Populations with high fibre intakes have a much lower incidence of colon cancer than similar groups with low-fibre diets. For many years it was accepted that fibre was the anti-cancer agent. This was demonstrated by adding wheat bran to the diet of people with pre-cancerous polyps in the bowel, resulting in a decrease in polyp size.
Research has indicated two ways that fibre could have anti-cancer effects:
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fatty acids produced by fermentation of fibre in the colon lower the pH, which is associated with decreased cancer risk
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fibre could bind with and remove cancer-causing agents in the colon.
However, more recent studies have cast doubt on the anti-cancer action property of fibre.
Fibrous plant foods are also rich in micronutrients and phytochemicals Some of these components could be responsible for the anti-cancer effect, or it might depend on some nutrients and active non-nutrients working together.
The cancer protection of fibrous foods is undoubted and well demonstrated, but precisely how it works has not yet been established.