A medium banana (about 118 grams) has 105 calories and roughly 1.3 grams of protein. That makes bananas a solid quick-energy snack, though not a meaningful protein source on their own. Here’s what else is worth knowing about their nutritional profile.
Calories and Protein by Size
Banana size varies more than most people realize, and so does the calorie count. A small banana (about 100 grams) comes in around 90 calories with just over 1 gram of protein. A medium banana, the standard reference size at 118 grams, delivers 105 calories and 1.3 grams of protein. A large banana (around 136 grams) bumps up to roughly 121 calories and 1.5 grams of protein.
For context, a medium apple has about 95 calories and essentially zero protein. So bananas are slightly higher in calories but offer a small protein edge, plus less sugar (14 grams versus 19 grams in an apple).
Where the Calories Come From
Nearly all of a banana’s calories come from carbohydrates, about 27 grams in a medium fruit. The interesting part is that the type of carbohydrate shifts dramatically depending on ripeness. A green, unripe banana contains around 21 grams of starch per 100 grams, much of it resistant starch that your body can’t fully digest. By the time that banana is spotted and soft, the starch drops to roughly 1 gram per 100 grams, having converted almost entirely into simple sugars.
This means a green banana and a brown-spotted banana have similar total calories on a nutrition label, but your body processes them differently. The resistant starch in a greener banana acts more like fiber, passing through your upper digestive tract undigested. A ripe banana delivers its energy faster because those sugars are immediately available.
Fiber Changes With Ripeness
Standard nutrition databases list about 3 grams of fiber per medium banana regardless of ripeness. But newer measurement methods tell a more nuanced story. A study published in PLOS One found that when resistant starch is counted as fiber (which it functionally is), a slightly unripe banana contains about 5.9 grams of fiber, a ripe banana about 4.4 grams, and an overripe banana only about 2.2 grams.
If you’re eating bananas partly for their fiber content, choosing them a little on the green side roughly triples the functional fiber you’re getting compared to an overripe banana.
Glycemic Index Is Lower Than You’d Think
Bananas have a reputation as a high-sugar fruit, but their glycemic index is actually low. According to Harvard’s Nutrition Source, ripe bananas score 51 on the glycemic index, and slightly underripe bananas come in even lower at 42. Their glycemic load, which accounts for actual portion size, is a moderate 13 for ripe and 11 for underripe. For comparison, anything under 55 on the glycemic index is considered low, and a glycemic load under 10 is low while 11 to 19 is moderate.
The fiber and resistant starch help slow sugar absorption, which is why bananas don’t spike blood sugar the way their sweetness might suggest.
Why Banana Protein Doesn’t Count for Much
At 1.3 grams per medium fruit, banana protein is negligible in the context of daily needs (most adults need 50 to 60 grams minimum). That said, banana protein does contain all ten essential amino acids. Certain varieties, like red bananas, even meet World Health Organization criteria for an “ideal” amino acid ratio. The quality is fine; there’s just very little of it.
If you’re pairing a banana with a protein source, think peanut butter (7 grams per two tablespoons), Greek yogurt (15 to 20 grams per cup), or a handful of almonds (6 grams per ounce). Those combinations turn a banana from a pure carb snack into something more balanced.
Key Nutrients Beyond Calories and Protein
Bananas are best known for potassium, delivering about 422 milligrams per medium fruit, roughly 9% of the daily value. Potassium helps regulate fluid balance and supports normal blood pressure. They’re also a strong source of vitamin B6, providing about 25% of the daily value in a single banana. B6 plays a role in energy metabolism, immune function, and brain health. You’ll also get a modest dose of vitamin C and magnesium.
- Potassium: ~422 mg (9% DV)
- Vitamin B6: ~0.4 mg (25% DV)
- Vitamin C: ~10 mg (11% DV)
- Magnesium: ~32 mg (8% DV)
For a fruit that costs about 25 cents and requires zero preparation, that’s a solid micronutrient return. The combination of fast-absorbing carbs, potassium, and B6 is also why bananas are a go-to before or after exercise.