Unripe bananas, too ripe bananas and sometimes bananas during all ripening stages can cause stomach upset with symptoms such as bloating, flatulence, burping, nausea or diarrhea, headaches, coughing, breathing difficulties, rash and a whole range of other side effects, the most severe being anaphylactic shock. The different side effects of eating bananas can have various causes, from mere sensitivities to the resistant starch in the unripe fruit to an intolerance to the fruit itself or a genuine allergic reaction to certain proteins in the fruit. Even more, certain conditions, gastrointestinal disorders in particular and several food allergies, may increase the chances of experiencing side effects after eating bananas.
Bananas: what are the side effects of eating them? Depending on the ripening stage which is a cause for important nutritional changes in the nutrient profile of the fruit and existing conditions that may increase the likelihood of adverse reactions, the following side effects are possible:
Unripe bananas side effects: indigestion, abdominal cramps, acid reflux, heartburn, nausea, vomiting sensation, irritation of the stomach and accentuated gastritis symptoms, burping, flatulence, diarrhea and general stomach upset, sometimes constipation. Eating an unripe banana can cause a person to be unable to eat anything for several hours. Although extremely rare, there is also a risk of intestinal blockage if you eat too many very unripe bananas. Also read Are Unripe Bananas Bad for You?
Cause: The main reason why unripe bananas are bad for you is because they have a different dietary fiber profile, more specifically they contain overall more fiber (a.k.a. indigestible plant material) than ripe bananas and resistant starches (which are also a type of indigestible plant material). The greener and firmer the fruit, the more fiber it has and the more difficult to digest it is, meaning it will require the stomach to put in more effort, more time and maybe produce more stomach juices in order to partially digest the unripe fruit and prepare it for the intestinal tract. This alone represents a source of gastrointestinal upset for some people with more sensitive stomachs, with gastritis or stomach ulcers or simply not used to eating much fiber in general.
The resistant starch, which acts as a sort of soluble fiber material, passes unchanged until it reaches the large intestine where it is fermented by gut bacteria and essentially used as food for them. While also beneficial for us, the fermentation process essentially produces air which can lead to bloating, flatulence, burping, nausea, abdominal cramps and general stomach upset. If severe, the stomach air can either cause or worsen an existing acid reflux condition and lead to severe heartburn. Because it also has a laxative effect, the resistant starch can trigger diarrhea as well. Also see What Is Gut Bacteria and What Does It Do?
Constipation may occur if you eat too many unripe bananas at once or in successive days because they contain tannins, more than the ripe fruit. Tannins are essentially naturally-occurring compounds with a bitter or sharp taste that make your mouth pucker or give you a dry mouth sensation. Tannins are also present in coffee, wine, tea, cinnamon and foods like quinces or sapodilla and when you eat them, it feels as if they are drawing all the moisture out of your mouth. Unripe bananas and even bananas that are not yet fully ripe (with some green around the stem, for example), contain various amounts of tannins and produce such effects as well as possibly constipation. The more you eat and the more sensitive you are to these compounds (some people aren’t), the more likely the side effects such as constipation.
Ripe and too ripe bananas side effects: Bananas that are too ripe can also be a source of side effects for some people. Adverse reactions may include: spikes in blood sugar levels (if you eat too many at once and they are ripe and particularly sweet) and gastrointestinal upset with symptoms such as stomach ache, acid reflux and heartburn, diarrhea or worsening of gastritis symptoms.
Cause: The resistant starches from the green bananas turn into sugars in the ripe fruit, resulting in an average sugar content of 12.23 g per 100 g of ripe banana. One medium-sized ripe banana weighing 114 g contains roughly 14.43 g of sugar, according to the United States Department of Agriculture, USDA. Eating more than 1 ripe ripe banana in one sitting or eating the ripe fruit with chocolate, honey, sugar-rich or high-carb foods can result in spikes in blood sugar levels. This can potentially occur despite the fact that bananas have a moderately low glycemic index of 51 to 54, meaning eating them causes a relatively slow release of glucose in the bloodstream. The side effect is however temporary and may only become a problem if you eat more than 1-2 bananas every day for a longer period of time.
As for the gastrointestinal upset, it may be caused by the fiber content of the fruit. One medium-sized ripe banana weighing 118 g contains 3.1 g of dietary fiber. One fruit or two a day can provide just too much fiber for some people, especially for those who are not used to eating much fiber at all or are particularly sensitive to it.
Side effects that may occur irrespective of ripening stage: Possible adverse reactions include gastrointestinal upset, worsening of gastritis symptoms, ulcers, irritable bowel syndrome and other gastrointestinal conditions, allergic reactions and anaphylactic shock.
Cause: The gastrointestinal upset is dependent on intake: the more bananas you eat at once, the higher the chances you experience gastrointestinal problems. Some people are more susceptible than others. Also, there are those that are more likely to be upset by the unripe fruit rather than the ripe fruit as well as those who find bananas in general bad for them, even with infrequent consumption. Having a digestive disorder like acid reflux disease, gastritis, peptic ulcer, irritable bowel syndrome and others can mean a higher sensitivity to fiber in particular and higher chances of gastrointestinal upset.
Banana allergy. Believe it or not, allergic reactions to bananas are possible, although rare. Banana allergy is caused by an immune system reaction to a type of protein called chitinase. As the fruit ripens, it also produces ethylene gas which encourages the production of the allergenic protein chitinase. Banana allergy is more likely to occur in people who are also allergic to avocado, pineapple, mango, passion fruit, kiwifruit, strawberries, figs, chestnuts, balloons or surgical gloves. Also read 8 Side Effects and Contraindications of Avocado. If you are allergic to one or more of the elements in the list, then you may have what is known as latex-fruit syndrome or allergy.
What this means is that eating bananas in any form can potentially trigger a severe allergic reaction with anaphylactic shock or dermatitis upon contact with the fruit, also called allergic contact dermatitis. If you have a severe form of allergy, it is imperative that you avoid such foods in all forms and proceed to undergo allergy tests to learn more about what foods and products you need to avoid. Anaphylactic shock (anaphylaxis) is life-threatening and produces symptoms such as runny nose, itchy ears, watery eyes, skin itching, redness, diarrhea, nausea, vomiting, tongue or throat swelling, shortness of breath, wheezing, coughing, difficulty breathing, headaches, low blood pressure and worse. Its onset ranges from a couple of minutes after contact or ingesting an allergen up to 24-48 hours (delayed anaphylactic shock). If you suspect anaphylaxis, seek medical help immediately.
Banana intolerance. If you’ve ever felt sick after eating bananas and it’s not just that you’ve eaten too many, they were too unripe or too ripe or you have an allergy proper, it is possible you may have an intolerance to the fruit. Banana intolerance occurs when the body cannot properly break down amines in the fruit. These compounds also occur in aged cheeses, aged, cured and smoked meat, alcoholic beverages, chocolate, tomatoes, avocado, sauerkraut etc. Because of the body’s inability to properly break down amines, eating bananas or other foods high in amines can lead to allergy-like reactions such as headaches, migraines, mood changes, heart palpitations, nausea, vomiting, abdominal cramps, diarrhea, constipation, eczema, stuffed or runny nose, watery eyes, sneezing, coughing, trouble breathing etc.
Conclusion. Depending on whether you’re intolerant of bananas at certain ripening stages because of their different nutritional profile, especially fiber profile, intolerant of bananas in general or allergic to the fruit altogether, you may experience different side effects after eating the fruit. For the most part, adverse reactions include gastrointestinal upset caused by either the resistant starches in the unripe fruit or the overall fiber content of the fruit, or allergic reactions which may vary in intensity and severity. It is important to check with your doctor if you suspect a banana allergy and make sure to avoid the fruit in the future in all forms. Other possible side effects include headaches and eczema.