Review article: nutrition, obesity and colorectal cancer

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Abstract
Background The age‐adjusted incidence of colorectal cancer is higher in prosperous industrialized countries than elsewhere. Dietary factors may account for 75% of sporadic colorectal cancer in the west, but the mechanisms remain obscure. Aim To review evidence for the effects of overweight and obesity, physical activity and specific dietary components on colorectal neoplasia. Methods English language papers cited on MEDLINE, obtained using search terms related to colorectal cancer, physical activity and body mass and specific food components were reviewed. Results There is evidence for adverse effects of overweight and obesity and protective effects of high physical activity against colon, but not for rectal cancer. These effects may reflect metabolic stress and chronic low‐grade inflammation. There are also modest adverse effects of red and processed meat. There is evidence for protective effects of dietary fibre, but for fruits and vegetables the evidence remains weak and inconclusive. There is some evidence for protective effects of n‐3 polyunsaturated fatty acids from fish, some micronutrients and possibly phytochemicals. The effects of many dietary constituents may depend upon genetic polymorphisms affecting a variety of genes. Conclusion Further research should focus particularly on the effects of insulin‐resistance, impaired glucose tolerance and chronic low‐grade inflammation on the colonic mucosa.