We generally consume ripe yellow bananas because they are sweet and fibrous. These are great for constipation and digestive health, but eating green, unripe bananas can provide unexpected benefits, including cancer prevention.
The 20-year-long study involved Lynch Syndrome patients at a greater risk of developing rectal and intestine cancer. They were asked to consume a dose of resistant starch, which can also be obtained from unripe green bananas.
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This starch is also found in rice, peas, oats, beans, and certain cereals. But bananas have the maximum amount, which is why they are the best source of this cancer-reducing starch.
The study findings were published in Cancer Prevention Research, the American Association for Cancer Research journal. Known as CAPP2, the study involved 1,000 participants with Lynch Syndrome (HNPCC). This inherited disorder increases the risk of cancer, particularly cancers of the colon (large intestine) and rectum, before age 50.
The participants received a dose of resistant starch equivalent to an amount one would receive from eating a banana that isn’t overly ripe and is still a bit green.
The study revealed that a regular dose of resistant starch, taken for an average of two years, did not affect bowel cancers but reduced cancers in other body parts by more than half, including upper gastrointestinal (GI) cancers.
The study, led by experts at the Universities of Newcastle and Leeds, could have significant implications in reducing cancers in the upper part of the gut, which doctors say can be hard to spot and diagnose.
“We found that resistant starch reduces a range of cancers by over 60 percent. The effect was most obvious in the upper part of the gut,” John Mathers, study co-author and professor of human nutrition at Newcastle University, said in a statement.
“The dose used in the trial is equivalent to eating a daily banana: before they become too ripe and soft, the starch in bananas resists breakdown and reaches the bowel where it can change the type of bacteria that live there.”
Co-author Tim Bishop, professor of genetic epidemiology at the Leeds School of Medicine, said: “The results are exciting, but the magnitude of the protective effect in the upper GI tract was unexpected, so further research is required to replicate these findings.”
Why does resistant starch protect against cancer?
Resistant starch is taken as a powder supplement and found in a wide range of foods such as oats, breakfast cereal, cooked and cooled pasta or rice, peas and beans, and slightly green bananas.
It is a type of carbohydrate that is not digested in the small intestine. Instead, it ferments in the large intestine, feeding beneficial gut bacteria. “It acts in effect, like dietary fiber in your digestive system,” Professor Mathers said.
This effect was particularly pronounced for upper gastrointestinal (GI) cancers, including oesophageal, gastric, biliary tract, pancreatic, and duodenal cancers. In addition, it was seen to last for ten years after participants stopped taking the supplement.
Professor Mathers added: “We think that resistant starch may reduce cancer development by changing the bacterial metabolism of bile acids and to reduce those types of bile acids that can damage our DNA and eventually cause cancer. However, this needs further research.”
Co-author John Burn, professor of clinical genetics at Newcastle University, said: “When we started the studies over 20 years ago, we thought that people with a genetic predisposition to colon cancer could help us to test whether we could reduce the risk of cancer with either aspirin or resistant starch.”
Previous research published as part of the same trial revealed that aspirin reduced cancer of the large bowel by 50 percent. “Based on our trial, NICE [The National Institute for Health and Care Excellence] now recommend aspirin for people at high genetic risk of cancer; the benefits are clear — aspirin and resistant starch work,” Professor Burn said.