Most people can enjoy a banana every day without worrying about side effects; in fact, the health benefits far outweigh any downside. A few exceptions exist, however, such as the chance of developing minor gut problems or rare, but more serious allergies. If you’re at risk for potential side effects, be sure to consult your doctor before eating bananas.
Potential Side Effects of Bananas
People with an allergy to latex have a high risk of being allergic to bananas, as well as to avocados, kiwi fruit and chestnuts. All four foods contain the same protein found in latex that causes the allergic reaction. Having a ragweed allergy also increases the chance of being allergic to bananas. This cross-reaction, called oral allergy syndrome, makes your mouth feel itchy or scratchy. The symptoms of oral allergy syndrome go away when the food is swallowed, but latex allergies may cause severe and dangerous reactions.
Bananas contain the amino acid tyrosine, which the body converts into tyramine. Tyramine may trigger migraine headaches in some people, although this doesn’t mean you have to keep bananas out of your diet if you suffer from migraines. Ask your doctor to be sure, because some sources advise limiting consumption to half of a banana daily, while others say bananas are allowed on a low-tyramine diet.
Medications called monoamine oxidase inhibitors interact with tyramine, so also get your doctor’s approval to eat a daily banana if you take MAOIs.
Fiber in Bananas and Gut Reactions
Eating one banana daily isn’t likely to cause gastrointestinal problems like gas, bloating and diarrhea -- and if it does, it’s only temporary -- but be aware that it’s a possibility. One medium banana has 3 grams of dietary fiber, which you need to stay healthy, yet may be enough to cause gas and diarrhea if you’re not used to eating fiber. If you eat fiber throughout the day from other foods like veggies and beans, adding a banana into the mix may be just a bit too much fiber for your GI tract to handle.
In addition to dietary fiber, bananas contain resistant starch. The body usually digests starch into sugar and uses it for energy, but resistant starch is different. It’s just like soluble fiber, which means it passes undigested through the GI tract and is fermented by bacteria in the large intestine. While fermentation supports beneficial bacteria and produces short-chain fatty acids that protect the health of your intestine, it also creates gaseous byproducts that may lead to bloating. Gastrointestinal problems should go away as your body gets used to processing the fiber and resistant starch.
Daily Banana and Blood Sugar
Not long ago, people avoided bananas because the fruit had a bad reputation for being too starchy and spiking blood sugar. But they’re really not that bad. A ripe, yellow banana has a glycemic index score of 51 to 52, reported the American Journal of Clinical Nutrition in 2002. The glycemic index rates foods according to their impact on blood sugar. Any glycemic score of 55 or less indicates a low-glycemic food that doesn’t significantly raise blood sugar.
Eating more than one banana at a time, combining a banana with a high-glycemic cereal like corn flakes or puffed rice, or eating a banana dipped in chocolate, will have a bigger effect. The banana's glycemic index score is close to 56 -- and 56 begins the moderate-glycemic range -- so consuming a banana along with more carbs or added sugar could easily make a difference in blood sugar.
Calorie and Nutrient Considerations
The calories in a banana won’t ruin your diet unless you’ve already reached your maximum daily calorie intake. One medium-sized banana only has 105 calories. Most adults can fit a 105-calorie snack into their daily diet or turn the calories into a nutritious meal by adding Greek yogurt, wheat germ or walnuts, and strawberries. You’ll get 27 grams of carbs, which is great for energy but won’t work well if you’re on a low-carb diet. Also, remember to include bananas in your daily tally if you’re counting carbs.
You only need one banana to gain 22 percent of the daily value of vitamin B-6 and 17 percent of vitamin C. It also provides 16 percent of manganese and 9 percent of potassium. The daily value is based on consuming 2,000 calories daily, so your percentage may vary a little, but you’ll still make a good dent in your daily nutrients by eating one banana daily. Because most Americans don’t get enough vitamin C and potassium, your daily banana may protect your health more than you realize. You need vitamin C for its antioxidant activity and to maintain healthy connective tissues and bones, while potassium helps lower blood pressure and keeps nerves and muscles working.