What is in it
A medium banana of about 118 g provides roughly 105 kcal, 27 g of carbohydrate, 3.1 g of fibre and 422 mg of potassium (Nieman et al., 2012). Banana flesh also contains a small amount of dopamine, about 0.42 mg per 100 g, but dopamine in the blood cannot cross into the brain (Nieman et al., 2012).
Bananas are unusually rich in polyphenol oxidase, the enzyme that turns a cut banana brown. In one analysis, banana had about 3,258 units of activity per 100 g, compared with 570 in a Red Delicious apple and 12 in highbush blueberries (Ottaviani et al., 2023). The same enzyme can break down flavanols from other foods once they are blended together.
Polyphenols at a glance
These figures come from the Phenol-Explorer database and are given in mg per 100 g of the fresh food (Neveu et al., 2010; Phenol-Explorer, n.d.). The database records how each value was measured, and the methods are not interchangeable: chromatography identifies and measures individual compounds, some values are measured after the compounds have been broken down chemically (hydrolysis), and the Folin assay gives a single figure for total phenolic content.
Show the individual compounds
All values in mg per 100 g fresh weight, from Phenol-Explorer. Compounds that were tested for but not detected are not listed.
Reading these figures. When individual compounds are measured, banana contains very little: about 1.3 mg of catechin and 1 mg of gallic acid per 100 g, and the catechin figure varies from 0 to about 10 mg between samples. The Folin assay gives a much higher total of about 154.7 mg (5 samples from 5 studies), ranging from 11.8 to 231.0 mg. The two methods measure different things, so the figures should not be compared directly.
The dopamine in banana (Nieman et al., 2012) is not included in Phenol-Explorer’s polyphenol data.
What the evidence tells us
Well supported
None of the banana findings we have read so far reaches this label.
Promising
Banana can lower how much flavanol you absorb from a smoothie. In a small crossover study in healthy men, a banana smoothie containing added cocoa flavanols produced 84% lower peak blood levels of the flavanol epicatechin than the same amount taken as a capsule, while a mixed-berry smoothie, which is low in polyphenol oxidase, did not differ from the capsule. When a flavanol drink was simply taken alongside a banana drink, absorption was 37% lower (Ottaviani et al., 2023). The study was small, included only men, and was funded by Mars, Inc., which makes cocoa flavanol products; three authors were Mars employees.
Fuel for exercise. In 14 trained cyclists, bananas supported a 75 km time trial as well as a sports drink with the same amount of carbohydrate, although riders felt fuller and more bloated after the bananas (Nieman et al., 2012). The study was funded by Dole Foods.
Plausible pathway
Green banana and gut bacteria. Green banana powder raised several Bifidobacterium species in two weeks (Chong et al., 2024), but the study was short, industry-funded, and used a processed powder rather than the fruit most of us eat.
Digestive comfort. Green banana powder is rich in resistant starch, which reaches the colon and is fermented by gut bacteria (Chong et al., 2024), so it is reasonable to ask whether it causes discomfort. In the two trials we have read, powders containing green banana were generally well tolerated. In the two-week trial, no one reported constipation or diarrhoea from 10.75 g of green banana powder a day, bloating was reported as low, and stools became softer (Chong et al., 2024). In a six-week trial of a resistant starch blend made from potato starch, green banana flour and apple fibre, most people tolerated it, but one person stopped at the highest dose, 30 g a day, because of severe bloating and constipation. Doses in that trial were built up gradually (Hanes et al., 2022). Neither trial tested whole green bananas. General advice on adding fibre gradually is on the recipes page. We have not yet checked the funding statement of the Hanes trial; the capsules used to measure gut conditions were provided by Amway.
What we do not know
The flavanol study measured only epicatechin, the main flavanol in cocoa. It did not test whether banana affects the anthocyanins in blueberries. We have not read a study comparing ripe and green banana in people, or one linking bananas to blood pressure.
References
Chong, C. W., Liew, M. S., Ooi, W., Jamil, H., Lim, A., Hooi, S. L., Tay, C. S. C., & Tan, G. (2024). Effect of green banana and pineapple fibre powder consumption on host gut microbiome. Frontiers in Nutrition, 11, Article 1437645. https://doi.org/10.3389/fnut.2024.1437645
Hanes, D., Nowinski, B., Lamb, J. J., Larson, I. A., McDonald, D., Knight, R., Song, S. J., & Patno, N. (2022). The gastrointestinal and microbiome impact of a resistant starch blend from potato, banana, and apple fibers: A randomized clinical trial using smart caps. Frontiers in Nutrition, 9, Article 987216. https://doi.org/10.3389/fnut.2022.987216
Neveu, V., Perez-Jiménez, J., Vos, F., Crespy, V., du Chaffaut, L., Mennen, L., Knox, C., Eisner, R., Cruz, J., Wishart, D., & Scalbert, A. (2010). Phenol-Explorer: An online comprehensive database on polyphenol contents in foods. Database, 2010, Article bap024. https://doi.org/10.1093/database/bap024
Nieman, D. C., Gillitt, N. D., Henson, D. A., Sha, W., Shanely, R. A., Knab, A. M., Cialdella-Kam, L., & Jin, F. (2012). Bananas as an energy source during exercise: A metabolomics approach. PLoS ONE, 7(5), Article e37479. https://doi.org/10.1371/journal.pone.0037479
Ottaviani, J. I., Ensunsa, J. L., Fong, R. Y., Kimball, J., Medici, V., Kuhnle, G. G. C., Crozier, A., Schroeter, H., & Kwik-Uribe, C. (2023). Impact of polyphenol oxidase on the bioavailability of flavan-3-ols in fruit smoothies: A controlled, single blinded, cross-over study. Food & Function, 14(18). https://doi.org/10.1039/d3fo01599h
Phenol-Explorer. (n.d.). Showing all polyphenols found in banana, raw (Version 3.6) [Data set]. Retrieved October 18, 2026, from http://phenol-explorer.eu/contents/food/159
