Starchy green bananas ‘prevent cancers’ in people with hereditary risk – study

A trial in people with a high hereditary risk of a range of cancers has shown a major preventative effect from resistant starch – found in foods such as oats, cereal, beans and slightly green bananas.

The international study looked at almost 1,000 patients 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.

It showed that a regular dose of resistant starch, also known as fermentable fibre, taken for an average of two years, did not affect cancers in the bowel but did reduce cancers 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.

The study was led by experts at the Universities of Newcastle and Leeds, and was published in Cancer Prevention Research.

Previous research published as part of the same long-term trial revealed that aspirin reduced the risk of cancer of the large bowel by 50%.

Between 1999 and 2005, nearly 1,000 participants began either taking resistant starch in a powder form every day for two years, or aspirin, or a placebo.

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 five new cases of upper gastrointestinal cancers among the 463 participants who had taken the resistant starch compared with 21 among the 455 who were on the placebo.

CAPP trial
The leaders of the trial Prof Tim Bishop, Sir John Burn and John Matthews (Newcastle University/PA)

John Mathers, professor of human nutrition at Newcastle University, said: “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.

“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.”

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.”

Professor Tim Bishop, at the University of Leeds, who also ran the trial 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.”