Resistant starches are found in many foods, such as potatoes that have been boiled and then cooled. A new study from Great Britain now proves its positive effect on the intestines. Dietary fiber can reduce the risk of cancer by up to 60 percent if taken regularly.
What do green bananas, oats, grains, pasta, rice, peas and beans have in common? They are rich in resistant starch. This is a specific form of carbohydrate that is not digested in the small intestine but fermented in the large intestine.
A new study conducted by scientists from the universities of Newcastle and Leeds over the past 20 years shows that precisely these types of carbohydrates have a beneficial effect on the gut flora – and even the risk of cancer in the upper part of the gut by up to 60 percent can decrease.
Cancers in this region of the gut are known to be difficult to diagnose. “We found that resistant starch reduced a range of cancers by more than 60 percent. The effect was most evident in the upper part of the gut,” confirms John Mathers, Professor of Nutrition at Newcastle University.
Resistant starch comes from foods that generally contain starch – for example freshly cooked potatoes, pasta, rice or wholemeal bread. When these are consumed, the enzymatic splitting of the complex carbohydrate begins in the mouth until it is finally absorbed into the blood in the intestines as glucose.
The blood sugar level rises, insulin is released and the simple sugar glucose is transported into the cells. Scientific studies show that resistant starch – the starch from boiled and then thoroughly cooled potatoes, rice, pasta and wholemeal bread – cannot be broken down by the digestive enzymes. It is metabolized by the bacteria in the large intestine. In the colon, resistant starch promotes the growth of beneficial gut bacteria.
As part of the study, almost 1,000 patients were given resistant starch in the form of dietary supplements over a period of two years. The amount of resistant starch roughly corresponded to that contained in a slightly unripe green banana.
“The dose used in the study is equivalent to eating a banana every day: before it gets too ripe and soft, the starch in bananas resists breakdown and reaches the gut, where it can change the type of bacteria that live there,” explains Mathers.
The participants suffer from Lynch syndrome – a hereditary disease that increases the risk of cancer, especially in the colon and rectum. According to study results, the strength did not lower this hereditary risk. However, it reduced the incidence of cancer in other parts of the body by more than half.
In particular, the risk of cancer of the upper gastrointestinal tract, including oesophagus, stomach, bile duct, pancreas and duodenum, has been shown to be reduced. According to the authors, the effect of taking the dietary supplement was still observed ten years after stopping it.
Study participants took either resistant starch powder or a placebo daily for a two-year period from 1999 to 2005. In the post-observation period, five new cases of upper digestive tract cancer occurred in the 463 participants who had taken resistant starch. In the group taking a placebo, 21 out of 455 participants were affected.
The authors of the study assume that the resistant starch reduces the amount of bile acid in the intestine. However, this needs to be investigated in more detail in further studies. An excess of bile acid can damage DNA and thus promote cancer.
Resistant starch can be taken in powder form as a dietary supplement, but is naturally present in many foods. These include:
