Published online Jun 28, 2018. doi: 10.3748/wjg.v24.i24.2617
Peer-review started: March 30, 2018
First decision: April 19, 2018
Revised: May 8, 2018
Accepted: May 18, 2018
Article in press: May 18, 2018
Published online: June 28, 2018
Colorectal cancer (CRC) is a common disease with considerable mortality rates in the western world. The association between diet and CRC and adenomas has been investigated, and risk factors, which have been identified, include high intake of red or processed meat and alcohol, and low intake of fruit, vegetables, whole grains and legumes. The Mediterranean diet (MD) is a plant based dietary pattern, previously associated with a lower incidence of several chronic diseases, including several types of cancer, and specifically CRC and colonic adenomas. It has been suggested that the anti-neoplastic properties of the MD are due to a high fiber and phytochemical content, typically low amounts of calorie-dense foods such as sweets, and red meat.
Given the high prevalence of CRC in the western world there is need for evidence-based means of prevention. Nowadays, the recommended strategies for prevention of CRC include screening for early detection, and reduction of CRC risk through lifestyle and certain dietary regimens, although a specific dietary pattern has not been identified.
The aim of this study was to evaluate the association between the MD dietary pattern, and advanced colorectal polyps (adenoma and serrated adenoma). As these are the main precursor lesions of CRC, elucidating this association may imply a dietary strategy in lowering colorectal neoplasia risk. If the hypothesis of this study is confirmed, larger prospective studies will be able to further elucidate the temporal association and strengthen a causal link between the adherence to the MD diet and CRC prevention.
We collected detailed information of 783 subjects who underwent colonoscopy at the Tel Aviv medical center, including 385 controls, 192 cases on non-advanced adenomas and 206 cases with advanced polyps (advanced adenoma n = 165, advanced serrated adenoma n = 11, multiple non-advanced adenomatous or serrated adenomas n = 30). Within two months after their colonoscopy, patients underwent blood tests, anthropometric measurements, demographic characteristics and medical history, current medications and indication for colonoscopy were documented, lifestyle, and dietary intake were assessed with a structured questionnaire. Mean daily and weekly intake was calculated for each food group: whole grains, vegetables and legumes, nuts and seeds, fruit, fish, poultry, red and processed meat, sugar-sweetened beverages, alcoholic beverages, and the ratio of mono-unsaturated fatty-acids to saturated fatty-acids (MUFA/SFA). For beneficial components (whole grains, vegetables and legumes, nuts and seeds, fruit, fish, poultry, and MUFA/SFA), consumption at or above the group median was considered as adherence, while for components presumed to be detrimental (red and processed meat, sugar-sweetened beverages, and alcoholic beverages), consumption below the group median was considered as adherence. The MD score was calculated as the sum of all adhered components.
Main findings include a significant negative association between the MD score and advanced colorectal polyps, which demonstrated a dose response relationship. Of all MD components, the ones most highly associated with lower odds of advanced polyps were low intake of sugar-sweetened beverages and red meat, as well as high intake of fish. We conclude that adherence to the MD dietary pattern is associated with lower odds of advanced colorectal polyps. As this is an observational case-control study, further prospective studies are needed to confirm this association.
In this study we show that the MD score is negatively associated with colorectal polyps, and specifically advanced polyps. A significant dose response association was detected with categories of the number of adhered MD components. Also, from all the components of the MD, low intake of sugar-sweetened beverages, red meat and high intake of fish were independently associated with lower odds of advanced polyps. The findings of this study imply that adherence to the MD diet may have a role in colorectal neoplasia progression, and should further be studied as a means of colorectal polyp prevention. This study confirms previous reports regarding the MD and colorectal cancer and adenomas, and adds to the knowledge regarding the specific components of the MD independently associated with lower odds of advanced colorectal polyp. The strengths of this study include the large sample-size case control study design, which enabled testing the association between diet and the rare finding of advanced polyps, in a population which is not at high risk of CRC. Furthermore, we had a meticulous nutritional data collection as well as data on important potential confounders, which we adjusted for.
Future prospective research in the field of dietary CRC prevention should focus on elucidating the temporality and the strength of the association between diet and colorectal polyps. Also, it is advised that future studies elucidate this association within the context of serrated polyps, which our study sample was unable to provide.