Written by Jeanna D. Smiley — Fact checked by Hannah Flynn
Resistant starches (RS) are carbohydrates that pass undigested through the small intestine and are digested, or fermented, in the large intestine.
They are present in plant-based foods including beans, oats, breakfast cereals, rice, cooked and cooled pasta, peas, and slightly unripe bananas.
RS forms part of dietary fiber, which is known to reduce the risk of colorectal cancer and many other non-communicable diseases.
Researchers at Newcastle University and the University of Leeds in the United Kingdom found that a RS powder supplement may help prevent cancer in people with Lynch syndrome.
The experts ran a multinational trial called CAPP2 involving almost 1,000 people with Lynch syndrome. They gave the participants a 30g dose of RS for an average of two years.
The supplementation did not affect colorectal cancers as expected. However, unexpectedly, its protective potential was most apparent in the upper digestive tract, where cancers are aggressive and not usually caught early.
These findings appear in Cancer Prevention Research.
What is Lynch syndrome?
Lynch syndrome, an inherited condition, predisposes people to colon cancer, gastric cancer, and several other cancers.
Medical News Today spoke with Dr. Anton Bilchik, surgical oncologist and division chair of general surgery at Providence Saint John’s Health Center and chief of medicine at Saint John’s Cancer Institute in Santa Monica, CA.
Dr. Bilchik, who was not involved in the study, shared that LS is caused by a genetic mutation that stops the DNA from being able to correct itself after cell division as effectively as it should, which can give rise to cancers. It occurs in about 1% of patients with colorectal cancer.
The U.K.’s National Institute for Health and Care Excellence (NICE) recommends that people with LS take aspirin daily for at least two years to help prevent colorectal cancer.
Until now, prophylactic surgery to remove noncancerous organs or glands was considered the only preventive measure against LS-related cancers outside the colon.
An unripe banana a day
The CAPP2 trial analyzed the long-term effects of aspirin and RS on cancer onset in patients with Lynch syndrome.
Earlier research during the trial found that aspirin reduced colorectal cancer by 50%.
A total of 463 participants took 30 g of RS daily for up to four years, and 455 subjects took a placebo.
The dose used was equivalent to eating one slightly unripe banana daily. Bananas at this stage resist breakdown in the small intestine, reaching the large intestine and feeding the microbiome there.
The researchers planned a 10-year follow-up and investigated data from the U.K.’s National Cancer Registry over 20 years.
They found no difference in the number of colorectal cancer cases. However, fewer participants receiving the supplement developed non-colorectal LS cancers compared to those taking the placebo.
The study noted: “The reduction in non–colorectal cancer LS cancers was detectable in the first 10 years and continued in the next decade.”
Protection against some cancers
RS supplementation over an average of 25 months did not lower colorectal cancer risk in LS patients, the team found.
They reported: “Dietary supplementation with RS for this limited time period does not emulate the apparently protective effect of diets rich in [dietary fiber] against colorectal cancer in the general population.”
Surprisingly, the participants taking RS were 60% less likely to be diagnosed with non-colorectal LS cancers.
The protective effect was most evident with upper GI cancers, including stomach, bile duct, pancreatic, and duodenal cancers. The researchers found five cancers in five participants on RS compared to 21 cancers in 17 of the control group.
Currently, the researchers are leading another multinational trial involving over 1,800 individuals with Lynch syndrome. The CaPP3 study aims to determine if smaller doses of aspirin can help reduce cancer risk.
How RS may reduce cancer risk
The present study’s authors have yet to determine exactly how RS reduces upper GI cancer risk. However, they are certain that the gut microbiota plays a part.
Gastrointestinal microbes produce a short-chain fatty acid called butyrate while breaking down RS. This compound helps stop the growth of cancer cells and might induce cancer cell death.
According to Dr. Bilchik, one theory is that an increase in butyrate may contribute to reductions in upper GI cancers.
The study’s authors believe that RS’s effect on bile acids may also help explain the reduced LS cancer risk.
An unrelated 2022 Advance Science article reported that interactions between bile acids and the gut microbiome may be associated with GI cancer development.
The study’s limitations
Dr. Bilchik wondered how the U.K. researchers arrived at using 30 g of RS in the study. He said that such a figure is “very difficult for people to interpret” in real life.
The surgeon also noted that the study does not establish causality.
Overall, he found this research “very exciting, because the predominant causes of death in patients with Lynch syndrome are upper gastrointestinal cancers. So, those can be reduced [with RS], and that’s significant.”
The implications are impressive since these cancers are more challenging to diagnose and overcome than other LS cancers.
Food choices vs. supplements
Dr. Bilchik expressed concern that taking RS or probiotic supplements “may disrupt what already exists in our body to protect us against cancer.”
He appreciated the current study for supporting “a lot of evidence that high fiber diets reduce the chances of getting colorectal cancer”.
Dr. Michael Greger, a physician, author, and clinical nutritionist who was also not involved in the study, encourages the consumption of whole foods over supplements to fight and beat cancer.
In a recent NutritionFacts.org podcast, Dr. Greger stated:
“Foods contain many thousands of substances that lead to vast numbers of possible interactions, yet much of nutritional science has long been directed [toward] the impact of single dietary components.”
“Yes, this kind of ‘reductionist’ approach can reveal the role of individual nutrients or foods in the development of disease, but let’s think about what the optimal research strategy would be to study the effects of bioactive natural plant compounds on disease prevention,” he added.
This article originally appeared here and was republished with permission.