Unripe bananas have a hereditary cancer prevention property — study

A balanced diet high in dietary fiber can do wonders for your health. Numerous studies show that increasing fiber intake improves everything from bowel movements to heart health.

Science shows that those who eat a balanced diet that’s high in fiber have a lower risk for chronic diseases later in life. But for the first time, there’s evidence that one particular diet can prevent hereditary cancer, thanks to a 10-year follow-up on an international trial.

A recent paper published in the journal Cancer Prevention Research presents a decade-long follow-up on an international trial called CAPP2. The researchers from the Universities of Newcastle and Leeds examined the effects of two interventions in those with an inherited syndrome that makes them prone to some cancers, and the findings show promise.

Science in action — This paper builds on 30 years of research, beginning with a worldwide study of nearly 1,000 people with the disease Lynch syndrome. In this illness, a person inherits a defective copy of a gene that encodes for proteins that repair our DNA. As a result, those with Lynch syndrome accumulate DNA damage throughout the body. DNA damage is a fundamental cause of cancer, so those with Lynch are more susceptible to some particular cancers, including colorectal, uterine, stomach, ovarian, pancreatic, and prostate.

In 2020, a paper published in the journal The Lancet demonstrated that taking 600 milligrams of household aspirin daily over 10 years was associated with a significantly lower risk of colorectal cancer in those with Lynch syndrome. This recent paper looks at adding another treatment in addition to aspirin: resistant starch.

Resistant starch is a type of dietary fiber found naturally in legumes, potatoes, oats, rice, and slightly under-ripe bananas.

Resistant starch is a type of dietary fiber found naturally in legumes, potatoes, oats, rice, and slightly under-ripe bananas. For this paper, participants were split into four groups and each group received one of the following treatments: starch and aspirin, starch and a placebo, a placebo and aspirin, or two placebos. This way, the researchers could see both starch’s and aspirin’s effects separately as well as compounded. Participants took their interventions for an average of two years.

“When we designed the study, we hoped to see an effect on bowel cancer,” John Mathers, director of Human Nutrition Research Centre at Newcastle University and the paper’s first author, tells Inverse. “But there was absolutely no effect in bowel cancer. The numbers of bowel cancers were almost identical in the two groups.”

Instead, they found that in groups who took resistant starch, the incidence of other types of cancer — mostly those in the upper gastrointestinal tract, such as stomach cancer — was reduced by about 50 percent. This effect persisted even 10 years after participating in the trial.

“We [had] no idea that was going to happen,” Mathers says.

Why it’s a hack — The team had good reason to look at resistant starch in the first place, but their hypothesis wasn’t quite right.

“There was quite a bit of evidence that resistant starch had biological effects that we thought would be protective against cancer,” Mathers says. His team initially thought these benefits came from the possibility that resistant starch produced a molecule called butyrate in large amounts.

“Butyrate is a little short, fatty acid, only four carbon [atoms] long, that has anti-cancer properties,” he says. Resistant starch travels through the GI tract to feed the bacteria in the gut microbiome, where a universe of organisms live and keep the gut healthy. His team’s main hypothesis was that bacteria feeding on surplus resistant starch would create a boom in butyrate production, reducing bowel cancer.

However, they hadn’t anticipated that resistant starch would change the way the body metabolizes bile acids, which are produced in the liver and roil around in the gut to help digest fat. Bile acids eventually end up in the large bowel, where the gut microbiome further metabolizes them and creates a secondary, more refined bile acid. Some secondary bile acids, Mathers says, damage DNA.

“Our working hypothesis now is that it was the alteration in bile acid metabolism that led to the lower risk of these upper GI cancers,” he says.

But wait — secondary bile is produced in the large bowel, so how could it reduce cancer further up in the GI tract?

“The reason for that is that these bile acids are recirculated via the bloodstream, back to the liver, and then recycled out into the gut,” he explains. “So these tissues in the upper intestine are exposed to those bile acids coming out of the liver. And so we think that that cluster of tissues now is exposed to less of these secondary bile acids, which is the reason why we’re seeing the lower cancer risk.”

In altering how the body metabolizes bile acid, resistant starch prevents the large bowel from producing more secondary bile acid. That leads to less DNA damage in the upper intestine, so those with Lynch syndrome won’t suffer from further unrepaired DNA.

How it affects longevity — Mathers underscores that these results are meaningful for anyone at risk for hereditary cancers, not just those with Lynch. While colorectal cancer, he says, isn’t a problem for those with Lynch because it’s so common, the secondary cancers can be harder to detect.

“These other cancers are a problem because there are no good ways of screening for them,” he says. “Very often, they’re not diagnosed until quite late, and if you’re diagnosed with cancer late, the outcomes are usually poor.”

Additionally, CAPP2 already shows that aspirin effectively reduces colorectal cancer by about 50 percent. “We already have an agent which is helpful for bowel cancer, but we didn’t have anything to help with these other cancers,” he says.

Mathers notes that this study points in a promising direction, rather than heralding a conclusive answer. “What I hope is that our studies will encourage other people with big cohorts, where they can look at very large numbers of individuals, [to] look for links between dietary fiber intake and these less common cancers of the upper GI tract,” he says.

So consider eating a greenish banana, which has more resistant starch, and don’t shy away from bread, rice, pasta, or beans.

Hack score — 🍞🥖🥔🍝🍌🍚 (6/10 starchy foods)