Movement for more resistant starch in your diet
Consumption of resistant starch leads to positive changes in the bowel and could protect against genetic damage implicated in bowel cancer.
26 June 2013
Glen Paul: G’day, and welcome to CSIROpod. I’m Glen Paul. In Australia bowel cancer is the second most commonly reported cancer after non-melanoma skin cancer, with more than 14,000 people diagnosed each year.
While diets typically low in fibre have been linked with a higher incidence of bowel cancer, in Australia we eat more dietary fibre than many other western countries, yet we still see 30 new cases diagnosed every day. This paradox hasn’t been lost on CSIRO Scientists, who are investigating why Australians aren’t showing a reduction in bowel cancer rates, and think the answer might lie with us not eating enough resistant starch, which is one of the major components of dietary fibre.
To find out more I’m joined by CSIRO’s Dr David Topping. David, with bowel cancer actually being one of the most preventable cancers, where are we going wrong?
Dr Topping: Well perhaps the better answer would be where aren’t we going right? A lot of this lies in history, as most of these things do. We know that fibre is good for you, and that information or that view developed as a result of work by a group of British Medical Practitioners in south and east Africa in the late ’50s early ’60s.
What happened is that the Africans seemed to consume wholemeal cereals, they eat a lot of vegetables, they also had relatively low animal protein intakes, and they didn’t get the diseases that the western people, the Europeans living in the same environment, did. And these Europeans eat a high energy, highly defined diet, and they said, “Aha, it’s the fibre.” And in those days fibre was equated with what we had called roughage, because the measures for fibre were those for foods for production animals, for farm animals, which are essentially very fibrous. Like hay, the equivalent for humans would be cereal bran.
When we look at the Australian diet, what happened is that we started to eat cereal fibres, and these cereal fibres largely from wheat are very good laxative agents, but we’ve discovered that they don’t do much else really. While they’re very important for the normal mechanical function of the bowel, and then we go back to the Africans, we find that the Africans weren’t eating that much fibre. What they were eating was a form of fibre, which we now recognise, called resistant starch, and that’s because of the way that they cooked and eat their food.
We use to do the same in western countries, but we’ve become more affluent, and so now we’ve become accustomed to hot or fresh food. What the Africans did was that they cooked their food, which gelatinised or made the starch digestible, and the eat mostly starchy foods, and then they eat it cold, and that let the starch convert itself into a form that was largely indigestible, and that’s called resistant starch, which is a contributor to dietary fibre.
Glen Paul: OK. So then how does that actually become beneficial? What’s the mechanics of it?
Dr Topping: Well the mechanics are fascinating, actually. What happens to fibre in the body is that it passes through the stomach, it goes into the mouth, down the oesophagus, into the stomach, gets pummelled around a bit, goes into the small intestine – this is food in general – there the enzymes breakdown what we can digest and absorb, proteins, fats, carbohydrate, and what’s left goes into the large bowel, it goes through a kind of way one valve and enters into the large bowel.
It spends a relatively short time in the upper gut, but it spends a long time in the lower gut, and that’s where the difference between resistant starch, which is a fibre component, and the traditional fibre components becomes apparent, because in that viscous, as we call it, that’s part of the gut, the bacteria, the resident bacteria breakdown the fibre components, just as they do in the four stomach of the sheep and cow, just as they do in the large bowel of rabbits and horses, these animals being herbivores. Well we’re omnivores, but the same process goes on.
And it’s the products of that fermentation that really make the big difference between traditional fibres and resistant starch.
Glen Paul: So why is this so important? What actually brings the bowel cancer on?
Dr Topping: We have the capacity to breakdown these traditional fibres, but the food doesn’t spend long enough there. And what’s happened with modern foods is that the processing that we have has lowered the resistant starch content to, well we think it’s virtually zero. So instead of getting their normal food supply, these bacteria – and remember that there are more bacteria in your large bowel than there are cells in your body – are effectively starving. We call it the hungry microbiome, because they’re not getting the fibre component, resistant starch, which they need. That gives them most of their energy.
So as they don’t get the energy, we don’t get the energy, because when the bacteria breakdown the fibre components, particularly resistant starch, they produce compounds called short chain fatty acids. This is just scientific jargon for very common day to day acids, acetic propionic, and butyric. You know acetic acid very well, it’s found in vinegar. Propionic acid is found in cheeses. And butyric acid is what gives parmesan cheese its smell.
And butyric acid seems to be the important acid, and what it does is it supplies energy to the skin cells, the dermal layer if you like, of the large bowel, the colonocytes, and it helps them by providing energy, and helps to maintain a normal supply, if you like, of colon cells, because they’re continuously recycling themselves, or redeveloping themselves. And what we think happens is that colon cancer is not just an exposure to toxic compounds, which does happen, but it’s due to the cells of the colon not getting their normal, if you like their normal fuel supply. And what we think is happening with colon cancer is that the colon is struggling to adapt with this restricted supply of energy.
Glen Paul: So David, what then are the best foods for resistant starch and, importantly, that these beneficial bugs are going to enjoy.
Dr Topping: Well the bugs are very beneficial, and they’ve had a very bad Press over the years, actually. Now we’re beginning to realise how important that they are for our continued good health. The foods that supply fermentable carbohydrates such as resistant starch – legumes, beans, lentils and so on.
One has to realise that resistant starch occurs for a number of reasons – it’s not just a fixed quantity, so raw starches. Bananas, green bananas especially, are a good source of resistant starch. Then there are the resistant starches that are found in whole grains, because the fibre layer in the wholegrain stops the human enzymes getting at it, so wholegrain cereals, wholegrain breads and so on. Brown rice, they’re a good source.
Then there’s the, what we call the retrograded starches. These are starches which occur when the cooked and cooled foods, and Russian salad is a prime example of that. Cooked and cooled potato retrogrades and provides quite a lot of resistant starch. The same happens actually with rice. And then there are other forms which are the chemically modified starches that you find which are usually used as food ingredients.
We can say that it’s the supply of resistant starch as a fermentable carbohydrate in modern processed foods is low, and what we’re trying to do is raise the level by tweaking the structure of the starch, by encouraging a particularly normally occurring component called amylose, which is present in relatively small amounts, and we’re increasing that in food, and that’s been done already very successfully with a commercial product called Hi-maize®. And CSIRO is helping to develop new high resistant starch cereals, we’ve got one called BARLEYmax™, and this is available in breakfast cereals and other products on supermarket shelves, and we’re doing the same for wheat.
There is also a very interesting product called Freekeh, which is eaten in the Middle East, and that is high in resistant starch, but that’s because the grain hasn’t been taken to maturity, it’s an immature or a young grain.
Glen Paul: OK. So what if I decided then just to have a diet of BARLEYmax™, or eat a lot of BARLEYmax™, is that sufficient, or does there need to be a variety?
Dr Topping: There needs to be a variety. The best dietary guideline of all is eat a variety of foods. I should emphasise though that the range of foods with the resistant starch in them is actually quite limited. There’s probably fewer than a dozen major kinds.
Glen Paul: OK. So how much then would I need to eat, or what’s the recommended intake of resistant starch on a daily basis?
Dr Topping: Not known. But the Africans seem to consume at least 25 grams per person per day. So put simply, that’s a lot of baked beans.
Glen Paul: (Chuckles). OK. And what are the other risk factors for bowel cancer that people should be aware of?
Dr Topping: Not exercising. Cigarette smoking, and that’s a risk factor for major cancers. And that probably works through restricting the supply of oxygen, because the cancer cells that grow in the bowel are what are called anaerobic, they grow in the absence of oxygen, so if there’s a restriction in the supply of oxygen, that will allow them to develop. Eating excessive amounts of certain foods, particularly processed meats – this does not mean cut out, it just means eat reasonable amounts.
Maintain your fibre intake for regularity. There is quite good evidence that the fats found in fish, the long chain polyunsaturated omega-3s are actually also protective against colorectal cancer. It’s also known that aspirin can be protective.
Glen Paul: So where can people read up on bowel cancer and your research?
Dr Topping: Well of course our research is published in scientific journals, and a lot of the work is summarised on CSIRO websites. For information about recipes, etcetera, etcetera, Bowel Cancer Australia; Australian Dieticians; the Pharmacy Guild have been terrific, they’ve got factsheets on bowel cancer; as I said the Dieticians Association; Gastroenterologists have done an awful lot of educational work in prevention. A lot of it is freely available.
Glen Paul: All right. Well, some very important research, and I thank you for sharing it with us today, David.
Dr Topping: Absolute pleasure.
Glen Paul: Dr David Topping. And to find out more about the research, or to follow us on other social media, just visit www.csiro.au.