Taking a regular dose of resistant starch, otherwise known as fermentable fiber, might help prevent certain types of cancer, a new trial has found.

A type of carbohydrate that doesn’t get digested in the small intestine, resistant starch is commonly linked to improved gut health since it leads to more good bacteria that help lower constipation and cholesterol levels and reduce the chance of gas pains.

It’s found in foods like oats, cooked and cooled pasta, breakfast cereal, peas, beans and slightly green bananas. It’s also commonly taken as a diet supplement for weight loss.

A successful international trial by experts from the Universities of Newcastle and Leeds has revealed that it can also reduce certain cancers in the body by more than half. The effect was more pronounced in upper gastrointestinal cancers, like gastric, biliary tract, esophageal, and duodenum cancers, when taken for an average of two years.

Published in the Cancer Prevention Research, a journal of the American Association for Cancer Research, the international trial – known as CAPP2 – is a planned double-blind 10-year follow-up that involved more than 1,000 patients suffering from Lynch syndrome. The research was also supplemented with comprehensive national cancer registry data for up to 20 years in 369 study participants.

Professor John Mathers, a professor of Human Nutrition at Newcastle University and part of the team that ran the trial, explained that resistant starch reduced a range of cancers by over 60%, noting that it’s most obvious in the gut’s upper part. This highlights the significance of the findings since cancers of the upper GI tract are often difficult to diagnose or catch in the early stages.

“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.

Previously, a research published in The Lancet as part of the trial revealed that aspirin reduced hereditary colorectal cancers by 50%.

The team is now leading the international trial, CaPP3, where they are looking at whether smaller, safer doses of aspirin would be effective for use in reducing cancer risk in people with Lynch syndrome.