Editor—Boyle and Langman summarised descriptive features and risk factors of colorectal cancer in their article.1 They seem, however, rather selective (or not well informed) of recent literature regarding dietary and nutritional factors in the aetiology of colorectal cancer. Boyle and Langman state that the intake of dietary fat and meat is positively related to risk of colorectal cancer. A high intake of meat is probably associated with increased risk of colorectal cancer, but the epidemiological evidence for fat and colorectal cancer is not as strong as they say. They referred in detail to the results in the nurses' health study published by Willett et al in 1990,2 a single prospective study that showed an increased risk of colon cancer associated with high intake of total or animal fat after adjustment for total calorie intake.
Epidemiological evidence should not be relied on from the result of a single study, but the total evidence must be considered. At least seven large prospective studies were reported in Europe and the United States up till 1999. None of these studies found a clear, positive association between fat and colon or colorectal cancer; reported relative risks for the highest versus lowest intake ranged from 0.5 to 1.2 with adjustment for total calorie intake. Six of these studies also addressed the relation between saturated fat and colorectal cancer and found no material association, with relative risks of 0.7-1.4 for the highest versus lowest intake. Giovannucci et al noted that the increased risk associated with animal fat intake in the American nurses disappeared when red meat intake was taken into account.3 Furthermore, in the combined analysis of 13 case-control studies, Howe et al showed no measurable positive association between either total fat intake or intake of saturated fat and colon cancer with adjustment for total calorie intake.4 While animal studies have suggested an aetiological role for high fat intake in colorectal carcinogenesis, such evidence is very hard to extrapolate to humans living freely.
Boyle and Langman also say that both vegetables and fruits may be protective against colorectal cancer. There is, however, little evidence regarding the protective effect of fruit against colorectal cancer; readers will relish a more accurate and succinct review article regarding dietary factors and colorectal cancer,5 which Boyle and Langman missed in the list of further readings.
Footnotes
Competing interests: None declared.
References
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