Heartening news for graingrowers and consumers: there's mounting evidence that a diet high in unprocessed grains helps protect against various cancers and heart disease.
A round-up of recent research shows the outer layers of grains help to combat the risk of bowel and possibly breast cancer in a number of ways, according to CSIRO Health Sciences & Nutrition's Graeme Mcintosh. Dr Mcintosh presented the findings to the Royal Australian Chemical Institute Convention cereal nutrition symposium in Canberra.
He said that, unfortunately, most Australians eat less than the amount of cereal dietary fibre-rich foods considered by many scientists to be necessary to achieve protection.
"The benefits of fibre to health are established—but the picture is looking more complex, especially in understanding the processes whereby it improves gut health," he said.
Cancer fighters in the outer layer
The outer layers of grains from which brans are made, besides being the richest source of insoluble dietary fibres, also contain a wide range of substances likely to be active against cancers: phytates, lignans, flavonoids, phytosterols, vitamins E and B and certain trace elements, such as selenium.
Researchers say lowered cancer risks are probably related to these substances and how they are processed by microbes in the human digestive tract. This is how it may work:
- fermentation of dietary fibre by gut microbes leads to high levels of short chain fatty acids which are thought to reduce the risk of colon cancer
- antioxidants in the fibre help to suppress the oxygen free radicals which can cause genetic damage leading to cancer
- phytates bind up iron and other substances which can otherwise promote oxygen damage in the large bowel phytoestrogens and lignans suppress the activity of oestro-gens which may promote breast cancer.
"Researchers found that women on high grains and/or plant diets had high levels of lignans in the urine — and this correlated with a reduced breast cancer risk by a factor of about two-thirds," said Dr Mcintosh.
Dr Mcintosh said new tests are in the pipeline to assess preventive dietary strategies and provide useful measures of an individual's risk of colon or breast cancer.
He also cautioned that popular grain-based foods such as white bread, polished rice and white pasta contribute little cereal fibre. They may however provide useful intakes of resistant starch, which exhibits some of the characteristics of dietary fibre considered beneficial.
"We ought to be eating wholemeal or high-fibre breads with every meal — about four to five slices a day, besides our breakfast cereal."
The fact that whole grains also appear to protect against heart disease opens the way for a much healthier Australian diet in the future, based on the natural goodness of grains, in combination with other desirable foods.
Some of Dr Mcintosh's research has been supported by growers and the Federal Government through the GRDC.
Program 1.1.1 Contact: Dr Graeme Mcintosh 08 8303 8884
Other updates on grains in human and animal nutrition are published in the program and abstracts from the symposium. Contact Trish Griffiths, BRI Australia 02 9888 9600.