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2022 October

Let's go Green Bananas - A rich source of resistant starch

14th October 2022

Luisa Carugati, BA, DipCNM 

Green bananas are generally something that most people avoid eating, waiting until they turn yellow with a few spots for maximum sweetness. But green bananas are rich in something called “resistant starch” — starches resistant to normal digestion — which carry through to the large intestine where they are a superfood for our microbiome.

For the past 20 years, the University of Leeds & Newcastle has been involved in an international study called CAPP2 looking at how resistant starch can reduce the risk of hereditary cancer. The study involved a thousand participants with Lynch Syndrome, a genetic disorder that is associated with a high risk of gastrointestinal cancers, who were put on a diet containing high amounts of resistant starch for a two-year period. The results of this study have now been released and they show a reduced risk of upper gastrointestinal cancers such as oesophageal, gastric, biliary track, pancreatic and duodenal, by an impressive half. (Incidents of bowel cancer, unfortunately, were not affected.)

Resistant starches are those starches that are resistant to digestion, and they are found in various foods, including grains, seeds, legumes and potatoes. But a particularly rich source is green (unripe) bananas. Because these starches are not digested in the small intestine, as are normal starches, they go on to ferment in the large intestine, where they provide an excellent food source for the microbiome. Professor Mathers, one of the leaders of the CAPP study, believes that the resistant starch may prevent the development of cancer by altering the bacterial metabolism of bile acids that can damage our DNA.

His colleague, Professor Tim Bishop from Leeds, cautioned that, “The results are exciting, but the magnitude of the protective effects in the upper tract was unexpected, so further research is required to replicate these finding.” In the meantime, we should keep our eyes peeled for new research, as well as our green bananas.

Please note, if you are unwell, we advise you to get a tailored treatment program from your healthcare practitioner.


“Cancer Prevention with Resistant Starch in Lynch syndrome patients in the CAPP2 Randomised Placebo Controlled Trial: planned 10 year follow-up” in published in Cancer Prevention Research 26 July 2022. DOI:10.1158/1940-6207.CAPR-22-0044.


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