A study has identified a starch in unripe bananas that can reduce the risk of some cancers by more than 60 percent—and scientists say it's the first trial that points to a diet supplement that may be able to prevent hereditary cancer.

The research involving people with high hereditary risk of a wide range of cancers has shown a major preventive effect from resistant starch, found in a range of foods such as oats and slightly green bananas.

The international trial—known as CAPP2—involved almost 1000 patients with Lynch syndrome from around the world. It revealed that a regular dose of resistant starch, also known as fermentable fiber, taken for an average of two years, reduced cancers anywhere except in the bowel by more than half.

This effect was particularly pronounced for upper gastrointestinal cancers including oesophageal, gastric, biliary tract, pancreatic, and duodenum cancers.

The astonishing effect was seen to last for 10 years after stopping taking the supplement, which can also be found in breakfast cereal, cooked and cooled pasta and rice, peas and beans.

"We found that resistant starch reduces a range of cancers by over 60%. The effect was most obvious in the upper part of the gut," explained Professor John Mathers, professor of Human Nutrition at Newcastle University. "This is important as cancers of the upper GI tract are difficult to diagnose and often are not caught early on."

The study, led by experts at the Universities of Newcastle and Leeds, was a planned double blind 10 year follow–up, supplemented with comprehensive national cancer registry data for up to 20 years in 369 of the participants.

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.

"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," says Mathers. "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 to reduce 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 trial, revealed that aspirin reduced cancer of the large bowel by 50%.

Professor Sir John Burn, from Newcastle University and Newcastle Hospitals who ran the trial with Mathers, says, "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."

Between 1999 and 2005, nearly 1000 participants began either taking resistant starch in a powder form every day for two years or aspirin or a placebo—a powder which looked like resistant starch but was inactive.

At the end of the treatment stage, there was no overall difference between those who had taken resistant starch or aspirin and those who had not. However, the research team anticipated a longer-term effect and designed the study for further follow-up.

In the period of follow-up, there were just 5 new cases of upper GI cancers among the 463 participants who had taken the resistant starch compared with 21 among the 455 who were on the placebo.

"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," said University of Leeds Professor Tim Bishop, who also ran the trial.

The team are now leading the international trial, CaPP3, with more than 1,800 people with Lynch syndrome enrolled to look at whether smaller, safer doses of aspirin can be used to help reduce the cancer risk.

The paper, published this week in the journal Cancer Prevention Research, was funded by Cancer Research UK, the European Commission, Medical Research Council and the National Institute for Health Research.

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