One medium ripe banana has around 110 calories, 0 gram of fat, 1 gram of protein, 28 grams of carbohydrate, 15 grams of naturally occurring sugar, 3 grams of fiber, and 450 milligrams of potassium. Bananas are a good source of vitamin B6, manganese, magnesium, and zinc. Almost half of the calories in a banana come from carbohydrates. They're high in starch with some fruit containing up to 10% starch. Most of the remaining 50% comes from fat with less than 1% from protein. That's why they contain so much energy-rich food that can't be used by your body once you've eaten it. Bananas are a good source of vitamins B6 and K, magnesium, and potassium. They also have some calcium but only if you eat a lot of dairy products. No evidence has been found that eating bananas can cause any health problems. However, anyone on a diet should avoid eating too many bananas as they can fill you up without giving you much nutrition. The most common allergens found in bananas include latex proteins, pollen, weed seeds, melons, citrus fruits, and vegetables such as corn, papaya, and pine trees. If you have allergies or asthma, it might not be a good idea to eat bananas because they can trigger an allergic reaction or attack.