A medium-sized banana, roughly seven to eight inches long, contains about 105 calories. That number comes almost entirely from carbohydrates, with virtually no fat and only a gram or so of protein. But the real answer is more interesting than a single figure, because the calories you actually absorb from a banana depend on its size, how ripe it is, and what your body does with the starch inside it.
Calories by Size
Bananas sold at grocery stores vary quite a bit in length and weight, and the calorie difference between a small banana and a large one is meaningful if you eat one or two every day. A banana under six inches long weighs around 80 grams of edible flesh and delivers roughly 72 calories. A small banana in the six-to-seven-inch range runs about 90 calories. The standard medium banana used for most nutrition labels weighs around 118 grams and lands at about 105 calories. Large bananas approaching nine inches carry around 121 calories, and the occasional extra-large specimen can reach 135 calories or more. The peel accounts for about 35 percent of the total weight, so if you weigh a banana on a kitchen scale, you need to subtract a third before estimating the calorie content.
Nearly all of those calories come from carbohydrates. A medium banana delivers around 27 grams of total carbs, including about 3 grams of fiber. The rest is a mix of sugars and starch, the ratio of which shifts dramatically as the fruit ripens.
The Starch-to-Sugar Shift During Ripening
If you have ever noticed that a green banana tastes starchy and chalky while a spotted brown one tastes almost candy-sweet, you have already observed the most important thing about banana calories. As a banana ripens, enzymes break its starch down into simple sugars. A fully ripe banana contains only about 1 percent starch by fresh weight, while its total sugar content sits at roughly 23 percent.1Journal of the Science of Food and Agriculture. Starch and sugar transformation during the ripening of plantains and bananas An unripe green banana, by contrast, can be 15 to 35 percent starch by weight, with very little free sugar.2Horticulture Research. Telomere-to-telomere haplotype-resolved reference genome reveals subgenome divergence and disease resistance in triploid Cavendish banana
This matters because starch and sugar, while both carbohydrates, behave differently in your digestive system. A large portion of the starch in a green banana is resistant starch, a type of carbohydrate that resists digestion in the small intestine and passes through to the large intestine largely intact. Green banana flour, which preserves the unripe composition, contains roughly 30 percent resistant starch on a dry-weight basis, one of the highest concentrations found in common foods.3PubMed Central. Green banana resistant starch: A promising potential as functional ingredient against certain maladies As the banana ripens, that resistant starch drops sharply. One study measuring bananas at different retail ripeness stages found that the starch content dropped by about 9.3 grams per 100 grams between the unripe and slightly ripe stage, with smaller declines continuing as the fruit moved from ripe to overripe.4PubMed Central. Dietary fiber, starch, and sugars in bananas at different stages of ripeness in the retail market
The sugars that replace that starch are mostly glucose, fructose, and sucrose. The same study found that glucose and fructose each jumped by about 5 grams per 100 grams between unripe and slightly ripe, then held relatively steady through the ripe and overripe stages. Sucrose followed a quirky pattern: nearly absent in unripe fruit, it peaked at around 2.5 grams per 100 grams in slightly ripe and ripe bananas, then fell back down in overripe fruit as enzymes continued breaking it into glucose and fructose.4PubMed Central. Dietary fiber, starch, and sugars in bananas at different stages of ripeness in the retail market
Do You Actually Absorb All Those Calories?
The calorie count on a food label is not a direct measurement of how much energy your body extracts. It is an estimate based on a system developed in the late 1800s that assigns standard calorie values to each gram of protein, fat, and carbohydrate. For a banana, the system counts every gram of carbohydrate at four calories, whether that carbohydrate is rapidly digested sugar or resistant starch that passes through you unabsorbed.
Research has shown that these standard conversion factors overestimate the available energy in high-fiber, plant-based foods. A study examining energy availability from different diets found that the standard system overestimated usable calories by up to 11 percent for low-fat, high-fiber diets containing plenty of fruits, vegetables, and cereals.5The American Journal of Clinical Nutrition. Accuracy of the Atwater factors and related food energy conversion factors with low-fat, high-fiber diets when energy intake is reduced spontaneously Since a green banana is essentially a high-fiber, high-resistant-starch food, its true caloric yield is likely lower than what the label says. A ripe banana, with most of its starch already converted to absorbable sugars, would come much closer to the listed number. This means two bananas with the same weight can deliver meaningfully different amounts of usable energy depending on their ripeness.
For most people, the difference is not large enough to worry about. But if you are counting calories closely or managing blood sugar, it helps to know that a firm, slightly green banana delivers fewer absorbable calories than a soft, heavily spotted one.
How Ripeness Changes Blood Sugar Response
The starch-to-sugar conversion has a direct effect on how quickly your blood sugar rises after eating a banana. A study in people with type 2 diabetes compared blood glucose responses to under-ripe and over-ripe bananas. The under-ripe banana produced a glycemic index of about 43, while the over-ripe banana came in at 74, a substantial jump.6PubMed. Influence of ripeness of banana on the blood glucose and insulin response in type 2 diabetic subjects For comparison, white bread in the same study produced a significantly higher blood glucose area than either banana, but the gap between the two ripeness stages was large enough to matter for anyone watching their glycemic load.
The insulin responses, interestingly, were similar across the board in that study. Under-ripe and over-ripe bananas triggered roughly the same insulin release despite the very different glucose curves. The researchers attributed the low glycemic response of under-ripe bananas to their high starch content, which human digestive enzymes break down slowly.6PubMed. Influence of ripeness of banana on the blood glucose and insulin response in type 2 diabetic subjects
The variety of banana also plays a role. A study measuring estimated glycemic index across several Indian banana varieties found that some varieties reached an estimated GI of 65 to 67 percent while others stayed lower, even at the same ripeness stage.7Food Bioscience. Ripening dependent changes in skin color, physicochemical attributes, in-vitro glycemic response and volatile profiling of banana varieties Most grocery store bananas in North America and Europe are Cavendish, a single cultivar, so variety-based differences are mainly relevant if you shop at specialty markets or live in tropical regions where multiple cultivars are common.
Bananas as Exercise Fuel
Athletes have long used bananas as a mid-workout energy source, and the research backs the practice up surprisingly well. In a study where trained cyclists completed 75-kilometer time trials, eating bananas during the ride produced the same power output, heart rate, perceived effort, and finishing time as drinking a standard carbohydrate sports beverage. Blood glucose and lactate patterns during exercise were also nearly identical between the two conditions, with riders consuming about 150 grams of carbohydrate during each trial.8PLoS ONE. Bananas as an Energy Source during Exercise: A Metabolomics Approach
A follow-up study went further, comparing banana and pear ingestion against water alone during similar 75-kilometer rides. Performance times were about 5 percent faster with bananas and about 3 percent faster with pears compared to water only. Both fruits also reduced cortisol and some inflammatory markers compared to the water-only condition, and they contributed unique plant compounds that increased the blood’s antioxidant capacity.9PubMed. Metabolomics-Based Analysis of Banana and Pear Ingestion on Exercise Performance and Recovery That antioxidant benefit is something a glucose drink or gel cannot replicate.
After exercise, bananas also appear useful for maintaining blood glucose. A trial examining recovery from heavy exertion found that eating bananas during the post-exercise window kept plasma glucose elevated during the first 90 minutes of recovery, while water alone led to a rebound glucose spike after the next meal.10PLOS ONE. Metabolic recovery from heavy exertion following banana compared to sugar beverage or water only ingestion: A randomized, crossover trial For the practical calorie question, this means a banana’s roughly 105 calories are efficiently used during and after activity, performing on par with engineered sports nutrition products.
Beyond Calories: What Else You Get
If you are choosing a banana primarily for its calorie content, you are undervaluing the fruit. A medium banana delivers about 422 milligrams of potassium, which is roughly 9 percent of most adults’ daily target and more than most other common snack foods provide. It also contributes vitamin B6, vitamin C, magnesium, and manganese. The fiber content, around 3 grams per medium banana, puts it roughly in the middle of the fruit category, behind berries and pears but ahead of grapes and watermelon.
Resistant starch, specifically the kind concentrated in greener bananas, does not simply pass through unused. It acts as a prebiotic, feeding beneficial bacteria in the large intestine that produce short-chain fatty acids. A mouse study found that green banana flour enriched beneficial bacterial families and helped restore gut microbiota balance after antibiotic disruption, also improving colonic barrier integrity.11PubMed Central. Green Banana Flour Contributes to Gut Microbiota Recovery and Improves Colonic Barrier Integrity in Mice Following Antibiotic Perturbation Another study, also in mice, showed that green banana flour combined with another dietary fiber source produced a synergistic prebiotic effect and boosted short-chain fatty acid production throughout the colon.12Journal of Functional Foods. Prebiotic effects of a mixture of agavins and green banana flour in a mouse model of obesity These are animal studies, so the effects cannot be assumed identical in humans, but they are consistent with what we know about resistant starch as a prebiotic in human diets.
Plantains and Other Cultivars
There are over a thousand banana cultivars worldwide, and they do not all have the same caloric profile. The Cavendish banana that dominates Western grocery stores is a dessert banana, bred for sweetness. Plantains, which are cooking bananas, are starchier at every stage of ripeness. Even when fully ripe, a plantain retains about 9 percent starch by fresh weight, compared to just 1 percent in a ripe dessert banana. Overripe plantains still hold around 3 percent starch.1Journal of the Science of Food and Agriculture. Starch and sugar transformation during the ripening of plantains and bananas Overripe plantains also accumulate more total sugar than dessert bananas: 27 percent versus 23 percent.
The starch in different cultivars also varies in composition. A study comparing starch from dessert, cooking, and plantain bananas found that resistant starch levels in unprocessed raw starch ranged from about 59 to 66 percent in cooking and plantain types, with substantial differences in granule size and amylose content between cultivars.13PubMed. Exploring differences in the physicochemical, functional, structural, and pasting properties of banana starches from dessert, cooking, and plantain cultivars (Musa spp.) Higher amylose starch tends to resist digestion more stubbornly, so a plantain dish made from a high-amylose cultivar would yield fewer absorbable calories per gram of carbohydrate than a ripe Cavendish banana eaten raw.
In practical terms, a medium-sized plantain contains more total calories than a Cavendish banana, often in the range of 215 to 230 calories, because plantains are larger and denser. But if the plantain is cooked, cooled, and then reheated, some of its starch retrograde and becomes resistant again, reducing the usable energy somewhat. This is the same principle behind the idea that cold leftover rice has fewer absorbable calories than freshly cooked rice.
The Peel Question
Interest in eating banana peels has grown in recent years, partly for sustainability reasons and partly because of claims about their nutritional value. The peel of a banana is not calorie-free. Research on green banana peel flour found it contained about 361 calories per 100 grams and was remarkably high in dietary fiber, at roughly 39 grams per 100 grams, far exceeding the fiber content of the flesh.14SciELO / Brazilian Journal of Food Technology. Design and validation of a nutritional recipe for a snack made of green banana peel flour (Musa paradisiaca) That fiber density means much of the caloric content would not actually be absorbed, again because of the same overestimation issue with standard calorie accounting for high-fiber foods.
Raw banana peel is tough, bitter, and not particularly pleasant to eat. Most culinary applications involve blending it into smoothies, baking it into flour, or cooking it in stews and curries. If you are curious, ripe banana peels are softer and less tannic than green ones. But no one needs to eat the peel for nutritional completeness. The flesh of a ripe banana already provides a well-balanced package of fast-digesting energy, potassium, fiber, and B vitamins. The peel is a bonus for people who want to reduce food waste, not a missing nutritional link.
How Bananas Fit Into a Calorie Budget
Bananas sometimes get a bad reputation in low-carb circles for being “too sugary,” and it is worth putting that in perspective. At roughly 105 calories for a medium fruit, a banana delivers fewer calories than most granola bars, muffins, or handfuls of trail mix. Its sugar content, about 14 grams in a ripe medium banana, is comparable to an apple and lower than a cup of grapes. The difference is that banana sugar arrives alongside potassium, fiber, vitamin B6, and, if the banana is on the greener side, a significant dose of resistant starch that feeds beneficial gut bacteria.
For people managing diabetes, the ripeness advice covered earlier is the most actionable piece: choosing a banana with some green on the peel rather than a heavily spotted one cuts the glycemic response roughly in half. Pairing a banana with a source of protein or fat, like nut butter, slows digestion further. And for anyone using bananas as workout fuel, the evidence is clear that they perform on par with commercial sports nutrition at a fraction of the cost and without artificial ingredients. A banana is about as efficient a package of exercise calories as you can find growing on a tree.