Polysaccharides - The Key to a Healthy Intestine.

Chris - To human health now and the study of plant polysaccharides.  These are the giant molecules that plants make by linking sugars together to form their cell walls.  It turns out that these polysaccharides make a major contribution to keeping our intestines in tip-top shape.  Geoff Fincher.

Geoff -   We work on cereals and there's a potential to improve the value of cereals for human health.  And if we can understand how these polysaccharides are synthesized, then we can look for natural variation in the levels of their synthesis, so that we can hand on some of benefits of natural variation to human health or we can manipulate them.

Chris -   You say they're good for human health but in what way?  How are they affecting our health?

Geoff -   All right.  So as I've mentioned, cell walls over the years have been not terribly popular.  You know, student's eyes glaze over when you start talking about the structure of these polysaccharides.  But just in recent years, it's been discovered that they really have a major beneficial effect on human health in all sorts of different areas.  So, these polysaccharides have very long molecules, lots of sugar residues joined together.  They usually have an asymmetric confirmation which means they're much longer than they are wide and that means they form solutions of high viscosity.  They're thick in solution.  So you feed them to a human and there's no enzymes to digest them in the small intestine, and they increase the viscosity of the contents of the small intestine.  This slows down the rate of diffusion of enzymes and breakdown products of things that we can digest like starch and protein, and it means that there's a much slower release of say, glucose from glucose-containing polymers, a slower release generally of food.  And so, this has a lot of beneficial effects in terms of reducing glycemic index and this is of benefit to people with type 2 diabetes.  When they get down into the large intestine, down there, they're fermented to various short-chained fatty acids.  And some of these are believed to have anti-cancer effects and so, they reduce the risk of colorectal cancer.  And beyond that, there's a health claim which is allowed in the U.S. that these polysaccharides reduce serum cholesterol levels.  So if we reduce the risk of diabetes, cardiovascular disease and colorectal cancers, these things have got to be good.

Chris -   This only sounds like it, given that you've listed the things that probably kill more people than anything else.  What about the fact that we're now beginning to get very interested in the bacteria that live in our intestines as well and we know that they play a huge role in health and disease.  Do these things also impact on the bacteria as well?

Geoff -   So we, at the moment, have a project with CSIRO or Food Futures Flagship.  And this is one of the objectives, the major objectives of this project.  We have people within CSIRO who have microarray analysis where they can quantitate the level of different bacteria in our large intestine, and they can broadly classify them into good bacteria and bad bacteria in terms of human health.  And so, what we can do now is we can take these polysaccharides with different structures and we can do this either in vitro or in pigs, and we can see what effects these polysaccharides have on the dynamics of these bacterial populations.  And in our first pig trial that we finished last year, we added, we supplemented the diet with one of these cell wall polysaccharides.  We got a dramatic reduction in DNA damage in colonocytes which have lined the colon and we got a dramatic shift to beneficial bacteria in the large intestine.

Chris -   Which is very encouraging.  Are there any plants that make more of the right sort of these things?  Is that what you're trying to find, so they can then advice people what the best plants are or what would constitute the best diet?

Geoff -   Yeah.  I think that there are polysaccharides in all plants with the same sort of physico-chemical properties.  You know, they form this highly viscous solution and they have the potential to do these sort of things that I've mentioned.  But I guess the focus has been on the polysaccharides in cereals because they are the main source of food for most human societies.  And so, we're focusing on those and we certainly believe, and we can see for example, if you have different fine structures of these polysaccharides, you get different solubilities.  And the more soluble they are and the more soluble dietary fibre you have, apparently, the greater are the benefits.  So certainly, we are looking at the effect of fine structure on the physico-chemical properties and then on human health benefits.

Chris -   Do you think then in the future, if you can identify what the molecules are that are best for us, that you'll be able to put them in a pill?  Because there are some people, I think there was a stat published in the U.K. the other day, more than a million people do not eat any fruit or vegetables ever.  And I'm sure it's the same here in Australia.

Geoff -   It is the same.  It'd be a mighty big pill.  I'd have to say that because you really do need, you know, in terms of volume, you need quite a lot of this material.  But this is - but it's a good point because we have to come up with something which is beneficial to human health, which humans don't have to leave a kilogram of a day.  You know, it has to be concentrated enough in a serve of a food which is reasonable to expect people to eat.

Chris -   So can I ask you to suggest what I should have in my five-a-day on my plate, in order to get the best bang for my buck in my, not just my colon, but my intestine in total?

Geoff -   Well, I think that these polysaccharides in cereal grains, probably the best ones that are naturally occurring are in oats and barley.  Now oats, you can have so, eat up your porridge and you'll do really well in terms of bowel health.  Barley is also are rich source, but it's not quite as attractive as a human food and what we're trying to do is increase the solubility and the amount of these polysaccharides in wheat so that people can get them through wheat, and eventually rice as well.