A medium banana packs about 110 calories, 28 grams of carbohydrates, 3 grams of fiber, and 450 mg of potassium, making it one of the most nutrient-dense grab-and-go fruits available. Beyond those headline numbers, bananas deliver a surprisingly broad range of vitamins, minerals, and plant compounds that support everything from heart health to digestion.
Calories and Macronutrients
Bananas are primarily a carbohydrate source. A medium banana contains about 28 grams of carbs, 15 grams of naturally occurring sugar, 3 grams of fiber, and just 1 gram of protein with essentially no fat. At roughly 110 calories, that puts them in the same ballpark as a small apple or a slice of bread.
The type of carbohydrate shifts dramatically as a banana ripens. Green, unripe bananas are high in resistant starch, a form of starch your body can’t fully digest in the small intestine. This starch behaves more like fiber, feeding beneficial gut bacteria rather than spiking blood sugar. As the banana yellows and develops brown spots, that resistant starch converts into simple sugars, which is why ripe bananas taste sweeter and are easier to digest. If you’re looking for a lower glycemic option, greener bananas are the better pick.
Potassium: The Standout Mineral
The 450 mg of potassium in a medium banana is about 10% of the daily value. Potassium is an electrolyte that helps regulate fluid balance and keeps your heart beating in a steady rhythm. It also counteracts the blood-pressure-raising effects of sodium. Most adults fall short of the recommended potassium intake (around 2,600 to 3,400 mg per day depending on age and sex), so a banana at breakfast or as a snack makes a meaningful dent in that gap.
Potassium also plays a role in muscle contraction, which is why bananas are a staple for athletes trying to prevent cramps during or after exercise.
Vitamin B6 and Energy Metabolism
Bananas are one of the richest fruit sources of vitamin B6. A standard dessert banana provides about 18% of the daily value per 100-gram serving. This vitamin is involved in more than 100 enzyme reactions in your body, most of them related to protein metabolism. It helps break down amino acids from the food you eat and is essential for forming hemoglobin, the protein in red blood cells that carries oxygen throughout your body.
Vitamin B6 also supports brain function by contributing to the production of neurotransmitters like serotonin and dopamine. Adults aged 19 to 50 need about 1.3 mg per day, and a single banana covers a significant portion of that.
Other Vitamins and Minerals
Beyond potassium and B6, bananas supply a handful of other micronutrients in modest but useful amounts. Per 100 grams of a standard dessert banana:
- Vitamin C: 15% of the daily value. Supports immune function and helps your body absorb iron from plant foods.
- Magnesium: 7% of the daily value. Involved in muscle and nerve function, blood sugar regulation, and bone health.
- Provitamin A: Only about 1% of the daily value in regular yellow bananas, though plantains offer far more (23% of the DV).
None of these alone would meet your daily needs, but they add up alongside the other fruits and vegetables in your diet. Bananas are especially useful because people actually eat them consistently, which matters more for long-term nutrition than any single serving’s numbers.
Antioxidants and Plant Compounds
Bananas contain a wider range of protective plant compounds than most people realize. The pulp contains several types of phenolic acids, including gallic acid, ferulic acid, and catechins, all of which act as antioxidants by neutralizing unstable molecules that can damage cells. Quercetin, a flavonoid also found in onions and berries, supports cardiovascular health by promoting healthy blood flow.
Bananas also contain dopamine and serotonin, though not in a form that crosses the blood-brain barrier to affect your mood directly. Instead, the dopamine in banana pulp functions as an antioxidant, helping protect LDL cholesterol from oxidation, a process linked to artery damage. Plant sterols like beta-sitosterol and campesterol, also present in bananas, may help reduce cholesterol absorption in the intestines.
One compound worth noting: unripe banana pulp contains leucocyanidin, a flavonoid that has shown significant protective effects against stomach ulcers in research settings. This is part of why green bananas have a long history of use in traditional medicine for digestive complaints.
Fiber and Digestive Benefits
The 3 grams of fiber in a medium banana comes from a mix of soluble and insoluble types. Ripe bananas are higher in pectin, a soluble fiber that absorbs water and helps keep stool soft. Green bananas, as mentioned, are rich in resistant starch, which passes through your upper digestive tract intact and ferments in the large intestine. That fermentation produces short-chain fatty acids that nourish the cells lining your colon.
This shift in fiber composition means bananas can be helpful at different ripeness stages for different digestive needs. Ripe bananas are gentle on the stomach and often recommended when recovering from stomach illness. Green bananas may offer more prebiotic benefits for long-term gut health, though some people find them harder to digest due to the higher starch content.
How Banana Varieties Compare
The standard yellow Cavendish banana you find in most grocery stores is just one variety. Plantains (cooking bananas) have a notably different nutritional profile. Per 100 grams, plantains contain 122 calories and 32 grams of carbs compared to 89 calories and 23 grams of carbs for dessert bananas. Plantains also deliver significantly more vitamin C (31% of the daily value versus 15%) and dramatically more provitamin A (23% versus just 1%).
Potassium is slightly higher in plantains at 14% of the daily value per 100 grams, compared to 10% in dessert bananas. Vitamin B6, on the other hand, is marginally higher in regular bananas (18% versus 15%). Protein, fat, and magnesium are nearly identical between the two. The practical takeaway: if you cook with plantains regularly, you’re getting a meaningful boost in vitamins A and C that yellow bananas don’t provide.