A banana is botanically a berry, and the banana plant is not a tree but a giant herb: its trunk is made of tightly packed leaf stalks. The yellow Cavendish banana that fills most stores is also a clone. It has no seeds, so every plant is grown from a cutting of another one.
Green bananas are mostly starch. In an unripe banana, 80 to 90% of the carbohydrate is starch, and much of it is resistant starch, which your small intestine cannot digest. It travels on to the colon, where gut bacteria ferment it, so it works as a prebiotic: food for the bacteria already living there, not live bacteria like a probiotic. As the banana ripens, the starch turns into sugar, which is why a ripe banana is sweeter and raises blood sugar more.
Two popular claims are bigger than the evidence. One is that bananas beat sports drinks for cyclists, but the 2012 trial that tested this found them about as good as a carbohydrate drink, not better. The other is that the potassium in a banana, about 420 mg in a medium one, stops cramps, but a small trial found that bananas barely raise blood potassium after exercise.
Health benefits of bananas
The top findings from 31 studies, strongest evidence first
What the stars mean
- Strong. Several randomized trials, pooled in a meta-analysis, point the same way, or regulators (FDA or EFSA) have approved the claim.
- Moderate. Good randomized trials support it, but there are fewer of them, or their results vary.
- Limited. Small, short or single trials, or mixed results. Promising, but it needs confirmation.
Population and lab studies get no stars: they show a link or a mechanism, not proof.
How we rate evidence →- ★★★Lower blood pressure from potassiumMore potassium lowered the top number by 3.5 mm Hg in people with high blood pressure (22 trials). It tested potassium, not bananas; a medium banana has about 420 mg.
- ★★Faster recovery from diarrhea in young childrenAdding cooked green banana to usual care roughly doubled the chance of recovery at any given time across 9 trials. In Bangladesh, day-3 recovery from acute diarrhea rose from 53% to 80%.
- ★As good as a carbohydrate drink for cyclistsOn 75 km rides, bananas matched a carbohydrate drink for 14 cyclists; separately, 20 male athletes on bananas finished 5.0% faster than on water. Dole Foods funded the university behind the first study, and authors of both studies work at its nutrition lab.
- ★Under-ripe bananas raised blood sugar lessIn people with type 2 diabetes, an under-ripe banana scored 43 on the glycemic index and an over-ripe one 74. The index rates how fast a food raises blood sugar; both bananas raised it less than white bread.
- ★Fewer hard stools in children with constipationIn 80 children and adolescents with chronic constipation, green banana biomass alone reduced hard stools, straining and pain. It did not raise the number of bowel movements per week.
All 31 studies, strongest evidence first
Getting more potassium lowered systolic blood pressure by 3.5 mm Hg, an effect seen in people with high blood pressure
Meta-analysis of 22 randomized trials (1,606 people) plus 11 cohort studies. Diastolic pressure fell 2.0 mm Hg, and in the cohort studies higher potassium intake went with a 24% lower risk of stroke. It studied potassium itself, not bananas, and the authors say the benefit applies to people whose kidneys handle potassium normally. A medium banana has about 420 mg.
Green banana added to usual care roughly doubled the rate of recovery from diarrhea in young children
Meta-analysis of 9 randomized trials (3,996 children aged 8 to 34 months) that added cooked green banana foods to standard treatment. The hazard ratio for recovery was 1.96, which means about twice the chance of recovering at any given time; it was 2.34 for persistent diarrhea and 1.74 for acute diarrhea. Seven of the nine trials were open, not blinded, and results differed moderately between trials.
Adding cooked green banana to home meals raised day-3 recovery from acute diarrhea from 53% to 80% in children
Cluster randomized trial in rural Bangladesh with 2,968 children aged 6 to 36 months. Villages, not individual children, were assigned to usual care or usual care plus cooked green banana. With prolonged diarrhea, 79.8% recovered by day 10 against 51.9% on usual care.
Green banana biomass for 24 weeks lowered HbA1c, but so did diet alone in people with prediabetes or type 2 diabetes
Randomized trial in 113 adults: 62 added 40 g a day of green banana biomass (about 4.5 g of resistant starch) to nutritional support and 51 had the diet alone. Body weight, waist, fat mass and diastolic blood pressure also fell in the banana group, but the exploratory comparison of HbA1c and fasting glucose between the groups was not significant.
Eating 250 g of banana a day for 12 weeks slightly improved the LDL to HDL ratio in people with high cholesterol
Pilot study in 30 people with high cholesterol and 15 with type 2 diabetes, who ate 250 or 500 g of banana (roughly 2 or 4 medium bananas) at breakfast every day. The LDL to HDL ratio fell from 2.7 to 2.4 and from 2.8 to 2.5 on the two amounts, and fasting glucose fell too. In the diabetes group glucose and lipids did not change significantly. The authors call the benefit marginal.
On a 75 km bike ride, eating bananas worked as well as a carbohydrate drink
Randomized crossover trial in 14 trained cyclists who ate bananas or drank a 6% carbohydrate drink, with the same carbohydrate dose, during a 75 km time trial. Finishing times (2.41 and 2.36 hours) and blood sugar did not differ, and inflammation and immune markers were similar. It found bananas equal to the drink, not better. Dole Foods funded the university, and two authors work for Dole’s nutrition lab.
Bananas and a sugar drink eased the body’s stress after a 75 km ride equally well
Randomized crossover trial in 20 cyclists who rode four 75 km time trials while taking Cavendish bananas, mini-yellow bananas, a 6% sugar drink or water only. All three carbohydrate sources lowered several inflammation markers compared with water, and bananas and the sugar drink were comparable. In a cell test with the riders’ blood plasma, COX-2 activity was lower after bananas but not after the sugar drink. Dole Foods funded the study and one author works at its lab.
Cyclists who ate bananas during a 75 km ride finished 5.0% faster than when they drank only water
Randomized crossover trial in 20 male athletes who took water, bananas or pears (0.6 g of carbohydrate per kg each hour). Pears were 3.3% faster, but that could be chance. There was no sports drink arm, so it shows that fuel helps, not that bananas beat other fuel. One author works at Dole’s nutrition lab.
In type 2 diabetes, an under-ripe banana scored 43 on the glycemic index and an over-ripe one 74
Ten people with type 2 diabetes ate 120 g of under-ripe banana, 120 g of over-ripe banana and 40 g of white bread on separate days. Both bananas raised blood sugar less than the bread did, and insulin responses were similar. The authors note that starch is 80 to 90% of the carbohydrate in under-ripe bananas and turns into sugar as they ripen.
Green banana mixed into a rice suji diet cleared persistent diarrhea in 58% of children by day 5, against 31% on rice suji alone
Open-label randomized trial in 135 children aged 6 to 35 months in Dhaka, 45 in each group. A third group on 75% rice suji also reached 58%, so the banana did no better than that diet on recovery, though it had fewer relapses (7% against 24%).
Cooked green banana in a rice diet cleared persistent diarrhea in 55% of infants by day 3, against 15% on rice alone
Double-blind randomized trial in 62 hospitalized boys aged 5 to 12 months. Pectin worked about as well as banana (59% recovered by day 3). Banana also cut stool amount, rehydration fluid and the length of the illness. It was small, all boys, and run in one country.
Two bananas a day for 60 days eased bloating but did not significantly change gut bacteria
Randomized trial in 34 healthy women with a body mass index of 24 to 30. They ate a medium banana twice a day, drank a banana-flavored drink or drank water before meals. Bifidobacteria rose in the banana group, but not by enough to rule out chance, and short-chain fatty acids did not differ. Bananas did not upset bowel habits.
Unripe banana flour shifted gut bacteria only in people whose gut was Prevotella-rich to begin with
Pilot, double-blind randomized trial in 48 healthy adults who took maltodextrin, inulin or unripe banana flour three times a week for six weeks. People with Bacteroides-rich gut bacteria showed no effect, so the same fiber may work differently from person to person. Two authors hold a patent on unripe banana flour production.
Green banana biomass alone reduced hard stools, straining and pain in children with chronic constipation
Randomized study of 80 children and adolescents split into five groups, with green banana biomass alone or with a laxative, or a laxative alone. Banana alone did not raise the number of bowel movements per week. Its main use was as an add-on: 87% of those who combined it with sodium picosulfate and 63% of those who combined it with PEG could lower their laxative dose.
Native banana starch lowered blood sugar over 48 hours compared with ordinary corn starch, in lean and obese adults
Crossover trial in which people drank 38.3 g of native banana starch or digestible corn starch twice a day for 4 days while wearing a continuous glucose monitor. Blood sugar and insulin after a test meal were lower after the banana starch, but day-to-day swings in glucose did not differ. This is a purified starch supplement, not a banana.
A drink with 40 g of banana starch reduced how much people ate at the next meal, although they did not feel less hungry
Randomized single-blind crossover trial in 28 healthy young adults who drank banana starch or digestible corn starch and then ate a test meal. Blood sugar and insulin responses were lower too, but appetite ratings and gut hormones did not change. It was a purified starch drink, and one meal only.
20 g of green banana flour a day for 45 days did not lead to weight loss in overweight women
Small study of 25 overweight women. Body composition did not change either, though hip circumference fell. In the women who met criteria for metabolic syndrome, systolic blood pressure and fasting glucose were lower.
Adding unripe banana flour to a cocoa drink gave no extra benefit for overweight women
Double-blind randomized trial in 60 women aged 20 to 50 who drank cocoa or cocoa with unripe banana flour (8.48% resistant starch) for 6 weeks. Waist size fell 2.03 cm with the banana flour drink, and body fat fell in both groups. Total cholesterol fell 19.3 mg/dL (about 0.5 mmol/L) only with cocoa alone, and the authors conclude the added fiber did not improve things further.
Unripe banana flour did not lower gut-made toxins in the blood of people on peritoneal dialysis
Double-blind, placebo-controlled crossover trial: 43 people took 21 g a day of unripe banana flour (48% resistant starch) or a placebo starch for 4 weeks each, and only 26 finished. Indoxyl sulfate dropped in the 11 people who reached the full dose, but that is a subgroup finding and the other toxins did not change.
Eating bananas after exercise in the heat raised blood potassium by only about 0.2 mmol/L after two servings
Crossover study in 9 men who cycled for 60 minutes in 36°C heat and then ate 0, 150 or 300 g of banana. Potassium stayed within normal values and rose too slowly to treat a cramp. None of the men had cramps, so it cannot say whether bananas prevent them.
A banana at bedtime improved sleep quality scores in people with insomnia, but only milk lengthened measured sleep
Study of 21 people with primary insomnia in three groups: a banana at bedtime, 200 mL of whole milk, or no change. Sleep quality scores improved in the banana and milk groups, but only the milk group showed a significant gain in total sleep time on a sleep lab recording. The groups were very small.
30 g of raw green banana flour a day sent more energy through the small intestine undigested than cooked flour
Study in 10 people with an ileostomy, which lets researchers collect what leaves the small intestine. They ate a controlled diet with raw or cooked green banana flour in random order. Raw flour also carried a little more iron out, and its leftovers produced acetate and butyrate when fermented in the lab. Banana flour did not interfere with absorption of other nutrients.
People with high blood pressure who ate bananas 3 to 6 times a week had a 24% lower risk of dying over 10 years than less frequent eaters
US survey data (NHANES 2003 to 2006) on 2,480 adults with hypertension, 658 of whom died during the follow-up. Apples 3 to 6 times a week showed a 40% lower risk, and eating both fruits 43%. Pears, pineapples and grapes showed no link. Food questionnaires are imperfect, and fruit eaters may differ in other habits.
People with abnormal blood fats who ate bananas 3 to 4 times a week had a 29% lower risk of dying over 10 years
Cohort of 2,184 patients with dyslipidemia. Apples 3 to 4 times a week showed a 39% lower risk, and eating both fruits 45%, though the range for the combination only just excluded no effect (0.30 to 0.99). Other fruits showed no such link, and a link is not proof of cause.
Each extra weekly serving of bananas was linked to a 6% lower risk of type 2 diabetes, but total fruit intake was not
Korean cohort of adults aged 40 to 69, with 2,549 cases of type 2 diabetes over 283,034 person-years. The hazard ratio of 0.94 had a range of 0.88 to 1.00, so the link is weak. Grapes showed a stronger link (0.90), while total fruit intake showed none.
Children who ate bananas every day were less likely to have wheezed than children who ate them less than once a month
Survey of 2,640 children aged 5 to 10 in Greenwich, South London. Daily banana eaters had about a third lower odds of current wheeze (odds ratio 0.66, range 0.44 to 1.00, which only just excludes no effect) and of ever wheezing (0.69). One survey at one moment cannot show cause.
Higher banana intake was linked to lower colorectal cancer risk in a large European study, but the link was not confirmed in a second cohort
Diet-wide analysis of 92 foods and nutrients in 386,792 people, 5,069 of whom developed colorectal cancer. Banana was one of 20 inverse or positive links; 13 held up in a Dutch cohort, and banana was not among them.
Green banana flour cut weight gain by 21% in mice on a high-fat diet
Study in mice, not people. After 10 weeks on a high-fat diet, mice got 15% green banana flour in their feed for 4 weeks. Fat pads were smaller and leptin, IL-6 and TNF-alpha were lower, and Firmicutes bacteria fell 23% while Bacteroidetes rose 29%.
Green banana flour helped the gut lining of mice recover faster after antibiotics
Study in mice, not people. Two weeks of antibiotics were followed by two weeks of green banana flour (400 mg per kg of body weight) or natural recovery. The flour restored the gut barrier faster by raising mucin secretion, and it enriched groups of bacteria linked to a healthy gut.
As banana flour ripened, starch and resistant starch dropped sharply while antioxidant activity rose
Lab analysis of banana flour made at the first four ripening stages. The big shift came between the second and third stages, which the authors link to the ripening peak, when phenolic compounds also increased. Other lab work does not agree on antioxidants, as the next study shows.
In Saba bananas, antioxidant activity was highest in mature green fruit and slipped slightly as ripening went on
Lab tests on five maturity stages of Saba bananas, a variety grown in Southeast Asia, with several antioxidant assays and a simulated digestion. Together with the flour study above, it shows that the idea of antioxidants rising with ripeness is not consistent across varieties and methods.
Who should be careful with bananas
Most people can eat bananas freely. Take a little care if one of these applies:
- Kidney disease, or medicine that raises potassium (ACE inhibitors, ARBs, spironolactone). Ask your doctor how many bananas fit.
- Latex allergy. Around a third of people with it react to some fruits, banana most often.
- Irritable bowel syndrome. Ripe bananas are high in FODMAPs; firm, less ripe ones are low.
How to choose, store and eat bananas
- Green: starchy and not sweet, with a glycemic index of 43. Best cooked.
- Yellow: the everyday eating banana.
- Spotted or brown: the sweetest, with a glycemic index of 74. Great for baking and smoothies.
Ripen bananas at room temperature, put them in the fridge once ripe (the peel darkens, the inside stays fine), or freeze peeled slices. Residues are no reason to skip them: in USDA tests of 703 peeled bananas, none were over the legal limit.
Sources
- Potassium in your CKD diet. National Kidney Foundation.
- Gromek W, Kołdej N, Świtała S, et al. Revisiting latex-fruit syndrome after 30 years of research. J Clin Med. 2024.
- Bananas and FODMAPs. Monash University FODMAP blog. 2017.
- Hermansen K, Rasmussen O, Gregersen S, Larsen S. Influence of ripeness of banana on the blood glucose and insulin response in type 2 diabetic subjects. Diabet Med. 1992.
- Prolonging the life of bananas. University of Nebraska–Lincoln Extension.
- Pesticide Data Program annual summary, calendar year 2020. USDA Agricultural Marketing Service. 2022.
History of bananas
Bananas were first grown in New Guinea. Archaeologists digging at Kuk Swamp in the highlands of Papua New Guinea found that bananas were being intensively cultivated at least 6,950 to 6,440 years ago. The first domesticated bananas came from wild plants that happened to grow fruit without seeds, which farmers kept and spread.
From there the banana travelled with people. Work on archaeology and language traces its path from New Guinea across Southeast Asia and all the way to West Africa. It probably reached Africa with the settlers of Madagascar around 600 AD, although earlier arrivals on the East African coast cannot be ruled out. Bananas appear in Islamic texts from the 9th century and in Palestine and Egypt by the 10th, and then spread through North Africa and Al-Andalus.
Portuguese sailors brought bananas from West Africa to South America in the 16th century. The English word “banana” is thought to come from West Africa too, possibly from the Wolof word banaana, and to have reached English through Spanish or Portuguese.
Until the 1950s the banana in a shop was not the one you buy now. It was the Gros Michel, which reached a botanical garden in Martinique from Southeast Asia and was taken on to Jamaica in 1835. Its thick peel resisted bruising and its dense bunches were easy to ship. But like all bananas it was grown from cuttings, and Panama disease, a fungus in the soil, destroyed vast plantations in Central America. By the 1960s exporters had switched to the Cavendish, which resisted the disease.
The Cavendish is named after William Cavendish, the 6th Duke of Devonshire. Around 1834 plants from Mauritius reached him, and his head gardener, Joseph Paxton, grew them in the greenhouses at Chatsworth House. The fruit trade also gave us the phrase “banana republic”. The American writer O. Henry used it in 1904 in Cabbages and Kings, a book of linked stories set in an invented country drawn from his time in Honduras, where the economy leaned on banana exports.
Now the Cavendish faces the danger that ended the Gros Michel. A Cavendish-killing variant of Panama disease called tropical race 4 has spread dramatically through the Eastern Hemisphere. Growers can mostly only try to keep it out of clean fields, and in August 2019 Colombia declared a national emergency when it was confirmed there, the first case in Latin America.
Sources
- Banana. Wikipedia.
- Denham TP, Haberle SG, Lentfer C, et al. Origins of agriculture at Kuk Swamp in the highlands of New Guinea. Science. 2003.
- Perrier X, De Langhe E, Donohue M, et al. Multidisciplinary perspectives on banana (Musa spp.) domestication. Proc Natl Acad Sci U S A. 2011.
- Gros Michel banana. Wikipedia.
- Cavendish banana. Wikipedia.
- Ploetz RC. Fusarium wilt of banana. Phytopathology. 2015.
- Banana republic. Wikipedia.
- Alarm as devastating banana fungus reaches the Americas. Scientific American. August 2019.
- Bananas, raw. USDA FoodData Central.
Frequently asked questions about bananas
Are bananas good for you?
For most people, yes. A medium banana gives you about 3 g of fiber and about 420 mg of potassium. The best-supported benefit is that cooked green banana speeds recovery from diarrhea in young children, and most other findings here come from small or short studies.
How many bananas a day is okay?
No study here sets an ideal number. In a small pilot, people with high cholesterol ate 250 or 500 g of banana a day (roughly 2 or 4 medium bananas) for 12 weeks, and the authors called it harmless. Eating one a day is common and nothing here points to harm in healthy people. If you have kidney disease or take a medicine that affects potassium, ask your doctor first.
Are bananas good for diabetics?
They can fit, and ripeness matters. In ten people with type 2 diabetes, an under-ripe banana scored 43 on the glycemic index and an over-ripe one 74, and both raised blood sugar less than white bread. In a 24-week trial, green banana biomass lowered HbA1c, but so did diet alone, so it is not a treatment. Check portions and ripeness with your care team.
Are bananas good for weight loss?
No study here shows that bananas make you lose weight. In 25 overweight women, 20 g of green banana flour a day for 45 days did not change their weight. A medium banana has about 105 calories and 3 g of fiber, so it can be a filling swap for something sweeter, but that is a swap, not a banana effect.
Do bananas help with muscle cramps?
Probably not quickly. When nine men ate one or two servings of banana after cycling in the heat, their blood potassium rose by only about 0.2 mmol/L after an hour, within the normal range and too slowly to fix an acute cramp. None of the men had cramps, so the study cannot say whether bananas prevent them.
Are green bananas healthier than ripe ones?
They are different, not simply better. Green bananas have more resistant starch, which feeds gut bacteria, and a lower glycemic index (43 against 74 in the diabetes study). The idea that ripening adds antioxidants is not consistent: one lab study found more in ripening banana flour, while another found the most in mature green Saba bananas.
Are bananas bad for your kidneys?
Not for most people, but potassium is the issue. A meta-analysis found that eating more potassium did not harm kidney function in adults, though its authors say this applies to people whose kidneys handle potassium normally. If you have kidney disease, are on dialysis or take medicine that affects potassium, ask your doctor how many bananas suit you.
Are bananas good for diarrhea?
Cooked green banana can help young children, as an add-on to usual care. A meta-analysis of 9 trials in 3,996 children found recovery about twice as fast, and in a Bangladesh village trial 80% of children with acute diarrhea had recovered by day 3 against 53% on usual care. These trials used cooked green banana, often mixed into rice-based food, not ripe yellow bananas. Children with diarrhea also need fluids, and severe cases need a doctor.