Plant foods such as fruits, vegetables, grains and cereals are an important part of the diet. They provide many essential vitamins, minerals and phytochemicals (or phytonutrients) to the body, which in turn protect against various chronic diseases.

There seems no doubt that a higher consumption of vegetables in particular, is associated with less illness, especially cancer. However, while fruit and vegetables have traditionally been available to humans throughout evolution, grain foods in any quantity, have only been around since the agricultural revolution - about 10,000 years.

Recent data suggests that we may be eating too many cereals, especially refined cereals (where the bran and wheatgerm has been removed e.g. white flour). Refined cereals are not as nutritionally desirable because they have significantly lower concentrations of vitamins, minerals, phytochemicals and a higher glycaemic index (GI). Sometimes refined cereals are fortified with vitamins and minerals, but it would be difficult to add back the cocktail of phytochemicals lost during refinement.

What's good about WHOLE grains?

An increased intake of wholegrain cereals has been found to be negatively associated with heart attacks and other heart problems in 75,000 nurses over 6 years (Liu et al., 1999). An increased intake of cereal fibre has also been reported to lower the risk of coronary heart disease (JAMA 1996; 27 Supp: 447) and the inclusion of 3g per day of soluble fibre from oats results in an approximate 2% lowering of blood cholesterol levels.

There has been much media attention to the antioxidant phytochemicals in fruits and vegetables, but more recently, unrefined (wholegrain) cereals have been found to contain a whole host of phytochemicals such as tocotrienols, lignans, sterols, oryzanol, phytic acid, tannins, saponins and phenolics. These compounds found in whole grains are now thought to play a role in protecting against heart disease and cancer.

Lignans found in wholegrain cereals are converted to mammalian lignans when consumed by humans. These have a similar structure to the human hormone oestrogen and may have anti-oestrogenic effects. Higher serum lignan levels have been associated with a lower incidence of coronary events (Lancet 1999; 354 (9196): 2112). Studies by Professor Lilian Thompson at The University of Toronto, show that feeding lignans to animals which already had cancerous tumours, results in the regression of cancer and also slows cancer growth. Phytic acid has been shown to lower the glycemic index of foods, which benefits diabetics, and has also been shown to reduce the ability of iron to contribute to the development of cancerous cells in the colon. It may also have protective actions through binding iron and preventing its action as an oxidant. In relation to concerns about the action of phytic acid on mineral binding, this is not a problem with fibre intakes between 25-30g per day. Saponins, phytosterols, squalene, oryzanol and tocotrienols have been shown to have hypocholesterolaemic effects. The phenolic compounds caffeic, gallic, ellagic and coumaric acids may also have antioxidant effects.

Could we be getting too much grain food?

New research has emerged however, indicating that eating too much grain can have detrimental effects on health. The Seven Countries Study has followed the eating patterns of over 12,000 men for almost 30 years. This study has shown a decreased risk of stomach cancer and is associated with a high fruit and vegetable intake. Re-analysis of this data has shown that the risk of stomach cancer increases with high intakes of grain foods.

Risk has shown to be reduced where whole grains are consumed, but higher with high intakes of refined grains and breads. The risk remains even when the effects of cigarette smoking are taken into account. The increased risk is not only associated with high grain intakes, but other characteristics of the diet as well. High grain intakes are associated with low intakes of fruit and vegetables, so people with a high intake of grains may have other dietary characteristics, which increase their risk. In the Male Health Professional Study and the Nurses Health Study, total carbohydrate intake has not been related to a reduction
in the risk of diabetes whereas a higher cereal fibre intake was related to a lower risk. In contrast, a higher intake of high glycaemic index foods has been associated with an increased risk of developing diabetes (Diabetes Care 1997; 20 (4): 545; JAMA 1997; 277 (6): 472).

Food Guides and Cereal Intake.

Most Healthy Eating Food Pyramids around the world (e.g. American, 12345+ Food Pyramid) recommend 5 to 6 tiers of intake of the various food groups; breads and cereals are usually placed in the bottom tier of the pyramid (i.e. eat most), followed by fruits and vegetables, then dairy, then meat and finally the eat least category includes fats and sugars.

The Mediterranean and Asian Diet Pyramids place fats lower down in the pyramid. The Australian Guide to Healthy Eating, which is in the shape of a plate, recommends a larger segment of cereal foods (up to about 7 serves of cereal/day which is equivalent to 14 slices of bread), followed by vegetables/legumes and then fruit. Even though all these guides recommend a preference for wholegrain cereals, the recommended number of serves may be achieved with refined cereal products by some consumers.

Interestingly, the Australian Nutrition Foundation's (now known as Nutrition Australia) Healthy Eating Pyramid, first developed in the 1980s, has always had only 3 tiers. The 'Eat Most' tier includes Vegetables, Fruits, Legumes and Cereals, followed by the 'Eat Moderately' tier of animal foods and at the top or 'Eat Least' are the fats and sugars. In other words, a variety of plant foods are recommended in large quantities as opposed to recommending a preference for cereals over other plant foods. This may still be the soundest nutritional advice with respect to cereals.

Read about the article on nutritional profile and health benefits of cereals

References

• Cordain L. Cereal grains: Humanity's double-edged sword. In Simopoulos AP (Ed). Evolutionary aspects of Health and Diet, Exercise, Genetics and Chronic Disease. World Review of Nutrition and Dietetics, Basel, Karger, 1999;84:19-73.
• Liu S et al. Whole-grain consumption and risk of coronary heart disease: results from the Nurses' Health Study. Am J Clin Nutr, 1999;70(3):412-419.
• Margje CJF and others. Consumption of plant foods and stomach cancer mortality in the seven countries study. Is grain consumption a risk factor? Nutrition and Cancer, 1999; 34(1):49-55.
• Natoli S. Conference report - Cereals as functional foods. Dieticians Association of Australia Newsletter, March, 2000.
• To read about the scientific evidence relating cereals to disease see:
  http://www.curtin.edu.au/curtin/dept/health/dgoa/cereals.htm

Last Updated: September 2005