A trial that has run for more than two decades has claimed that starchy foods such as green bananas could help prevent cancers in those who have a hereditary risk.
The study looked at people with Lynch syndrome – a genetic condition which leads people to be predisposed to a range of cancers, and for which around one in 300 people are a carrier.
Analysing data from almost 1,000 patients, researchers from institutes including the Universities of Newcastle and Leeds found that the risks for certain cancers may be reduced over a long period of time by starch.
Published in Cancer Prevention Research, the study showed that a regular dose of resistant starch taken for an average of two years may reduce risks of certain cancers.
Starch, which can be found in oats, cereal, beans and slightly green bananas, did not affect cancers in the bowel but did reduce it in other parts of the body by more than half.
The effect was particularly pronounced for upper gastrointestinal cancers including oesophageal, gastric, biliary tract, pancreatic and duodenum cancers, which can be difficult to detect.
The remarkable effect was seen to last for 10 years after stopping taking the supplement and experts hope the resistant starch findings were beneficial to the general population, not just people with Lynch syndrome.
John Mathers, professor of human nutrition at Newcastle University, said: “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. This is important as cancers of the upper GI tract are difficult to diagnose and often are not caught early on.
“Resistant starch can be taken as a powder supplement and is found naturally in peas, beans, oats and other starchy foods.
"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.”
He added: “Resistant starch is a type of carbohydrate that isn’t digested in your small intestine, instead it ferments in your large intestine, feeding beneficial gut bacteria – it acts in effect, like dietary fibre in your digestive system.
“This type of starch has several health benefits and fewer calories than regular starch.
“We think that resistant starch may reduce cancer development by changing the bacterial metabolism of bile acids and reducing those types of bile acids that can damage our DNA and eventually cause cancer.
“However, this needs further research.”
Previous research published as part of the same long-term trial also revealed that aspirin reduced the risk of cancer of the large bowel by 50 percent.
Professor Sir John Burn, from Newcastle University and Newcastle Hospitals NHS Foundation Trust who ran the trial with Professor Mathers, 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.
“Patients with Lynch syndrome are high risk as they are more likely to develop cancers so finding that aspirin can reduce the risk of large bowel cancers and resistant starch other cancers by half is vitally important.
“Based on our trial, NICE now recommend aspirin for people at high genetic risk of cancer, the benefits are clear – aspirin and resistant starch work.”
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