Diet and cancer of the colon and rectum: a case-control study.

In 1979-81, 419 patients with incident cases of colon and rectal cancer and 732 controls were questioned regarding diet and alcohol. Cancer cases were a population-based series reported to the South Australian Central Cancer Registry, were 30-74 years of age, and were residing in Metropolitan Adelaide. Controls were selected from the electoral roll and individually age- and sex-matched to cancer cases. The most consistent risk factor for colorectal cancer was dietary protein, which was associated with a twofold-to-threefold relative risk for colon cancer and for rectal cancer in women for all levels of consumption above the base line (i.e., the lowest consumption quintile). For male colon cancer the corresponding relative risk was similar; but for male rectal cancer, risk was elevated only at old ages. Total energy intake and, less clearly, meal frequency were also positively associated with increased risk. Total alcohol intake (but not specifically beer) was associated with increased risk of both colon and rectal cancer in women; in both sexes, there was an increased risk of colon and rectal cancer associated with spirits consumption. A reduced risk of rectal cancer was associated with vitamin C but not with vitamin A. The increased risk associated with high protein and total energy was confined to those consuming a low fiber diet, particularly among women; but some other aspects of the relationship between fiber consumption and risk of colorectal cancer were more complex. Some modifications and extensions of the current fat-to-bile acid-to-fiber theory of bowel carcinogenesis were suggested.