A medium banana (about 7 inches long, 118 grams) contains 105 calories, 27 grams of carbohydrates, 3 grams of fiber, 14 grams of sugar, and 1 gram of protein. It has essentially no fat. But the calorie and sugar numbers only tell part of the story, because the type of carbohydrate in a banana shifts dramatically depending on ripeness.
Full Nutrient Breakdown
Here’s what you get from one medium banana:
- Calories: 105
- Carbohydrates: 27 g
- Dietary fiber: 3 g
- Total sugars: 14 g
- Protein: 1 g
- Potassium: 422 mg (about 10% Daily Value)
- Vitamin B6: 0.43 mg (over 30% DV)
- Vitamin C: 10 mg (over 10% DV)
- Magnesium: 32 mg (about 10% DV)
The standout micronutrient is vitamin B6. A single banana delivers more than 30% of your daily needs, which is unusually high for a piece of fruit. B6 helps your body convert food into energy and plays a role in immune function and brain development. The potassium content is what bananas are famous for, and 422 mg is a meaningful contribution toward the 2,600 to 3,400 mg most adults need daily.
How Ripeness Changes the Nutrition
The calorie count on a banana stays roughly the same whether it’s green or spotted brown, but the composition of those calories changes completely. A green banana is 70 to 80% starch by dry weight, and much of that is resistant starch, a type of carbohydrate your small intestine can’t break down. It passes through to your large intestine, where gut bacteria ferment it. This makes green bananas behave more like a high-fiber food, keeping blood sugar relatively stable and promoting a longer feeling of fullness.
As the banana ripens, enzymes convert that starch into simple sugars: sucrose, glucose, and fructose. By the time a banana is fully yellow with brown spots, it contains only about 1% starch. The 14 grams of sugar listed on nutrition labels reflects a ripe banana. A green one tastes starchier and less sweet because it literally contains less sugar at that point.
Blood Sugar Impact
Bananas score between 42 and 62 on the glycemic index, depending on ripeness. A slightly underripe banana sits around 42, while a fully ripe one reaches about 62. For context, anything at or below 55 is considered low glycemic, meaning it won’t cause a sharp spike in blood sugar. A ripe banana crosses just above that threshold into the medium range.
Glycemic load, which factors in the actual amount of carbohydrate per serving, gives a more practical picture. A ripe banana has a glycemic load of about 13, which is moderate. An underripe banana comes in at roughly 11. Both numbers are close to the low cutoff of 10, which means bananas raise blood sugar gradually compared to foods like white bread or sugary drinks. The resistant starch in less-ripe bananas slows digestion further, which is why some people who are watching their blood sugar prefer bananas that are still slightly firm.
Banana Size Matters More Than You’d Think
The standard nutrition label is based on a medium banana at 118 grams, but bananas vary a lot in size. A small banana (about 6 inches) weighs closer to 100 grams and has roughly 90 calories and 23 grams of carbs. A large banana (8 to 9 inches) can weigh 135 grams or more, pushing the count to around 120 calories and 31 grams of carbs. If you’re tracking macros or managing carbohydrate intake, the difference between a small and large banana is nearly a third more carbs.
Antioxidants in Banana Pulp
Bananas contain dopamine in their flesh, not as a brain chemical (it doesn’t cross the blood-brain barrier when eaten) but as a potent antioxidant. Research published in the Journal of Agricultural and Food Chemistry found that banana pulp contains 2.5 to 10 milligrams of dopamine per 100 grams, with concentrations varying by ripeness stage. In lab tests, this dopamine showed strong free-radical scavenging activity, comparable to some of the most effective plant-based antioxidants. This is one reason bananas contribute to overall antioxidant intake even though they don’t have the vivid pigments typically associated with antioxidant-rich fruits like berries.
How Bananas Compare to Other Fruits
At 105 calories, a banana is on the higher end for fruit. An apple has about 95 calories, an orange about 62, and a cup of strawberries around 50. The trade-off is that bananas pack significantly more potassium and vitamin B6 than most common fruits. They’re also one of the most portable, shelf-stable options available, which is why they remain a go-to snack for athletes and anyone who needs quick energy without preparation.
The 27 grams of carbohydrate in a banana is also higher than most fruits per serving. If you’re on a low-carb diet, that number is worth knowing. But for most people, the fiber, resistant starch (in less-ripe bananas), and micronutrient density make bananas a solid nutritional choice. The sugars in a banana come packaged with fiber and water, which slows absorption compared to the same amount of sugar from processed foods.