CaPPtain's Blog: John Burn, October 2022
posted on Thursday, 27th October 2022
Not tagged.
CaPPtains Blog - CAPP2 Resistant Starch Update
A diet supplement of resistant starch doesn't reduce colorectal
cancers in Lynch syndrome but does reduce other types of Lynch
syndrome cancer by more than half. This is the important
result from "the other half" of CAPP2, our international research
trial which began more than 20 years ago. It appeared in the
highly regarded research journal, Cancer Prevention Research in
September 2022. It has taken a long time to reach publication
because the result is surprising.
Our CAPP2 trial was double blind, which means no-one knew
whether they were taking the resistant starch or ordinary corn
starch. They mixed 2 sachets with their food each day for
between 2 and 4 years. Some people weren't able to complete
the study, but the effect was so big that the difference was clear
even if the "early dropouts" were included. This is called an
"intention to treat" analysis. The biggest effect was on cancers in
the upper gastrointestinal tract near the stomach and including
cancers in the pipes that let bile out of the liver.
Resistant starch is turned into short chain fatty acids by
bacteria in the gut. The most important of these short chain
fatty acids is butyrate which has been known for a long time to
help reduce cancer. In addition, we think the supplement of
resistant starch may have caused a long-term change in the types of
bacteria in the gut and reduced the production of chemicals called
secondary bile acids which are released in the bile and can cause
genetic damage.
Whatever the reason, the effect on cancer risk is real and it
lasts a long time. There are no important side effects so we
think that everyone with Lynch syndrome should try to increase the
amount of resistant starch in their diet.
The name resistant starch comes from the fact that some starch
is not broken down to glucose in the upper gut. This can be
because they are inside seeds, for example, or because their
chemical structure prevents the digestive enzymes from
working. The best known example is in bananas where the
starch is crystalline but gradually breaks down to glucose as the
banana ripens; hence our advice to eat a green tipped banana a
day. There are lots of other ways to increase resistant
starch. The simple answer is to aim for a "high fibre"
diet.
The important type is resistant starch, also called fermentable
fibre in America because it reaches the bowel bacteria to be broken
down by fermentation. When starches are heated they become
easier to break down in the upper gut. I once suggested that
yesterday's pizza or cold mashed potato would work too which caused
quite a social media flurry!
The take home message is that a high fibre diet is good for you,
reduces cancer risk and can help control your weight because
resistant starch has fewer useful calories. It takes us
nearer to the wild diet eaten by our ancestors.
Speaking of ancestors, the whole CAPP story began when Professor
John Mathers invited me over 30 years ago to speak at a Newcastle
University nutrition seminar where the late great Dennis Burkitt,
who first showed that fibre is good for you, was in the audience. I
think he would approve.
John Burn
October 2022