know that it is a myth that bananas should always be kept at room temperature? The banana industry has been trying unsuccessfully to correct this misinformation for years. Although banana skins will turn black in the refrigerator, the fruit will spoil less quickly if it's refrigerated.

     

    Sources:

    USDA National Nutrient Database for Standard Reference, Release 28.

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