Many of the cereals (grains) that we consume are refined. Grains are first broken into pieces and then refined, sifting away the bran, germ and, usually, the aleurone layer. This removes most of the fibre, oil, and B vitamins, as well as approximately 25 percent of the protein. Polishing, as often performed on rice, removes additional nutrients. Many high-income countries therefore fortify refined cereals, including flour, with B vitamins and iron. Wholegrain products generally contain the constituents of the grain but, given the absence of an internationally accepted definition, intact grains are present to a variable extent. The extent to which the grain remains intact influences physiological processes in the bowel and hence health.
Cereal foods may be eaten in wholegrain form, although consumption in refined forms, such as white rice, bread, or pasta, is generally much more common, particularly in high-income countries. Refined grains are considered easier than whole grains to cook and to chew; are light in color- which is attractive to many consumers; and also have a longer shelf-life than wholegrain products, as the oil in bran goes rancid relatively quickly.
Breakfast cereals, particularly in the United States and parts of Europe, also amount for a significant proportion of grain eaten. Many breakfast cereals, although based on grains (whole or refined), may contain substantial amounts of added sugars. Grains are further processed to provide ingredients such as corn syrup, starch, or alcohol. They also form the basis of many animal feeds.
Glycaemic index (GI) is a measure of the degree to which a food raises blood glucose compared with a standard food (usually glucose or white bread) under standard conditions. Processed grains have a higher GI than unprocessed grains and generally, the greater the degree of processing, the greater the GI. The degree to which different foods and meals raise blood glucose depends not only on the nature of the carbohydrate, but also on the characteristics of the foods consumed.
The relevance to cancer might lie in the fact that the rise in blood glucose after a meal is closely linked to that of insulin, which apart from its crucial role in carbohydrate and lipid metabolism, is also one of a family of important growth factors.
The direct evidence that cereals (grains) affect the risk of any cancers remains unimpressive. The evidence that foods contaminated with aflatoxins (aflatoxin B is considered the most toxic and is produced by Aspergillus flavus and A. parasiticus) are a cause of liver cancer is convincing. Cereals (grains) and peanuts are the foods most commonly infested by these fungal toxins. Contamination is most widespread in countries with hot, dump and poor storage facilities.
Recently, baby food manufactured by a North York company has been recalled because it may contain elevated levels of a toxin called Ochratoxin A (OTA) produced by aspergillus and penicillium. OTA is a mycotoxin, which is a toxin produced by a fungus. A mycotoxin may be formed when grains become mouldy. OTA has been classified by the International Agency for Research on Cancer as a possible cancer-causing substance. This present particularly in cereal and grain products, also in dried fruits, wine, coffee, beer, cocoa, juices, spices, pork, poultry and dairy products. OTA may cause damage to DNA which may increase the risk of cancer. There is some evidence that OTA can cause kidney tumors and breast tumors in rats. Scientists yet to conclude whether or not exposure to OTA causes cancer in humans-more research are needed.