A banana a day may prevent cancer, but only if it’s green, a new study suggests.
Researchers found that giving people with a hereditary risk of cancer a diet rich in resistant starch more than halved their risk of developing certain types of the disease.
Resistant starch is a type of carbohydrate, a type of energy-providing food, and is commonly found in foods such as oats, whole grains, beans, and some green bananas.
An international study led by UK experts looked at almost 1,000 patients with Lynch syndrome – a genetic disorder that leaves people prone to a range of cancers.
Around 200,000 Britons are thought to have the genetic condition, but less than 5 per cent know they are carriers.
Given to study participants The average daily dose of resistant starch equivalent to one unripe banana is two years.
Although it did not reduce the risk of colon cancer, the dose reduced the risk of cancer in other parts of the body by up to 60 percent, experts said.
British experts have found that resistant starch, a type of carbohydrate in green bananas, can help reduce the risk of cancer in people with a high genetic predisposition.
What is Lynch syndrome?
Lynch syndrome is a genetic disorder that predisposes people to a number of cancers.
The condition means that a gene involved in correcting errors in DNA replication, produced when tissue is created or replaced, does not work properly.
Over time, these mistakes add up and increase the risk of developing cancer.
People with Lynch syndrome are more likely to develop colon cancer and other cancers at a younger age than most people.
Bowel Cancer Research UK says Lynch syndrome increases the risk of bowel cancer by 80 per cent.
The charity believes Lynch syndrome is responsible for more than 1,200 cases of bowel cancer in the UK each year.
Lynch syndrome affects one in 300 people, with 200,000 Britons thought to have it.
However, only 5 percent of people with the condition know they have it.
This protective effect was particularly strong for cancers of the upper gastrointestinal tract, including cancers of the esophagus, stomach, biliary tract, pancreas, and duodenum, which are difficult to detect.
The protection was seen to last for 10 years after stopping the supplements, and experts hope the results will be useful not only for people with Lynch syndrome, but also for the general population.
The study was carried out by experts from the Universities of Newcastle and Leeds and published in the journal Cancer Prevention Research.
Between 1999 and 2005, nearly 1,000 participants took either powdered resistant starch or a placebo daily for two years.
At the end of the treatment phase, there was no overall difference between those who received resistant starch and those who did not.
However, the research group planned for long-term effects and further research.
During follow-up, only five new cases of colon cancer occurred among the 463 participants who received the resistant starch, compared to 21 among the 455 who received the placebo.
Professor John Mathers, an expert in human nutrition at Newcastle, said: “We found that resistant starch reduced a number of cancers by more than 60 per cent.”
“The effect was most pronounced in the upper part of the intestines.”
“This is important because upper gastrointestinal cancers are difficult to detect and often go undiagnosed.”
He added that the dose of resistant starch used in the trial was equivalent to that in an unripe banana.
“Resistant starch powder can be taken as a supplement and occurs naturally in beans, peas, oats and other starchy foods,” he said.
“The dose used in the trial is equivalent to eating a banana a day; before they are overripe and soft, the starch in the banana can resist breakdown and reach the gut and change the type of bacteria that live there.’
Professor Mathers said the researchers suspected resistant starch, which is not digested in the small intestine but is instead fermented in the large intestine, feeding beneficial gut bacteria and altering the production of bile acids.
“We think that resistant starch may reduce the development of cancer by changing the bacterial metabolism of bile acids and reducing the types of bile acids that can damage DNA,” he said.
“However, this requires further study.”
Professor Tim Bishop, a genetics expert at Leeds who took part in the study, added that the results were interesting, but that further research was needed.
“The results are interesting, but the magnitude of the protective effect in the upper gastrointestinal tract was unexpected, so further studies are needed to replicate these findings,” he said.
Lynch syndrome is a genetic condition in which errors in DNA replication are rarely repaired.
This means that mutations can accumulate over time and lead to cancer, especially in the colon.
According to the NHS, around half of people with Lynch syndrome will develop bowel cancer.
The charity, Bowel Cancer UK, estimates that 1,200 cases of bowel cancer are caused by Lynch syndrome each year.
The condition is also responsible for around 1,000 other cancers in the UK each year.
In the United States, Lynch syndrome is estimated to cause approximately 4,200 colon cancers and 1,800 uterine cancers per year.