Colorectal cancer (CRC) is the second most common cause of cancer deaths in Europe with 214,800 deaths (12% of all cancer related deaths) in 2012 (Ferley et al 2015). It is, however, a cancer with strong associations with lifestyle factors including smoking, alcohol consumption, obesity, processed and red meat consumption and lack of physical activity, suggesting that it is potentially preventable. The role of fruit and vegetable (F&V) consumption in CRC risk has been extensively studied. Although results for specific plant foods have been somewhat inconsistent, the 2011 review of epidemiological studies by the World Cancer Research Fund judged the evidence for decreased CRC risk with foods containing dietary fiber as ‘convincing’, and with that for fruit and non-starchy vegetables as ‘limited- suggestive’.
A study published in March this year indicates that plant food-based dietary patterns are important in modifying CRC risk. This was a conclusion of an analysis of the US Adventist Health Study – a large prospective cohort trial of over 96,000 subjects with a mean follow up of 7.3 years. The authors explored the relationship between incident cancers of the colon and rectum and 4 vegetarian patterns (vegan, lacto-ovo-vegetarian, pesco-vegetarian, semi-vegetarian) and a non-vegetarian pattern (Orlich et al 2015). The adjusted hazard ratio (HR) for all vegetarians combined vs non-vegetarians was 0.78 (95% CI, 0.64-0.95). Pesco-vegetarians showed the biggest decrease in CRC risk of 43% (HR 0.57, 95% CI 0.40-0.82) and semi-vegetarians the smallest (8% decrease which was not significant). Importantly the effects were consistent across the sexes and ethnic groups studied.
The above are all epidemiology studies, which indicate associations between diet and CRC risk but do not provide evidence of causal relationships.
A recent Alpro Foundation-funded research project (Sitthiphong et al 2015) attempted to address this issue by conducting a randomized, controlled dietary intervention trial in 82 healthy subjects. The study aimed to determine whether there was a dose response relationship between the amounts of F&V, especially those high in flavonoids, and DNA damage. The study was a parallel design with 3 study groups, participants in the two intervention groups (flavonoid-rich and flavonoid-poor F&V intake groups) were asked to increase F&V intake by 2, 4 and 6 portions for a duration of 6 weeks each, while a third group continued with their habitual, low F&V diet.
The endpoints were oxidized DNA damage in peripheral blood mononuclear cells (PBMC) and the capacity of stool samples to induce DNA damage in cultured colon cells. Although these are not validated biomarkers of cancer risk, DNA damage is a critical step in the initiation and development of cancer. Oxidized DNA damage was significantly decreased in the flavonoid-poor F&V intake group at additional doses of 4 and 6 portions/day compared to pre-intervention. Assessment of the capacity of stool samples to induce DNA damage in vitro in human intestinal cells in culture was also measured by the Comet assay. There was a dose- related decrease in DNA damage in the LF group (most apparent after an additional 6 portions /d). In the HF group there was a trend for decreased DNA damage but the effect was only significant at the highest F&V intake.
Taken together the latest studies indicate that the risk of colorectal cancer can be reduced by plant-based diets.
Ferlay J, Soerjomataram I, Dikshit R, Eser S, Mathers C, Rebelo M, Parkin DM, Forman D, Bray F. (2015) Cancer incidence and mortality worldwide: Sources, methods and major patterns in GLOBOCAN 2012 Int J Cancer; 2015; 136(5): E359-E386
Orlich MJ, Singh PN, Sabaté J, Fan J, Sveen L, Bennett H, Knutsen SF, Beeson WL, Jaceldo-Siegl K, Butler TL, Herring RP, Fraser GE. (2015). Vegetarian Dietary Patterns and the Risk of Colorectal Cancers. AMA Intern Med. 2015 Mar 9.
Sitthiphong P, Lovegrove JA, Rowland I, Klinder A (2015) Flavonoid-rich and flavonoid-poor fruit and vegetables intake prevents DNA damage in human lymphocytes – a randomized controlled trial (in prepapration)
WCRF/AICR (2011). Food, Nutrition, Physical Activity, and the Prevention of Cancer Continuous Update Project Colorectal cancer. http://www.wcrf.org/sites/default/files/Colorectal-Cancer-2011-Report.pdf