A starch found in bananas can reduce some cancers by more than half, according to a 20-year trial.
The international study, which included researchers from the University of Leeds, has shown a major preventive effect from resistant starch among people with high hereditary risk of cancer. Resistant starch is found in a wide range of foods including oats, breakfast cereal, pasta, rice, peas, beans and slightly green bananas.
Involving almost 1,000 patients with Lynch syndrome from around the world, the study – known as CAPP2 - revealed that a regular dose of resistant starch, 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.
This effect was particularly pronounced for upper gastrointestinal (GI) cancers including oesophageal, gastric, biliary tract, pancreatic and duodenal cancers, and was seen to last for 10 years after patients stopped taking the supplement.
The study, led by experts at Leeds and Newcastle University, is published today in Cancer Prevention Research. It is 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.
Previous research published as part of the same trial, revealed that aspirin reduced the risk of cancer of the large bowel by 50%.
Professor 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.”
Effect on bile acids
Resistant starch ferments in the large intestine, feeding beneficial gut bacteria, whereas other carbohydrates are digested in the small intestine.
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.”
Professor Tim Bishop, 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.”
Long term study
Between 1999 and 2005, nearly 1,000 participants began either taking resistant starch in a powder form every day for two years, 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 in cancer incidence between those who had taken resistant starch and those who had not. However, the research team anticipated any protective effect would take longer to develop and had designed the study for further follow-up.
In the period of follow-up, there were just five 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.
Professor Sir John Burn, from Newcastle University and Newcastle Hospitals NHS Foundation Trust who co-ran the trial, 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.”
The team is 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 research is funded by Cancer Research UK, the European Commission, Medical Research Council and the National Institute for Health Research.
“Cancer Prevention with Resistant Starch in Lynch syndrome patients in the CAPP2 Randomised Placebo Controlled Trial: planned 10 year follow-up” in published in Cancer Prevention Research 26 July 2022. DOI:10.1158/1940-6207.CAPR-22-0044.
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