Colon (bowel) and rectal cancers - as other cancers - are increasing in the developed world. Peter Cleave, in his book The Saccharine Disease (available online for free) suggested that it was the refinement of carbohydrates and the addition of sugar to the diet that caused these diseases.
Harvard epidemiologist, Edward Giovannucci found that alcohol consumption is directly related to the risk of colon cancer:
"[...]substantial consumption of alcohol, when combined with inadequate intakes of folate and methionine, may increase risk of colon cancer [...]."
"[...] abnormally elevated levels of IGF-1, are at increased risk of colorectal tumors."
IGF-1 (Insulin -like Growth Factor - 1) levels are elevated when insulin is elevated in our bloodstream. Insulin is elevated as a result of a diet high in refined carbohydrates and sugar.
"Dr Choo Su Pin, Senior Consultant at the Department of Medical Oncology, National Cancer Centre Singapore (NCCS), observes: 'Every year, 1,500 Singaporeans are diagnosed with this form of cancer which affects men and women alike.' "
They also mention that being overweight is associated with a higher risk of developing this type of cancer. This means, that whatever factor inducing weight-loss, is also a protective factor against colorectal cancer.
Here, of course the dietary advice varies according to what we believe to be the theory in inducing weight loss. I already wrote extensively about the effects of elevated levels of the hormone insulin on weight gain. Sugar and high carbohydrates in the diet elevates insulin levels, thus contributing to the risk of obesity and - according to the studies mentioned above - of developing colorectal cancer.